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L6566B
Multi-mode controller for SMPS
Features

Selectable multi-mode operation: fixed frequency or quasi-resonant On-board 700 V high-voltage start-up Advanced light load management Low quiescent current (< 3 mA) Adaptive UVLO Line feedforward for constant power capability vs mains voltage Pulse-by-pulse OCP, shutdown on overload (latched or autorestart) Transformer saturation detection Programmable frequency modulation for EMI reduction Latched or autorestart OVP Brownout protection -600/+800 mA totem pole gate driver with active pull-down during UVLO SO16N package Block diagram
VREF 10 1 HV SS 14 SOFT-START & FAULT MNGT TIME OUT COMP 9 VFF 15 LOW CLAMP OFF2 & DISABLE OVP
Icharge
SO16N
Applications

Hi-end AC-DC adapter/charger LCD TV/monitor, PDP digital consumer, IT equipment single-stage PFC
Figure 1.
VCC
6.4V + 7.7V Q CS LEB 1.5 V 7 VCC OVPL
IHV
VCC
5
VOLTAGE REGULATOR & ADAPTIVE UVLO
Reference voltages Internal supply UVLO
LINE VOLTAGE FEEDFORWARD
VCC
UVLO_SHF
Vth + -
+ PWM
+ OCP
+
-
6 FMOD + OSC 13
400 uA
Hiccup-mode OCP logic
OCP2
14V 4 GD
5.7V
BURST-MODE
OSCILLATOR MODE SELECTION & TURN-ON LOGIC + OVERVOLTAGE PROTECTION OVP LATCH IC_LATCH
ZERO CURRENT DETECTOR
R Q S DRIVER
MODE/SC
12 50 mV 100 mV
TIME OUT OVPL 4.5V + DIS 8 3 OFF2
ZCD 11
16 AC_OK
3V
15 A 0.450V 0.485V +
AC_FAIL UVLO
DISABLE
May 2008
Rev 2
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Contents
L6566B
Contents
1 2 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1 2.2 Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3
Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1 3.2 Maximum rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4 5
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 5.11 5.12 5.13 5.14 High-voltage start-up generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Zero current detection and triggering block; oscillator block . . . . . . . . . . 21 Burst-mode operation at no load or very light load . . . . . . . . . . . . . . . . . . 24 Adaptive UVLO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 PWM control block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 PWM comparator, PWM latch and voltage feedforward blocks . . . . . . . . 27 Hiccup-mode OCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Frequency modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Latched disable function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Soft-start and delayed latched shutdown upon overcurrent . . . . . . . . . . . 33 OVP block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Brownout protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Slope compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Summary of L6566B power management functions . . . . . . . . . . . . . . . . 41
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L6566B
Contents
6 7 8 9
Application examples and ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
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List of tables
L6566B
List of tables
Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. Table 9. Table 10. Table 11. Pin functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Thermal data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 L6566B light load management features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 L6566B protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 External circuits that determine IC behavior upon OVP and OCP . . . . . . . . . . . . . . . . . . . 45 SO16N mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
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L6566B
List of figures
List of figures
Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. Figure 20. Figure 21. Figure 22. Figure 23. Figure 24. Figure 25. Figure 26. Figure 27. Figure 28. Figure 29. Figure 30. Figure 31. Figure 32. Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Typical system block diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Pin connection (through top view) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Multi-mode operation with QR option active . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 High-voltage start-up generator: internal schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Timing diagram: normal power-up and power-down sequences . . . . . . . . . . . . . . . . . . . . 19 Timing diagram showing short-circuit behavior (SS pin clamped at 5V). . . . . . . . . . . . . . . 20 Zero current detection block, triggering block, oscillator block and related logic . . . . . . . . 20 Drain ringing cycle skipping as the load is gradually reduced . . . . . . . . . . . . . . . . . . . . . . 22 Operation of ZCD, triggering and oscillator blocks (QR option active) . . . . . . . . . . . . . . . . 23 Load-dependent operating modes: timing diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Addition of an offset to the current sense lowers the burst-mode operation threshold . . . . 25 Adaptive UVLO block. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Possible feedback configurations that can be used with the L6566B . . . . . . . . . . . . . . . . . 26 Externally controlled burst-mode operation by driving pin COMP: timing diagram. . . . . . . 27 Typical power capability change vs. input voltage in QR flyback converters . . . . . . . . . . . 28 Left: Overcurrent setpoint vs. VFF voltage; right: Line Feedforward function block . . . . . . 29 Hiccup-mode OCP: timing diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Frequency modulation circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Operation after latched disable activation: timing diagram . . . . . . . . . . . . . . . . . . . . . . . . . 33 Soft-start pin operation under different operating conditions and settings . . . . . . . . . . . . . 34 OVP Function: internal block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 OVP function: timing diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Maximum allowed duty cycle vs. switching frequency for correct OVP detection. . . . . . . . 37 Brownout protection: internal block diagram and timing diagram . . . . . . . . . . . . . . . . . . . . 38 Voltage sensing techniques to implement brownout protection with the L6566B . . . . . . . . 39 Slope compensation waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Typical low-cost application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Typical full-feature application schematic (QR operation) . . . . . . . . . . . . . . . . . . . . . . . . . 44 Typical full-feature application schematic (FF operation) . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Frequency foldback at light load (FF operation) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Latched shutdown upon mains overvoltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
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Description
L6566B
1
Description
The L6566B is an extremely versatile current-mode primary controller ICs, specifically designed for high-performance offline flyback converters. It is also suited for single-stage single-switch input-current-shaping converters (single-stage PFC) for applications supposed to comply with EN61000-3-2 or JEITA-MITI regulations. Both fixed-frequency (FF) and quasi-resonant (QR) operation are supported. The user can pick either of the two depending on application needs. The device features an externally programmable oscillator: it defines converter's switching frequency in FF mode and the maximum allowed switching frequency in QR mode. When FF operation is selected, the ICs work like a standard current-mode controller with a maximum duty cycle limited at 70 % min. The oscillator frequency can be modulated to mitigate EMI emissions. QR operation, when selected, occurs at heavy load and is achieved through a transformer demagnetization sensing input that triggers MOSFET's turn-on. Under some conditions, ZVS (zero-voltage switching) can be achieved. Converter's power capability rise with the mains voltage is compensated by line voltage feedforward. At medium and light load, as the QR operating frequency equals the oscillator frequency, a function (valley skipping) is activated to prevent further frequency rise and keep the operation as close to ZVS as possible. With either FF or QR operation, at very light load the ICs enter a controlled burst-mode operation that, along with the built-in non-dissipative high-voltage start-up circuit and the low quiescent current, helps keep low the consumption from the mains and meet energy saving recommendations. An innovative adaptive UVLO helps minimize the issues related to the fluctuations of the self-supply voltage due to transformer's parasites. The protection functions included in this device are: not-latched input undervoltage (brownout), output OVP (auto-restart or latch-mode selectable), a first-level OCP with delayed shutdown to protect the system during overload or short circuit conditions (autorestart or latch-mode selectable) and a second-level OCP that is invoked when the transformer saturates or the secondary diode fails short. A latched disable input allows easy implementation of OTP with an external NTC, while an internal thermal shutdown prevents IC overheating. Programmable soft-start, leading-edge blanking on the current sense input for greater noise immunity, slope compensation (in FF mode only), and a shutdown function for externally controlled burst-mode operation or remote ON/OFF control complete the equipment of this device.
6/51
L6566B Figure 2. Typical system block diagram
Description
FLYBACK DC-DC CONVERTER
Rectified & Filtered Mains Voltage
Voutdc
L6566B
7/51
Pin settings
L6566B
2
2.1
Pin settings
Connections
Figure 3. Pin connection (through top view)
HVS N.C. GND GD Vcc FMOD CS DIS
1 2 3 4 5 6 7 8
16 15 14 13 12 11 10 9
AC_OK VFF SS OSC MODE/SC ZCD VREF COMP
2.2
Pin description
Table 1.
N Pin
Pin functions
Function High-voltage start-up. The pin, able to withstand 700 V, is to be tied directly to the rectified mains voltage. A 1 mA internal current source charges the capacitor connected between Vcc pin (5) and GND pin (3) until the voltage on the Vcc pin reaches the turn-on threshold, then it is shut down. Normally, the generator is reenabled when the Vcc voltage falls below 5 V to ensure a low power throughput during short circuit. Otherwise, when a latched protection is tripped the generator is re-enabled 0.5 V below the turn-on threshold, to keep the latch supplied; or, when the IC is turned off by pin COMP (9) pulled low the generator is active just below the UVLO threshold to allow a faster restart. Not internally connected. Provision for clearance on the PCB to meet safety requirements. Ground. Current return for both the signal part of the IC and the gate drive. All of the ground connections of the bias components should be tied to a track going to this pin and kept separate from any pulsed current return. Gate driver output. The totem pole output stage is able to drive power MOSFET's and IGBT's with a peak current capability of 800 mA source/sink.
1
HVS
2
N.C.
3
GND
4
GD
8/51
L6566B Table 1.
N Pin
Pin settings Pin functions (continued)
Function Supply voltage of both the signal part of the IC and the gate driver. The internal high voltage generator charges an electrolytic capacitor connected between this pin and GND (pin 3) as long as the voltage on the pin is below the turn-on threshold of the IC, after that it is disabled and the chip is turned on. The IC is disabled as the voltage on the pin falls below the UVLO threshold. This threshold is reduced at light load to counteract the natural reduction of the self-supply voltage. Sometimes a small bypass capacitor (0.1 F typ.) to GND might be useful to get a clean bias voltage for the signal part of the IC. Frequency modulation input. When FF mode operation is selected, a capacitor connected from this pin to GND (pin 3) is alternately charged and discharged by internal current sources. As a result, the voltage on the pin is a symmetrical triangular waveform with the frequency related to the capacitance value. By connecting a resistor from this pin to pin 13 (OSC) it is possible to modulate the current sourced by the OSC pin and then the oscillator frequency. This modulation is to reduce the peak value of EMI emissions by means of a spread-spectrum action. If the function is not used, the pin will be left open. Input to the PWM comparator. The current flowing in the MOSFET is sensed through a resistor, the resulting voltage is applied to this pin and compared with an internal reference to determine MOSFET's turn-off. The pin is equipped with 150 ns min. blanking time after the gate-drive output goes high for improved noise immunity. A second comparison level located at 1.5 V latches the device off and reduces its consumption in case of transformer saturation or secondary diode short circuit. The information is latched until the voltage on the Vcc pin (5) goes below the UVLO threshold, hence resulting in intermittent operation. A logic circuit improves sensitivity to temporary disturbances. IC's latched disable input. Internally the pin connects a comparator that, when the voltage on the pin exceeds 4.5 V, latches off the IC and brings its consumption to a lower value. The latch is cleared as the voltage on the Vcc pin (5) goes below the UVLO threshold, but the HV generator keeps the Vcc voltage high (see pin 1 description). It is then necessary to recycle the input power to restart the IC. For a quick restart pull pin 16 (AC_OK) below the disable threshold (see pin 16 description). Bypass the pin with a capacitor to GND (pin 3) to reduce noise pickup. Ground the pin if the function is not used. Control input for loop regulation. The pin will be driven by the phototransistor (emitter-grounded) of an optocoupler to modulate its voltage by modulating the current sunk. A capacitor placed between the pin and GND (3), as close to the IC as possible to reduce noise pick-up, sets a pole in the output-to-control transfer function. The dynamics of the pin is in the 2.5 to 5 V range. A voltage below an internally defined threshold activates burst-mode operation. The voltage at the pin is bottom-clamped at about 2 V. If the clamp is externally overridden and the voltage is pulled below 1.4 V the IC will shut down. An internal generator furnishes an accurate voltage reference (5 V 2 %) that can be used to supply few mA to an external circuit. A small film capacitor (0.1 F typ.), connected between this pin and GND (3), is recommended to ensure the stability of the generator and to prevent noise from affecting the reference. This reference is internally monitored by a separate auxiliary reference and any failure or drift will cause the IC to latch off.
5
Vcc
6
FMOD
7
CS
8
DIS
9
COMP
10
VREF
9/51
Pin settings Table 1.
N Pin
L6566B Pin functions (continued)
Function Transformer demagnetization sensing input for quasi-resonant operation and OVP input. The pin is externally connected to the transformer's auxiliary winding through a resistor divider. A negative-going edge triggers MOSFET's turn-on if QR mode is selected. A voltage exceeding 5 V shuts the IC down and brings its consumption to a lower value (OVP). Latch-off or auto-restart mode is selectable externally. This function is strobed and digitally filtered to increase noise immunity.
11
ZCD
Operating mode selection. If the pin is connected to the VREF pin (7) quasi-resonant operation is selected, the oscillator (pin 13, OSC) determines the maximum allowed operating frequency. Fixed-frequency operation is selected if the pin is not tied to VREF, in which case 12 MODE/SC the oscillator determines the actual operating frequency, the maximum allowed duty cycle is set at 70 % min. and the pin delivers a voltage ramp synchronized to the oscillator when the gate-drive output is high; the voltage delivered is zero while the gate-drive output is low. The pin is to be connected to pin CS (7) via a resistor for slope compensation. Oscillator pin. The pin is an accurate 1 V voltage source, and a resistor connected from the pin to GND (pin 3) defines a current. This current is internally used to set the oscillator frequency that defines the maximum allowed switching frequency of the L6566B, if working in QR mode, or the operating switching frequency if working in FF mode. Soft-start current source. At start-up a capacitor Css between this pin and GND (pin 3) is charged with an internal current generator. During the ramp, the internal reference clamp on the current sense pin (7, CS) rises linearly starting from zero to its final value, thus causing the duty cycle to increase progressively starting from zero as well. During soft-start the adaptive UVLO function and all functions monitoring pin COMP are disabled. The soft-start capacitor is discharged whenever the supply voltage of the IC falls below the UVLO threshold. The same capacitor is used to delay IC's shutdown (latch-off or auto-restart mode selectable) after detecting an overload condition (OLP). Line voltage feedforward input. The information on the converter's input voltage is fed into the pin through a resistor divider and is used to change the setpoint of the pulse-by-pulse current limitation (the higher the voltage, the lower the setpoint). The linear dynamics of the pin ranges from 0 to 3 V. A voltage higher than 3 V makes the IC stop switching. If feedforward is not desired, tie the pin to GND (pin 3) directly if a latch-mode OVP is not required (see pin 11, ZCD) or through a 10 k min. resistor if a latch-mode OVP is required. Bypass the pin with a capacitor to GND (pin 3) to reduce noise pick-up. Brownout protection input. A voltage below 0.45 V shuts down (not latched) the IC, lowers its consumption and clears the latch set by latched protections (DIS > 4.5 V, SS > 6.4 V, VFF > 6.4 V). IC's operation is re-enabled as the voltage exceeds 0.45 V. The comparator is provided with current hysteresis: an internal 15 A current generator is ON as long as the voltage on the pin is below 0.45 V and is OFF if this value is exceeded. Bypass the pin with a capacitor to GND (pin 3) to reduce noise pick-up. Tie to Vcc with a 220 to 680 k resistor if the function is not used.
13
OSC
14
SS
15
VFF
16
AC_OK
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L6566B
Electrical data
3
3.1
Electrical data
Maximum rating
Table 2.
Symbol VHVS IHVS VCC VFMOD Vmax Vmax IZCD VMODE/SC VOSC PTOT TSTG TJ
Absolute maximum ratings
Pin 1 1 5 6 7, 8, 10, 14 9, 15, 16 11 12 13 Parameter Voltage range (referred to ground) Output current IC supply voltage (Icc = 20 mA) Voltage range Analog inputs and outputs Maximum pin voltage (Ipin 1 mA) Zero current detector max. current Voltage range Voltage range Power dissipation @TA = 50 C Storage temperature Junction operating temperature range Value -0.3 to 700 Self-limited Self-limited -0.3 to 2 -0.3 to 7 Self-limited 5 -0.3 to 5.3 -0.3 to 3.3 0.75 -55 to 150 -40 to 150 mA V V W C C V V Unit V
3.2
Thermal data
Table 3.
Symbol RthJA
Thermal data
Parameter Thermal resistance junction to ambient Value 120 Unit C/W
11/51
Electrical characteristics
L6566B
4
Electrical characteristics
(TJ = -25 to 125C, VCC = 12, CO = 1 nF; MODE/SC = VREF, RT = 20 k from OSC to GND, unless otherwise specified).
Table 4.
Symbol
Electrical characteristics
Parameter Test condition Min Typ Max Unit
Supply voltage Vcc VccOn VccOff Hys VZ Operating range after turn-on Turn-on threshold Turn-off threshold Hysteresis Zener voltage VCOMP > VCOMPL VCOMP = VCOMPO
(1) (1) (1)
10.6 8 13 14 10 7.6 4 23 25
23 V 23 15 10.6 V 8.0 V 27 V V
VCOMP > VCOMPL VCOMP = VCOMPO
9.4 7.2
VCOMP > VCOMPL Icc = 20 mA, IC disabled
Supply current Istart-up Iq Icc Iqdis Start-up current Quiescent current Operating supply current Quiescent current IC latched off 440 500 Before turn-on, Vcc = 13 V After turn-on, VZCD = VCS = 1 V MODE/SC open IC disabled
(2)
200 2.6 4 330
250 2.8 4.6 2500
A mA mA A
High-voltage start-up generator VHV VHVstart Icharge IHV, ON IHV, OFF Breakdown voltage Start voltage Vcc charge current ON-state current OFF-state leakage current IHV < 100 A IVcc < 100 A VHV > VHvstart, Vcc > 3 V VHV > VHvstart, Vcc > 3 V VHV > VHvstart, Vcc = 0 VHV = 400 V Vcc falling
(1)
700 65 0.55 80 0.85 100 1 1.6
V V mA mA 0.8 40 A
4.4 12.5 9.4
5 13.5 10
5.6 14.5 10.6 V
VCCrestart
Vcc restart voltage
IC latched off
Disabled by VCOMP < VCOMPOFF
(1)
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L6566B Table 4.
Symbol Reference voltage VREF VREF IREF Output voltage Total variation Short circuit current Sink capability in UVLO VOV Overvoltage threshold
(1)
Electrical characteristics Electrical characteristics (continued)
Parameter Test condition Min Typ Max Unit
TJ = 25 C; IREF = 1 mA
4.95 4.9 10
5
5.05 5.1 30
V V mA V V
IREF = 1 to 5 mA, Vcc = 10.6 to 23 V VREF = 0 Vcc = 6 V; Isink = 0.5 mA
0.2 5.3 5.7
0.5
Internal oscillator Operating range fsw Oscillation frequency TJ = 25 C, VZCD = 0, MODE/SC = open Vcc =12 to 23 V, VZCD = 0, MODE/SC = open VOSC Dmax Voltage reference Maximum duty cycle
(3)
10 95 93 0.97 70 100 100 1
300 105 107 1.03 75 V % kHz
MODE/SC = open, VCOMP = 5 V
Brownout protection Voltage falling (turn-off) Vth IHys Threshold voltage Voltage rising (turn-on) Current hysteresis Vcc > 5 V, VVFF = 0.3 V
(1)
0.432 0.452 12 3
0.450 0.485 15 3.15
0.468 0.518 18 3.3
V V A V
VAC_OK_CL Clamp level Line voltage feedforward IVFF VVFF VOFF VVFFlatch Kc KFF Input bias current Linear operation range IC disable voltage Latch-off/clamp level Control voltage gain Feedforward gain
(3) (3)
IAC_OK = 100 A
VVFF = 0 to 3 V, VZCD < VZCDth VZCD > VZCDth -0.7 -1 0 to 3 3 VZCD > VZCDth VVFF = 1 V, VCOMP = 4 V VVFF = 1 V, VCOMP = 4 V 3.15 6.4 0.4 0.04
-1
A mA V
3.3
V V V/V V/V
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Electrical characteristics Table 4.
Symbol
L6566B
Electrical characteristics (continued)
Parameter Test condition Min Typ Max Unit
Current sense comparator ICS tLEB td(H-L) Input bias current Leading edge blanking Delay to output VCOMP = VCOMPHI, VVFF = 0 V VCSx Overcurrent setpoint VCOMP = VCOMPHI, VVFF = 1.5 V VCOMP = VCOMPHI, VVFF = 3.0 V VCSdis Hiccup-mode OCP level
(1)
VCS = 0 150 250
-1 300 100 0.92 0.45 1 0.5 0 1.4 1.5 1.08 0.55 0.1 1.6
A ns ns
V
V
PWM control VCOMPHI VCOMPLO VCOMPSH ICOMP RCOMP VCOMPBM Hys ICLAMPL VCOMPOFF VCOMPO Upper clamp voltage Lower clamp voltage Linear dynamics upper limit Max. source current Dynamic resistance Burst-mode threshold Burst-mode hysteresis Lower clamp capability Disable threshold Level for lower UVLO off threshold (voltage falling) Level for higher UVLO off threshold (voltage rising) VCOMP = 2 V Voltage falling
(3) (3) MODE/SC (3) (3)
ICOMP = 0 ISOURCE = -1 mA
(1)
5.7 2.0 4.8 320 5 400 25 2.52 = open 2.7 2.65 2.85 20 -3.5 1.4 2.61 = open 3.02 2.9 2.75 3.15 3.05 3.55 2.89 -1.5 2.78 5.2 480
V V V A k V 3 mV mA V V 3.28 3.2 V 3.69
VVFF = 0 V
VCOMP = 3.3 V VCOMP = 2.6 to 4.8 V
(1) (1) MODE/SC
VCOMPL
MODE/SC = open
3.41
14/51
L6566B Table 4.
Symbol
Electrical characteristics Electrical characteristics (continued)
Parameter Test condition Min Typ Max Unit
Zero current detector/ overvoltage protection VZCDH VZCDL VZCDA VZCDT IZCD IZCDsrc IZCDsnk TBLANK1 VZCDth TBLANK2 Upper clamp voltage Lower clamp voltage Arming voltage Triggering voltage Internal pull-up Source current capability Sink current capability Turn-on inhibit time OVP threshold OVP strobe delay After gate-drive going low IZCD = 3 mA IZCD = - 3 mA
(1) (1)
5.4
5.7 -0.4
6
V V
positive-going edge negative-going edge
85 30
100 50
115 70 -1
mV mV A
VCOMP < VCOMPSH VZCD < 2 V, VCOMP = VCOMPHI VZCD = VZCDL VZCD = VZCDH After gate-drive going low 4.85 -130 -3 3 2.5 5 2 -100
-70 mA mA s 5.15 V s
Latched shutdown function IOTP VOTP Input bias current Disable threshold VDIS = 0 to VOTP
(1)
-1 4.32 4.5 4.68
A V
Thermal shutdown Vth Hys Shutdown threshold Hysteresis 160 50 C C
External oscillator (frequency modulation) fFMOD --Vpk Vvy IFMOD Oscillation frequency Usable frequency range Peak voltage Valley voltage Charge/discharge current
(3)
CMOD = 0.1 F
600 0.05
750
900 15
Hz kHz V V A
1.5 0.5 150
Mode selection / slope compensation MODEth SCpk SCvy Threshold for QR operation Ramp peak (MODE/SC = open) Ramp starting value (MODE/SC = open) Ramp voltage (MODE/SC = open) Source capability (MODE/SC = open) RS-COMP = 3 k to GND, GD pin high, VCOMP = 5 V RS-COMP = 3 k to GND, GD pin high GD pin low VS-COMP = VS-COMPpk 0.8 3 1.7 0.3 0 V V V V mA
15/51
Electrical characteristics Table 4.
Symbol Soft-start ISS1 Charge current ISS2 ISSdis VSSclamp VSSDIS VSSLAT Gate driver VGDH VGDL Isourcepk Isinkpk tf tr VGDclamp Output high voltage Output low voltage Output source peak current Output sink peak current Fall time Rise time Output clamp voltage UVLO saturation
1. Parameters tracking one another. 2. See Table 6 on page 41 and Table 7 on page 42 3. The voltage feedforward block output is given by:
L6566B
Electrical characteristics (continued)
Parameter Test condition Min. Typ. Max. Unit
TJ = 25 C, VSS < 2 V, VCOMP = 4 V TJ = 25 C, VSS > 2 V, VCOMP =VCOMPHi
14 3.5 3.5
20 5 5 2
26 A 6.5 6.5 A V 5.15 V V
Discharge current High saturation voltage Disable level Latch-off level
VSS > 2 V VCOMP = 4 V
(1)
VCOMP = VCOMPHi
4.85
5 6.4
VCOMP = VCOMPHi
IGDsource = 5 mA, Vcc = 12 V IGDsink = 100 mA
9.8
11 0.75
V V A A
-0.6 0.8 40 50 IGDsource = 5 mA; Vcc = 20 V Vcc = 0 to Vccon, Isink = 1 mA 10 11.3 0.9 15 1.1
ns ns V V
Vcs = Kc (VCOMP - 2.5 ) - K FF VVFF
16/51
L6566B
Application information
5
Application information
The L6566B is a versatile peak-current-mode PWM controller specific for offline flyback converters. The device allows either fixed-frequency (FF) or quasi-resonant (QR) operation, selectable with the pin MODE/SC (12): forcing the voltage on the pin over 3 V (e.g. by tying it to the 5 V reference externally available at pin VREF, 10) will activate QR operation, otherwise the device will be FF-operated. Irrespective of the operating option selected by pin 12, the device is able to work in different modes, depending on the converter's load conditions. If QR operation is selected (see Figure 4): 1. QR mode at heavy load. Quasi-resonant operation lies in synchronizing MOSFET's turn-on to the transformer's demagnetization by detecting the resulting negative-going edge of the voltage across any winding of the transformer. Then the system works close to the boundary between discontinuous (DCM) and continuous conduction (CCM) of the transformer. As a result, the switching frequency will be different for different line/load conditions (see the hyperbolic-like portion of the curves in Figure 4). Minimum turn-on losses, low EMI emission and safe behavior in short circuit are the main benefits of this kind of operation. 2. Valley-skipping mode at medium/ light load. The externally programmable oscillator of the L6566B, synchronized to MOSFET's turn-on, enables the designer to define the maximum operating frequency of the converter. As the load is reduced MOSFET's turnon will not any more occur on the first valley but on the second one, the third one and so on. In this way the switching frequency will no longer increase (piecewise linear portion in Figure 4). 3. Burst-mode with no or very light load. When the load is extremely light or disconnected, the converter will enter a controlled on/off operation with constant peak current. Decreasing the load will then result in frequency reduction, which can go down even to few hundred hertz, thus minimizing all frequency-related losses and making it easier to comply with energy saving regulations or recommendations. Being the peak current very low, no issue of audible noise arises.
Figure 4. Multi-mode operation with QR option active
fosc
Input voltage
Valley-skipping mode
f sw
Burst-mode Quasi-resonant mode
0 0
P in
Pinmax
17/51
Application information
L6566B
If FF operation is selected: 1. FF mode from heavy to light load. The system operates exactly like a standard current mode control, at a frequency fsw determined by the externally programmable oscillator: both DCM and CCM transformer operation are possible, depending on whether the power that it processes is greater or less than:
Equation 1
Vin VR Vin + V R Pin T = 2 fsw Lp
2
2.
where Vin is the input voltage to the converter, VR the reflected voltage (i.e. the regulated output voltage times the primary-to-secondary turn ratio) and Lp the inductance of the primary winding. PinT is the power level that marks the transition from continuous to discontinuous operation mode of the transformer. Burst-mode with no or very light load. This kind of operation is activated in the same way and results in the same behavior as previously described for QR operation.
The L6566B is specifically designed for applications with no PFC front-end; pin 6 (FMOD) features an auxiliary oscillator that can modulate the switching frequency (when FF operation is selected) in order to mitigate EMI emissions by a spread-spectrum action.
5.1
High-voltage start-up generator
Figure 5 shows the internal schematic of the high-voltage start-up generator (HV generator). It is made up of a high-voltage N-channel FET, whose gate is biased by a 15 M resistor, with a temperature-compensated current generator connected to its source. Figure 5. High-voltage start-up generator: internal schematic
HV
L6566B
15 M
1
Vcc_OK HV_EN I HV
5 CONTROL I charge 3 GND
Vcc
18/51
L6566B
Application information
With reference to the timing diagram of Figure 6, when power is first applied to the converter the voltage on the bulk capacitor (Vin) builds up and, at about 80 V, the HV generator is enabled to operate (HV_EN is pulled high) so that it draws about 1 mA. This current, minus the device's consumption, charges the bypass capacitor connected from pin Vcc (5) to ground and makes its voltage rise almost linearly.
Figure 6.
Vin
VHVstart
Timing diagram: normal power-up and power-down sequences
Vcc (pin 5)
VccON VccOFF Vccrestart
regulation is lost here
t
t GD (pin 4) t
HV_EN
Vcc_OK
t
Icharge
0.85 mA
t
Power-on
Normal operation
Power-off
t
As the Vcc voltage reaches the turn-on threshold (14 V typ.) the device starts operating and the HV generator is cut off by the Vcc_OK signal asserted high. The device is powered by the energy stored in the Vcc capacitor until the self-supply circuit (typically an auxiliary winding of the transformer and a steering diode) develops a voltage high enough to sustain the operation. The residual consumption of this circuit is just the one on the 15 M resistor (10 mW at 400 Vdc), typically 50-70 times lower, under the same conditions, as compared to a standard start-up circuit made with external dropping resistors. At converter power-down the system will lose regulation as soon as the input voltage is so low that either peak current or maximum duty cycle limitation is tripped. Vcc will then drop and stop IC activity as it falls below the UVLO threshold (10 V typ.). The Vcc_OK signal is de-asserted as the Vcc voltage goes below a threshold VCCrest located at about 5V. The HV generator can now restart. However, if Vin < Vinstart, as illustrated in Figure 6, HV_EN is deasserted too and the HV generator is disabled. This prevents converter's restart attempts and ensures monotonic output voltage decay at power-down in systems where brownout protection (see the relevant section) is not used. The low restart threshold VCCrest ensures that, during short circuits, the restart attempts of the device will have a very low repetition rate, as shown in the timing diagram of Figure 7 on page 20, and that the converter will work safely with extremely low power throughput.
19/51
Application information Figure 7.
L6566B Timing diagram showing short-circuit behavior (SS pin clamped at 5 V)
Short circuit occurs here
Vcc (pin 5)
VccON VccOFF Vccrestart
GD (pin 4) Vcc_OK
Trep < 0.03Trep
t
t
Icharge
0.85 mA
t
t
Figure 8.
Zero current detection block, triggering block, oscillator block and related logic
COMP 9 VFF 15 line FFWD +Vin
L6566B
ZCD RZ1 RZ2 11 5.7V BLANKING TIME
blanking START
PWM
7
CS
R 100 mV 50 mV
4 Q
DRIVER
GD
+
Strobe
MONO STABLE
TURN-ON LOGIC
Q
S
OSCILLATOR
Reset
Rs
+ 5V
S/H
4:1 Counter
FAULT
AUXILIARY OSCILLATOR 6 FMOD
RMOD CMOD RT
13 OSC
20/51
L6566B
Application information
5.2
Zero current detection and triggering block; oscillator block
The zero current detection (ZCD) and triggering blocks switch on the external MOSFET if a negative-going edge falling below 50 mV is applied to the input (pin 11, ZCD). To do so the triggering block must be previously armed by a positive-going edge exceeding 100 mV. This feature is typically used to detect transformer demagnetization for QR operation, where the signal for the ZCD input is obtained from the transformer's auxiliary winding used also to supply the L6566B. The triggering block is blanked for TBLANK = 2.5 s after MOSFET's turn-off to prevent any negative-going edge that follows leakage inductance demagnetization from triggering the ZCD circuit erroneously. The voltage at the pin is both top and bottom limited by a double clamp, as illustrated in the internal diagram of the ZCD block of Figure 8 on page 20. The upper clamp is typically located at 5.7 V, while the lower clamp is located at -0.4 V. The interface between the pin and the auxiliary winding will be a resistor divider. Its resistance ratio will be properly chosen (see Section 5.11: OVP block on page 35) and the individual resistance values (RZ1, RZ2) will be such that the current sourced and sunk by the pin be within the rated capability of the internal clamps ( 3 mA). At converter power-up, when no signal is coming from the ZCD pin, the oscillator starts up the system. The oscillator is programmed externally by means of a resistor (RT) connected from pin OSC (13) to ground. With good approximation the oscillation frequency fosc will be:
Equation 2
fosc
2 10 3 RT
(with fosc in kHz and RT in k). As the device is turned on, the oscillator starts immediately; at the end of the first oscillator cycle, being zero the voltage on the ZCD pin, the MOSFET will be turned on, thus starting the first switching cycle right at the beginning of the second oscillator cycle. At any switching cycle, the MOSFET is turned off as the voltage on the current sense pin (CS, 7) hits an internal reference set by the line feedforward block, and the transformer starts demagnetization. If this completes (hence a negative-going edge appears on the ZCD pin) after a time exceeding one oscillation period Tosc = 1/fosc from the previous turn-on, the MOSFET will be turned on again - with some delay to ensure minimum voltage at turn-on - and the oscillator ramp will be reset. If, instead, the negative-going edge appears before Tosc has elapsed, it will be ignored and only the first negative-going edge after Tosc will turn-on the MOSFET and synchronize the oscillator. In this way one or more drain ringing cycles will be skipped ("valley-skipping mode", Figure 9) and the switching frequency will be prevented from exceeding fosc.
21/51
Application information
L6566B
Figure 9.
VDS
Drain ringing cycle skipping as the load is gradually reduced
VDS VDS
t TON TFW Tosc TV Tosc
t
t
Tosc
Pin = Pin'
(limit condition)
Pin = Pin'' < Pin'
Pin = Pin''' < Pin''
Note:
When the system operates in valley skipping-mode, uneven switching cycles may be observed under some line/load conditions, due to the fact that the OFF-time of the MOSFET is allowed to change with discrete steps of one ringing cycle, while the OFF-time needed for cycle-by-cycle energy balance may fall in between. Thus one or more longer switching cycles will be compensated by one or more shorter cycles and vice versa. However, this mechanism is absolutely normal and there is no appreciable effect on the performance of the converter or on its output voltage.
If the MOSFET is enabled to turn on but the amplitude of the signal on the ZCD pin is smaller than the arming threshold for some reason (e.g. a heavy damping of drain oscillations, like in some single-stage PFC topologies, or when a turn-off snubber is used), MOSFET's turn-on cannot be triggered. This case is identical to what happens at start-up: at the end of the next oscillator cycle the MOSFET will be turned on, and a new switching cycle will take place after skipping no more than one oscillator cycle. The operation described so far does not consider the blanking time TBLANK after MOSFET's turn off, and actually TBLANK does not come into play as long as the following condition is met:
Equation 3
D 1-
TBLANK Tosc
where D is the MOSFET duty cycle. If this condition is not met, things do not change substantially: the time during which MOSFET's turn-on is inhibited is extended beyond Tosc by a fraction of TBLANK. As a consequence, the maximum switching frequency will be a little lower than the programmed value fosc and valley-skipping mode may take place slightly earlier than expected. However this is quite unusual: setting fosc = 150 kHz, the phenomenon can be observed at duty cycles higher than 60 %. See Section 5.11: OVP block on page 35 for further implications of TBLANK. If the voltage on the COMP pin (9) saturates high, which reveals an open control loop, an internal pull-up keeps the ZCD pin close to 2 V during MOSFET's OFF-time to prevent noise from false triggering the detection block. When this pull-up is active, the ZCD pin might not be able to go below the triggering threshold, which would stop the converter. To allow autorestart operation, however ensuring minimum operating frequency in these conditions, the oscillator frequency that retriggers MOSFET's turn-on is that of the external oscillator divided by 128. Additionally, to prevent malfunction at converter's start-up, the pull-up is disabled during the initial soft-start (see the relevant section). However, to ensure a correct
22/51
L6566B
Application information
start-up, at the end of the soft-start phase the output voltage of the converter must meet the condition:
Equation 4
Vout >
Ns R Z1 I ZCD Naux
where Ns is the turn number of the secondary winding, Naux the turn number of the auxiliary winding and IZCD the maximum pull-up current (130 A). The operation described so far under different operating conditions for the converter is illustrated in the timing diagrams of Figure 10. If the FF option is selected the operation will be exactly equal to that of a standard currentmode PWM controller. It will work at a frequency fsw = fosc; both DCM and CCM transformer's operation are possible, depending on the operating conditions (input voltage and output load) and on the design of the power stage. The MOSFET is turned on at the beginning of each oscillator cycle and is turned off as the voltage on the current sense pin reaches an internal reference set by the line feedforward block. The maximum duty cycle is limited at 70 % minimum. The signal on the ZCD pin in this case is used only for detecting feedback loop failures (see Section 5.11: OVP block on page 35 ).
Figure 10. Operation of ZCD, triggering and oscillator blocks (QR option active)
ZCD (pin 11)
100 mV 50 mV
ZCD (pin 11)
100 mV 50 mV
ZCD (pin 11)
100 mV 50 mV
Oscillator ramp
Oscillator ramp
Oscillator ramp
ZCD blanking time
armed trigger
ZCD blanking time
ZCD blanking time
Arm/Trigger
Arm/Trigger
Arm/Trigger
ON-enable
ON-enable
ON-enable
PWM latch Set
PWM latch Set
PWM latch Set
PWM latch Reset
PWM latch Reset
PWM latch Reset
GD (pin 4)
GD (pin 4)
GD (pin 4)
a) full load
b) light load
c) start-up
23/51
Application information
L6566B
5.3
Burst-mode operation at no load or very light load
When the voltage at the COMP pin (9) falls 20 mV below a threshold fixed internally at a value, VCOMPBM, depending on the selected operating mode, the L6566B is disabled with the MOSFET kept in OFF state and its consumption reduced at a lower value to minimize Vcc capacitor discharge. The control voltage now will increase as a result of the feedback reaction to the energy delivery stop (the output voltage will be slowly decaying), the threshold will be exceeded and the device will restart switching again. In this way the converter will work in burst-mode with a nearly constant peak current defined by the internal disable level. A load decrease will then cause a frequency reduction, which can go down even to few hundred hertz, thus minimizing all frequency-related losses and making it easier to comply with energy saving regulations. This kind of operation, shown in the timing diagrams of Figure 11 along with the others previously described, is noise-free since the peak current is low. If it is necessary to decrease the intervention threshold of the burst-mode operation, this can be done by adding a small DC offset on the current sense pin as shown in Figure 12 on page 25.
Note:
The offset reduces the available dynamics of the current signal; thereby, the value of the sense resistor must be determined taking this offset into account. Figure 11. Load-dependent operating modes: timing diagrams
COMP (pin 9)
20 mV hyster.
VCOMPBM
fosc
t
MODE/SC=Open MODE/SC=VREF
fsw
t GD (pin 4)
MODE/SC=Open MODE/SC=VREF
FF Mode QR Mode Burst-mode Burst-mode Valley-skipping Mode FF Mode QR Mode
t
24/51
L6566B
Application information Figure 12. Addition of an offset to the current sense lowers the burst-mode operation threshold
Vcso = Vref Vref 10 4 R R + Rc
L6566B
3 7
Rc R
Rs
5.4
Adaptive UVLO
A major problem when optimizing a converter for minimum no-load consumption is that the voltage generated by the auxiliary winding under these conditions falls considerably as compared even to a few mA load. This very often causes the supply voltage Vcc of the control IC to drop and go below the UVLO threshold so that the operation becomes intermittent, which is undesired. Furthermore, this must be traded off against the need of generating a voltage not exceeding the maximum allowed by the control IC at full load. To help the designer overcome this problem, the device, besides reducing its own consumption during burst-mode operation, also features a proprietary adaptive UVLO function. It consists of shifting the UVLO threshold downwards at light load, namely when the voltage at pin COMP falls below a threshold VCOMPO internally fixed, so as to have more headroom. To prevent any malfunction during transients from minimum to maximum load the normal (higher) UVLO threshold is re-established when the voltage at pin COMP exceeds VCOMPL and Vcc has exceeded the normal UVLO threshold (see Figure 13). The normal UVLO threshold ensures that at full load the MOSFET will be driven with a proper gate-to-source voltage.
Figure 13.
Adaptive UVLO block
VCOMP (pin 9)
Vcc 5 +
VCOMPL VCOMPO
COMP
9 -
R S Q
VccOFF1
VccOFF2 (*)
(*) VccOFF2 < VccOFF1 is selected when Q is high
-
VCOMPL VCOMPO
SW
+
-
Vcc (pin 5)
UVLO
VccOFF1 VccOFF2
t
+
L6566B
Q
t
t
25/51
Application information
L6566B
5.5
PWM control block
The device is specific for secondary feedback. Typically, there is a TL431 on the secondary side and an optocoupler that transfers output voltage information to the PWM control on the primary side, crossing the isolation barrier. The PWM control input (pin 9, COMP) is driven directly by the phototransistor's collector (the emitter is grounded to GND) to modulate the duty cycle (Figure 14, left-hand side circuit). In applications where a tight output regulation is not required, it is possible to use a primarysensing feedback technique. In this approach the voltage generated by the self-supply winding is sensed and regulated. This solution, shown in Figure 14, right-hand side circuit, is cheaper because no optocoupler or secondary reference is needed, but output voltage regulation, especially as a result of load changes, is quite poor.
Figure 14. Possible feedback configurations that can be used with the L6566B
Vout
5
Vcc
L6566B
9 COMP
L6566B
9 COMP
Cs
Naux
TL431
Secondary feedback
Primary feedback
Ideally, the voltage generated by the self-supply winding and the output voltage should be related by the Naux/Ns turn ratio only. Actually, numerous non-idealities, mainly transformer's parasites, cause the actual ratio to deviate from the ideal one. Line regulation is quite good, in the range of 2 %, whereas load regulation is about 5 % and output voltage tolerance is in the range of 10 %. The dynamics of the pin is in the 2.5 to 5 V range. The voltage at the pin is clamped downwards at about 2 V. If the clamp is externally overridden and the voltage on the pin is pulled below 1.4 V the L6566B will shut down. This condition is latched as long as the device is supplied. While the device is disabled, however, no energy is coming from the selfsupply circuit, thus the voltage on the Vcc capacitor will decay and cross the UVLO threshold after some time, which clears the latch and lets the HV generator restart. This function is intended for an externally controlled burst-mode operation at light load with a reduced output voltage, a technique typically used in multi-output SMPS, such as those for TVs or monitors (see the timing diagram Figure 15 on page 27).
26/51
L6566B
Application information Figure 15. Externally controlled burst-mode operation by driving pin COMP: timing diagram
Vcc (pin 5) VccON
VccOFF Vccrestart
Standby is commanded here
COMP (pin 9)
t
GD (pin 4)
t
Vcc_OK
t
Icharge
0.85 mA
t
Vout
t
t
5.6
PWM comparator, PWM latch and voltage feedforward blocks
The PWM comparator senses the voltage across the current sense resistor Rs and, by comparing it to the programming signal delivered by the feedforward block, determines the exact time when the external MOSFET is to be switched off. Its output resets the PWM latch, previously set by the oscillator or the ZCD triggering block, which will assert the gate driver output low. The use of PWM latch avoids spurious switching of the MOSFET that might result from the noise generated ("double-pulse suppression"). Cycle-by-cycle current limitation is realized with a second comparator (OCP comparator) that senses the voltage across the current sense resistor Rs as well and compares this voltage to a reference value Vcsx. Its output is or-ed with that of the PWM comparator (see the circuit schematic in Figure 17 on page 29). In this way, if the programming signal delivered by the feedforward block and sent to the PWM comparator exceeds Vcsx, it will be the OCP comparator to reset first the PWM latch instead of the PWM comparator. The value of Vcsx, thereby, determines the overcurrent setpoint along with the sense resistor Rs. The power that QR flyback converters with a fixed overcurrent setpoint (like fixed-frequency systems) are able to deliver changes with the input voltage considerably. With wide-range mains, at maximum line it can be more than twice the value at minimum line, as shown by the upper curve in the diagram of Figure 16 on page 28. The device has the line feedforward function available to solve this issue. It acts on the overcurrent setpoint Vcsx, so that it is a function of the converter's input voltage Vin sensed through a dedicated pin (15, VFF): the higher the input voltage, the lower the
27/51
Application information
L6566B
setpoint. This is illustrated in the diagram on the left-hand side of Figure 17 on page 29: it shows the relationship between the voltage on the pin VFF and Vcsx (with the error amplifier saturated high in the attempt of keeping output voltage regulation):
Equation 5
Vcsx = 1 -
VVFF k = 1 - Vin 3 3
Figure 16. Typical power capability change vs input voltage in QR flyback converters
2.5
k=0
2
system not compensated
inmin V inlim @ P
1.5
k
1
system optimally compensated
k = kopt
0.5 1 1.5 2 2.5 3 3.5 4
Vin Vinmin
Note:
If the voltage on the pin exceeds 3 V switching ceases but the soft-start capacitor is not discharged. The schematic in Figure 17 on page 29 shows also how the function is included in the control loop.
With a proper selection of the external divider R1-R2, i.e. of the ratio k = R2 / (R1+R2), it is possible to achieve the optimum compensation described by the lower curve in the diagram of Figure 16. The optimum value of k, kopt, which minimizes the power capability variation over the input voltage range, is the one that provides equal power capability at the extremes of the range. The exact calculation is complex, and non-idealities shift the real-world optimum value from the theoretical one. It is therefore more practical to provide a first cut value, simple to be calculated, and then to fine tune experimentally. Assuming that the system operates exactly at the boundary between DCM and CCM, and neglecting propagation delays, the following expression for kopt can be found:
Equation 6
k opt = 3
Vin min Vin max
VR + (Vin min + Vin max ) VR
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L6566B
Application information
Experience shows that this value is typically lower than the real one. Once the maximum peak primary current, IPKpmax, occurring at minimum input voltage Vinmin has been found, the value of Rs can be determined from (5):
Equation 7
Rs =
1-
k opt 3
Vin min
IPKp max
Figure 17. Left: overcurrent setpoint vs VFF voltage; right: line feedforward function block
Rectif ied Line Voltage
Vcsx [V]
1.2
VCOMP= Upper clamp
R1
Optional for OVP settings
1
0.8
R2 VFF 15 CS 7 VOLTAGE FEED FORWARD 9 + PWM
Rs
0.6
0.4 COMP 0.2
R Q S
Clock/ZCD
4
DRIVER
The converter is then tested on the bench to find the output power level Poutlim where regulation is lost (because overcurrent is being tripped) both at Vin = Vinmin and Vin = Vinmax. If Poutlim @ Vinmax > Poutlim @ Vinmin the system is still undercompensated and k needs increasing; if Poutlim @ Vinmax < Poutlim @ Vinmin the system is overcompensated and k needs decreasing. This will go on until the difference between the two values is acceptably low. Once found the true kopt in this way, it is possible that Poutlim turns out slightly different from the target; to correct this, the sense resistor Rs needs adjusting and the above tuning process will be repeated with the new Rs value. Typically a satisfactory setting is achieved in no more than a couple of iterations. In applications where this function is not wanted, e.g. because of a narrow input voltage range, the VFF pin can be simply grounded, directly or through a resistor (see "Section 5.11: OVP block on page 35"). The overcurrent setpoint will be then fixed at the maximum value of 1V. If a lower setpoint is desired to reduce the power dissipation on Rs, the pin can be also biased at a fixed voltage using a divider from VREF (pin 10). If the FF option is selected the line feedforward function can be still used to compensate for the total propagation delay Td of the current sense chain (internal propagation delay td(H-L) plus the turn-off delay of the external MOSFET), which in standard current mode PWM controllers is done by adding an offset on the current sense pin proportional to the input voltage. In that case the divider ratio k, which will be much smaller as compared to that used with the QR option selected, can be calculated with the following equation:
-
VVFF [V]
L6566B
1.5 V
+
0
Vcsx
0 0.5 1 1.5 2 2.5 3 3.5
Hiccup
+ OCP -
GD
DISABLE
29/51
Application information Equation 8
L6566B
k opt = 3
Td Rs Lp
where Lp is the inductance of the primary winding. In case a constant maximum power capability vs. the input voltage is not required, the VFF pin can be grounded, directly or through a resistor (see Section 5.11: OVP block on page 35), hence fixing the overcurrent setpoint at 1 V, or biased at a fixed voltage through a divider from VREF to get a lower setpoint. It is possible to bypass the pin to ground with a small film capacitor (e.g. 1-10 nF) to ensure a clean operation of the IC even in a noisy environment. The pin is internally forced to ground during UVLO, after activating any latched protection and when pin COMP is pulled below its low clamp voltage (see Section 5.5: PWM control block on page 26).
5.7
Hiccup-mode OCP
A third comparator senses the voltage on the current sense input and shuts down the device if the voltage on the pin exceeds 1.5 V, a level well above that of the maximum overcurrent setpoint (1 V). Such an anomalous condition is typically generated by either a short circuit of the secondary rectifier or a shorted secondary winding or a hard-saturated flyback transformer.
Figure 18. Hiccup-mode OCP: timing diagram
Vcc (pin 5)
VccON VccOFF Vccrestart
Secondary diode is shorted here
VCS (pin 7)
1.5 V
t
GD (pin 4) OCP latch
t
t t
Vcc_OK
t
To distinguish an actual malfunction from a disturbance (e.g. induced during ESD tests), the first time the comparator is tripped the protection circuit enters a "warning state". If in the next switching cycle the comparator is not tripped, a temporary disturbance is assumed and the protection logic will be reset in its idle state; if the comparator will be tripped again a real malfunction is assumed and the L6566B will be stopped. Depending on the time relationship
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L6566B
Application information
between the detected event and the oscillator, occasionally the device could stop after the third detection. This condition is latched as long as the device is supplied. While it is disabled, however, no energy is coming from the self-supply circuit; hence the voltage on the Vcc capacitor will decay and cross the UVLO threshold after some time, which clears the latch. The internal start-up generator is still off, then the Vcc voltage still needs to go below its restart voltage before the Vcc capacitor is charged again and the device restarted. Ultimately, this will result in a low-frequency intermittent operation (Hiccup-mode operation), with very low stress on the power circuit. This special condition is illustrated in the timing diagram of Figure 18 on page 30.
5.8
Frequency modulation
To alleviate converter's EMI emissions and reduce cost and size of the line filter, it is advantageous to modulate its switching frequency, so that the resulting spread-spectrum action distributes the energy of each harmonic of the switching frequency over a number of side-band harmonics. Their overall energy will be unchanged but the individual amplitudes will be smaller. This is what naturally occurs with QR operation, due to the twice-mainsfrequency ripple appearing on the input bulk capacitor, which translates into different DCMCCM boundary frequencies. The L6566B is provided with a dedicated pin, FMOD (6), to perform this function if FF mode is selected.
Figure 19. Frequency modulation circuit
L6566B
13 1V 6 1.5 V
OSC
0V
FMOD RMOD
0.5 V
RT
CMOD
With reference to Figure 19, the capacitor CMOD is connected from FMOD to ground and is alternately charged and discharged between 0.5 and 1.5 V by internal current generators sourcing and sinking the same current (three times the current defined by the resistor RT on pin OSC). Hence, the voltage across CMOD will be a symmetric triangle, whose frequency fm is determined by CMOD. By connecting a resistor RMOD from FMOD to OSC, the current sourced by pin OSC will be modulated according a triangular profile at a frequency fm. If RMOD is considerably higher than RT, as normally is, both fm and the symmetry of the triangle will be little affected. With this arrangement it is possible to set, nearly independently, the frequency deviation fsw and the modulating frequency fm, which define the modulation index:
31/51
Application information Equation 9
L6566B
=
fsw fm
which is the parameter that the amplitude of the generated side-band harmonics depends on. The minimum frequency fsw_min (occurring on the peak of the triangle) and the maximum frequency fsw_max (occurring on the valley of the triangle) will be symmetrically placed around the centre value fsw, so that:
Equation 10
1 fsw _ min = fsw - 2 fsw ; 1 fsw _ max = fsw + 2 fsw
Then, RT will be found from (5) (see Section 5.2: Zero current detection and triggering block; oscillator block on page 21), while RMOD and CMOD can be calculated as follows:
Equation 11
R MOD =
2 10 3 fsw
C MOD =
75 fm
where fsw and fm (in kHz, with CMOD in nF and RMOD in k) will be selected by the user so to achieve the best compromise between attenuation of peak EMI emissions and clean converter operation.
5.9
Latched disable function
The device is equipped with a comparator having the non-inverting input externally available at the pin DIS (8) and with the inverting input internally referenced to 4.5 V. As the voltage on the pin exceeds the internal threshold, the device is immediately shut down and its consumption reduced to a low value. The information is latched and it is necessary to let the voltage on the Vcc pin go below the UVLO threshold to reset the latch and restart the device. To keep the latch supplied as long as the converter is connected to the input source, the HV generator is activated periodically so that Vcc oscillates between the start-up threshold VccON and VccON - 0.5 V. Activating the HV generator in this way cuts its power dissipation approximately by three (as compared to the case of continuous conduction) and keeps peak silicon temperature close to the average value. To let the L6566B restart it is then necessary to disconnect the converter from the input source. Pulling pin 16 (AC_OK) below the disable threshold (see Section 5.12: Brownout protection on page 37) will stop the HV generator until Vcc falls below Vccrestart, so that the latch can be cleared and a quicker restart is allowed as the input source is removed. This operation is shown in the timing diagram of Figure 20 on page 33.
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L6566B
Application information
This function is useful to implement a latched overtemperature protection very easily by biasing the pin with a divider from VREF, where the upper resistor is an NTC physically located close to a heating element like the MOSFET, or the transformer. The DIS pin is a high impedance input, thus it is prone to pick up noise, which might give origin to undesired latch-off of the device. It is possible to bypass the pin to ground with a small film capacitor (e.g. 1-10 nF) to prevent any malfunctioning of this kind.
Figure 20. Operation after latched disable activation: timing diagram
DIS (pin 8)
4.5V
Vcc (pin 5)
VccON VccON -0.5 VccOFF Vccrestart
HV generator is turned on
Restart is quicker
t
Disable latch is reset here
GD (pin 4)
HV generator turn-on is disabled here
t
Vin
VHVstart
Input source is removed here
t
AC_OK (pin 16)
Vth
t
t
5.10
Soft-start and delayed latched shutdown upon overcurrent
At device start-up, a capacitor (CSS) connected between the SS pin (14) and ground is charged by an internal current generator, ISS1, from zero up to about 2 V where it is clamped. During this ramp, the overcurrent setpoint progressively rises from zero to the value imposed by the voltage on the VFF pin (15, see Section 5.6: PWM comparator, PWM latch and voltage feedforward blocks on page 27); MOSFET's conduction time increases gradually, hence controlling the start-up inrush current. The time needed for the overcurrent setpoint to reach its steady state value, referred to as soft-start time, is approximately:
Equation 12
TSS =
V Css Css 1 - VFF Vcsx (VVFF ) = ISS1 ISS1 3
During the ramp (i.e. until VSS = 2 V) all the functions that monitor the voltage on pin COMP are disabled.
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Application information
L6566B
The soft-start pin is also invoked whenever the control voltage (COMP) saturates high, which reveals an open-loop condition for the feedback system. This condition very often occurs at start-up, but may be also caused by either a control loop failure or a converter overload/short circuit. A control loop failure results in an output overvoltage that is handled by the OVP function of the L6566B (see next section). In case of QR operation, a short circuit causes the converter to run at a very low frequency, then with very low power capability. This makes the self-supply system that powers the device unable to keep it operating, so that the converter will work intermittently, which is very safe. In case of overload the system has a power capability lower than that at nominal load but the output current may be quite high and overstress the output rectifier. In case of FF operation the capability is almost unchanged and both short circuit and overload conditions are more critical to handle. The L6566B, regardless of the operating option selected, makes it easier to handle such conditions: the 2 V clamp on the SS pin is removed and a second internal current generator ISS2 = ISS1 /4 keeps on charging CSS. As the voltage reaches 5 V the device is disabled, if it is allowed to reach 2 VBE over 5 V, the device will be latched off. In the former case the resulting behavior will be identical to that under short circuit illustrated in Figure 7 on page 20; in the latter case the result will be identical to that of Figure 20 on page 33. See Section 5.9: Latched disable function on page 32 for additional details.
Figure 21. Soft-start pin operation under different operating conditions and settings
Vcc (pin 5)
Vcc falls below UVLO before latching off
UVLO
SS (pin 14)
2V
5V+2Vbe 5V
t
here the IC shuts down here the IC latches off
COMP (pin 9)
t
GD (pin 4)
t
t
START-UP NORMAL OPERATION TEMPORARY OVERLOAD NORMAL OPERATION OVERLOAD SHUTDOWN
LATCHED AUTORESTART
RESTART
A diode, with the anode to the SS pin and the cathode connected to the VREF pin (10) is the simplest way to select either auto-restart mode or latch-mode behavior upon overcurrent. If the overload disappears before the Css voltage reaches 5 V the ISS2 generator will be turned off and the voltage gradually brought back down to 2 V. Refer to the "Application examples and Ideas" section (Table 7 on page 45) for additional hints. If latch-mode behavior is desired also for converter's short circuit, make sure that the supply voltage of the device does not fall below the UVLO threshold before activating the latch. Figure 21 shows soft-start pin behavior under different operating conditions and with different settings (latch-mode or autorestart).
Note: Unlike other PWM controllers provided with a soft-start pin, in the L6566B grounding the SS pin does not guarantee that the gate driver is disabled.
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L6566B
Application information
5.11
OVP block
The OVP function of the L6566B monitors the voltage on the ZCD pin (11) in MOSFET's OFF-time, during which the voltage generated by the auxiliary winding tracks converter's output voltage. If the voltage on the pin exceeds an internal 5 V reference, a comparator is triggered, an overvoltage condition is assumed and the device is shut down. An internal current generator is activated that sources 1 mA out of the VFF pin (15). If the VFF voltage is allowed to reach 2 Vbe over 5 V, the L6566B will be latched off. See Section 5.9: Latched disable function on page 32 for more details on IC's behavior under these conditions. If the impedance externally connected to pin 15 is so low that the 5+2 VBE threshold cannot be reached or if some means is provided to prevent that, the device will be able to restart after the Vcc has dropped below 5 V. Refer to the "Application examples and Ideas" section (Table 7 on page 45) for additional hints.
Figure 22. OVP function: internal block diagram
ZCD
to triggering block
11
5V 40k +
L6566B
COUT
PWM latch
5pF
R S
Q
OVP
Q
Monostable M1
Monostable M2
2 s
STROBE
0.5 s
2-bit counter FF R Q1 S
Fault
Counter reset
The ZCD pin will be connected to the auxiliary winding through a resistor divider RZ1, RZ2 (see Figure 8 on page 20). The divider ratio kOVP = RZ2 / (RZ1 + RZ2) will be chosen equal to:
Equation 13
k OVP =
5 Ns Vout OVP Naux
where VoutOVP is the output voltage value that is to activate the protection, Ns the turn number of the secondary winding and Naux the turn number of the auxiliary winding.
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Application information Figure 23. OVP function: timing diagram
GD (pin 4)
L6566B
Vaux
0
t
ZCD (pin 11)
5V
t
COUT
t t
STROBE
2 s
0.5 s
OVP
t
COUNTER RESET COUNTER STATUS FAULT
t
t
0 0 0 0 1 1 2 2 0 0 0 1 1 2 2 3 3 4
t t
NORMAL OPERATION
TEMPORARY DISTURBANCE
FEEDBACK LOOP FAILURE
The value of RZ1 will be such that the current sourced by the ZCD pin be within the rated capability of the internal clamp:
Equation 14
R Z1
1 3 10
-3
Naux Vin max Np
where Vinmax is the maximum dc input voltage and Ns the turn number of the primary winding. See Section 5.2: Zero current detection and triggering block; oscillator block on page 21 for additional details. To reduce sensitivity to noise and prevent the latch from being erroneously activated, first the OVP comparator is active only for a small time window (typically, 0.5 s) starting 2 s after MOSFET's turn-off, to reject the voltage spike associated to the positive-going edges of the voltage across the auxiliary winding Vaux; second, to stop the L6566B the OVP comparator must be triggered for four consecutive switching cycles. A counter, which is reset every time the OVP comparator is not triggered in one switching cycle, is provided to this purpose.
Figure 22 on page 35 shows the internal block diagram, while the timing diagrams in Figure 23 illustrate the operation. Note: To use the OVP function effectively, i.e. to ensure that the OVP comparator will be always interrogated during MOSFET's OFF-time, the duty cycle D under open-loop conditions must fulfill the following inequality:
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L6566B Equation 15
Application information
D + TBLANK 2 fsw 1 where TBLANK2 = 2 s; this is also illustrated in the diagram of Figure 24.
Figure 24. Maximum allowed duty cycle vs switching frequency for correct OVP detection
0.8 0.725 0.7 0.6
Dmax
0.5 0.4 0.3 0.2 5 .10
4
1 . 10
5
1.5 . 10
5
2 . 10
5
2.5 .10
5
3 . 10
5
3.5 .10
5
4 . 10
5
fsw [Hz]
5.12
Brownout protection
Brownout protection is basically a not-latched device shutdown function activated when a condition of mains undervoltage is detected. There are several reasons why it may be desirable to shut down a converter during a brownout condition, which occurs when the mains voltage falls below the minimum specification of normal operation. Firstly, a brownout condition may cause overheating of the primary power section due to an excess of RMS current. Secondly, spurious restarts may occur during converter power down, hence causing the output voltage not to decay to zero monotonically. L6566B shutdown upon brownout is accomplished by means of an internal comparator, as shown in the block diagram of Figure 25 on page 38, which shows the basic usage. The inverting input of the comparator, available on the AC_OK pin (16), is supposed to sense a voltage proportional to the RMS (peak) mains voltage; the non-inverting input is internally referenced to 0.485 V with 35 mV hysteresis. If the voltage applied on the AC_OK pin before the device starts operating does not exceed 0.485 V or if it falls below 0.45 V while the device is running, the AC_FAIL signal goes high and the device shuts down, with the softstart capacitor discharged and the gate-drive output low. Additionally, if the device has been latched off by some protection function (testified by Vcc oscillating between VccON and VccON - 0.5 V) the AC_OK voltage falling below 0.45 V clears the latch. This may allow a quicker restart as the input source is removed. While the brownout protection is active the start-up generator keeps on working but, being there no PWM activity, the Vcc voltage continuously oscillates between the start-up and the HV generator restart thresholds, as shown in the timing diagram of Figure 25.
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Application information Figure 25. Brownout protection: internal block diagram and timing diagram
L6566B
Sensed voltage
VsenON VsenOFF
VAC_OK (pin 16)
0.485V 0.45V t
Sensed voltage
Vcc
AC_FAIL
5
t
L6566B
RH
AC_OK
16 15 A 0.485V 0.45V
IHYS
15 A
t
AC_FAIL
+
Vcc (pin 5)
t
RL
GD (pin 4) Vout
t
t
t
The brownout comparator is provided with current hysteresis in addition to voltage hysteresis: an internal 15 A current sink is ON as long as the voltage applied on the AC_OK pin is such that the AC_FAIL signal is high. This approach provides an additional degree of freedom: it is possible to set the ON threshold and the OFF threshold separately by properly choosing the resistors of the external divider (see below). With just voltage hysteresis, instead, fixing one threshold automatically fixes the other one depending on the built-in hysteresis of the comparator. With reference to Figure 25, the following relationships can be established for the ON (VsenON) and OFF (VsenOFF) thresholds of the sensed voltage:
Equation 16
Vsen ON - 0.485 0.485 = 15 10 - 6 + RH RL which, solved for RH and RL, yield:
Equation 17
Vsen OFF - 0.45 0.45 = RH RL
RH =
Vsen ON - 1.078 Vsen OFF 15 10
-6
;
RL = RH
0.45 Vsen OFF - 0.45
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L6566B
Application information Figure 26. Voltage sensing techniques to implement brownout protection with the L6566B
HV Input bus AC mains (L/N)
AC mains (N/L) RH
AC_OK
16
RH
AC_OK
16
RH
RL1 RL RL2
L6566B
RL
RL1
VFF
L6566B
15
VFF
15
RL2 CF
Optionalfor OVPsettings
Optionalfor OVP settings
a)
b)
It is typically convenient to use a single divider to bias both the AC_OK and the VFF pins, as shown in Figure 26: this is possible because in all practical cases the voltage on the VFF pin is lower than that on the AC_OK pin. Once RH and RL have been found as suggested above, and kopt, either calculated from (6) or (8) or experimentally found, RL will be split as:
Equation 18
R L 2 = k opt ( R L + R H ) ; R L1 = R L - R L 2
Circuit a) senses the input voltage bus (across the bulk capacitor, downstream the bridge rectifier); in this case, for a proper operation of the brownout function, VsenON must be lower than the peak voltage at minimum mains and VsenOFF lower than the minimum voltage on the input bulk capacitor at minimum mains and maximum load considering, in case, holdup requirements during mains missing cycles as well. Brownout level will be load-dependent. In case of latched shutdown, when the input source is removed it is necessary to wait until the bulk capacitor voltage falls below the start voltage of the HV generator VHVstart in order for the unit to restart, which may take even several seconds. Circuit b) senses the mains voltage directly, upstream the bridge rectifier. It can be configured either for half-wave sensing (only the line/neutral wire is sensed) or full-wave sensing (both neutral and line are sensed); in the first case, assuming CF is large enough, the sensed voltage will be equal to 1/ the peak mains voltage, while in the second case it will be equal to 2/ the peak mains voltage. CF needs to be quite a big capacitor (in the uF) to have small residual ripple superimposed on the dc level; as a rule-of-thumb, use a time constant RL *CF at least 4-5 times the maximum line cycle period in case of half-wave sensing, 2-3 times in case of full-wave sensing. Then fine tune if needed, considering also transient conditions such as mains missing cycles. Brownout level will not depend on the load. When the input source is removed CF will be discharged after some ten ms then this circuit is suitable to have a quick restart after a latched shutdown. The AC_OK pin is a high impedance input connected to high value resistors, thus it is prone to pick up noise, which might alter the OFF threshold when the converter is running or give origin to undesired switch-off of the device during ESD tests. It is possible to bypass the pin to ground with a small film capacitor (e.g. 1-10 nF) to prevent any malfunctioning of this kind. The voltage on the pin is clamped upwards at about 3.15 V; then, if the function is not used the pin has to be connected to Vcc through a resistor (220 to 680 k).
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Application information
L6566B
5.13
Slope compensation
The pin MODE/SC (12), when not connected to VREF, provides a voltage ramp during MOSFET's ON-time synchronous to that of the internal oscillator sawtooth, with 0.8 mA minimum current capability. This ramp is intended for implementing additive slope compensation on current sense. This is needed to avoid the sub-harmonic oscillation that arises in all peak-current-mode-controlled converters working at fixed frequency in continuous conduction mode with a duty cycle close to or exceeding 50 %.
Figure 27. Slope compensation waveforms
Internal oscillator
GD (pin 4)
t
MODE/SC (pin 12)
t
t
The compensation will be realized by connecting a programming resistor between this pin and the current sense input (pin 7, CS). The CS pin has to be connected to the sense resistor with another resistor to make a summing node on the pin. Since no ramp is delivered during MOSFET OFF-time (see Figure 27), no external component other than the programming resistor is needed to ensure a clean operation at light loads.
Note: The addition of the slope compensation ramp will reduce the available dynamics of the current signal; thereby, the value of the sense resistor must be determined taking this into account. Note also that the burst-mode threshold (in terms of power) will be slightly changed.
If slope compensation is not required with FF operation, the pin shall be left floating.
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L6566B
Application information
5.14
Summary of L6566B power management functions
It has been seen that the device is provided with a number of power management functions: multiple operating mode upon loading conditions and protection functions. To help the designer familiarize with these functions, in the following tables all of theme are summarized with their respective activation mechanism and the resulting status of the most important pins. This can be useful not only for a correct use of the IC but also for diagnostic purposes: especially at prototyping/debugging stage, it is quite common to bump into unwanted activation of some function, and these tables can be used as a sort of quick troubleshooting guide.
Table 5.
L6566B light load management features
Caused by IC behavior Vcc_restart Consump. VREF (V) (Iqdis,mA) (V) SS VCOMP (V) OSC (V) FMOD
Feature Description
Burst mode
Controlled ON-OFF Pulse operation for VCOMP < low power VCOMPBM skipping operation consumptio - Hys n at light load
N.A.
1.34 mA
5
unchanged
VCOMPBM -HYS to VCOMPBM
0/1
0
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Application information
L6566B
Table 6.
Protection
L6566B protections
Description Caused by Vcc IC Iq VREF IC restart behavior (mA) (V) (V) SS VCOMP (V) OSC (V) FMOD VFF
OVP
VZCD>VZCDt h for 4 Auto consecutive Output restart(1) overvoltage switching protection cycles VFF > VFFlatch VCOMP =VCOMPHi Output overload protection VSS > VSSDIS VCOMP =VCOMPHi VSS > VSSLAT VCOMP =VCOMPHi Latched
5
2.2
5(6)
unchanged
(6)
0
0
0
unchanged
13.5
0.33
0
0
0
0
0
0
Auto restart(2)
5
1.46
5(6)
VSS VCOMPHi (6) 0
0
unchanged
OLP
Latched
13.5
0.33
0
0
0
0
0
0
VSS > Output short VSSDIS(4) Short circuit circuit protection protection VCOMP =VCOMPHi VSS > VSSLAT(6) Transformer saturation or shorted secondary diode protection Externally settable overtempera ture protection Internal thermal shutdown Brownout Reference drift Shutdown1 Mains undervoltag e protection VREF drift protection Gate driver disable VCS > VCSDIS for 2-3 consecutive switching cycles
Auto restart
5
1.46
0
VSS VCOMPHi (5) 0
unchanged
Latched
13.5
0.33
0
0
0
0
0
0
2nd OCP
Latched
5
0.33
0
0
0
0
0
0
VDIS>VOTP
Latched
13.5
0.33
0
0
0
0
0
0
OTP
Tj > 160oC
Auto restart(5)
5
0.33
0
0
0
0
0
0
VAC_OK < Vth VREF > Vov VFF > Voff
Auto restart Latched Auto restart
5
0.33
0
0
0
0
0
unchanged
13.5 5
0.33 2.5
0 5
0 unchanged
0 unchang ed
0 1
0 uncha nged
0 unchanged
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L6566B Table 6.
Protection
Application information L6566B protections (continued)
Description Caused by Vcc IC Iq VREF IC restart behavior (mA) (V) (V) SS VCOMP (V) OSC (V) FMOD VFF
Shutdown2
Shutdown by VCOMP low Shutdown by Vcc going below Vccoff (lowering of Vccoff threshold at light load)
VCOMP < VCOMPOFF Vcc < 9.4V (VCOMP > VCOMPL) Vcc < 7.2V (VCOMP > VCOMPO)
Latched
10
0.33
0
0
0
0
0
0
ADAPTIVE UVLO
Auto restart
5V
0.18 mA
0
0
0
0
0
0
1. Use One external diode from VFF (#15) to AC_OK (#16), cathode to AC_OK 2. Use one external diode from SS (#14) to VREF (#10), cathode to VREF 3. If Css and the Vcc capacitor are such that Vcc falls below UVLO before latch tripping (Figure 21 on page 34) 4. If Css and the Vcc capacitor are such that the latch is tripped before Vcc falls below UVLO (Figure 21 on page 34) 5. When TJ < 110 oC 6. Discharged to zero by Vcc going below UVLO
It is worth reminding that "Auto-restart" means that the device will work intermittently as long as the condition that is activating the function is not removed; "Latched" means that the device is stopped as long as the unit is connected to the input power source and the unit must be disconnected for some time from the source in order for the device (and the unit) to restart. Optionally, a restart can be forced by pulling the voltage of pin 16 (AC_OK) below 0.45 V.
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Application examples and ideas
L6566B
6
Application examples and ideas
Figure 28. Typical low-cost application schematic
F1 fuse
Vin 88 to 264 Vac NTC1 B1
CY1 CX1 Lx CY2 CX2
T1 C1
R1
C2 D4 Vout
D1
C8A,B R3 470k C3 FMOD DIS 8 VFF 15 6 AC_OK 16 1 HVS 5 4 GD R4 Q1 D3 7 9 COMP 3 GND 11 CS ZCD 4 R5 R9 3 IC3 1 R7 Vcc R2 D2 C7 2.2 nF Y1
IC1
L6566B
12 MODE/SC 10 VREF 13 OSC 14 SS
2
C9
R8
Optional f or QR operation
C4 R6
C5
C6
Optional f or QR operation
TL431 R10
Figure 29. Typical full-feature application schematic (QR operation)
F1 fuse
Vin 88 to 264 Vac NTC1 B1
CY1 CX1 Lx CY2 CX2
T1 C1
R1
C2 D4 Vout
D1
C8A,B R2 D2 1N4148 C7 2.2 nF Y1 ZCD GD R3 R4 Q1 D3 1N4148 7 14 SS 9 COMP 3 R18 R13 NTC2 VREF MODE/SC OSC GND 3 2 C9 R8 CS R5 IC3 PC817A 4 10 6 12 13 R9 1 R7
R15 FMOD AC_OK 16 R14 VFF DIS 15 8 6 1 HVS 5 Vcc 11 4
C3
IC1
L6566B
R12
C4
R6
C5
C6
TL431 R10
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L6566B
Application examples and ideas
Figure 30. Typical full-feature application schematic (FF operation)
F1 fuse
Vin 88 to 264 Vac NTC1 B1
CY1 CX1 Lx CY2 CX2
T1 C1
R1
C2 D4 Vout
D1
C8A,B R2 R16 R15 MODE/SC AC_OK 16 R14 VFF DIS 15 8 10 R13 NTC2 VREF 6 FMOD R11 13 OSC 14 SS 9 COMP 3 GND R18 3 2 C9 R8 12 1 HVS 5 Vcc 11 4 ZCD GD R3 R4 Q1 D3 1N4148 7 CS R17 R5 IC3 PC817A 4 R9 1 R7 C3 D2 1N4148 C7 2.2 nF Y1
IC1
L6566B
R12
C10 C4 R6 C5 C6 TL431 R10
Table 7.
External circuits that determine IC behavior upon OVP and OCP
OVP latched OVP auto-restart
RH
AC_OK
SS
14 16
VREF
10
RH
AC_OK
SS
14 16
VREF
10
OCP latched
RL1 RL2 RFF
VFF
L6566B
15
RL1 RL2
VFF
15
L6566B
3.3 + 1.3 10 -3 RL1 6. 4 R 1 + L1 RL 2
RFF 10 RL2
Diode needed if
1N4148
1N4148
RH
AC_OK
SS
14 16
VREF
10
RH
AC_OK
SS
14 16
VREF
10
OCP auto-restart
RL1 RL2 RFF
VFF
L6566B
15
RL1 RL2
VFF
15
L6566B
Diode needed if
3.3 + 1.3 10 -3 RL1 6.4 R 1 + L1 RL 2
45/51
Application examples and ideas Figure 31. Frequency foldback at light load (FF operation)
R1 MODE/SC 12 Vref 10 COMP 9 BC857C R2
L6566B
L6566B
13 OSC RT
Figure 32. Latched shutdown upon mains overvoltage
Vin Vin
Vcc 5 BC847
BC857 Vref
L6566B
8
DIS
DIS 8 >10 Rq
10
15
VFF
L6566B
Rq 15 VFF
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L6566B
Package mechanical data
7
Package mechanical data
In order to meet environmental requirements, ST offers these devices in ECOPACK(R) packages. These packages have a lead-free second level interconnect. The category of second Level Interconnect is marked on the package and on the inner box label, in compliance with JEDEC Standard JESD97. The maximum ratings related to soldering conditions are also marked on the inner box label. ECOPACK is an ST trademark. ECOPACK specifications are available at: www.st.com.
47/51
Package mechanical data Table 8.
Dim. Min A a1 0.1 Typ Max 1.75 0.25 0.004 Min Typ
L6566B
SO16N mechanical data
mm. inch Max 0.069 0.009
a2 b b1 C c1
D
1.6 0.35 0.19 0.5 45 9.8 5.8 1.27 8.89 3.8 4.60 0.4 4.0 5.30 1.27 0.150 0.181 0.150 10 6.2 (typ.) 0.386 0.228 0.050 0.350 0.46 0.25 0.014 0.007 0.020
0.063 0.018 0.010
0.394 0.244
E e e3
F
0.157 0.208 0.050
G L
M S
0.62 8(max.)
0.024
Figure 33. Package dimensions
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L6566B
Order codes
8
Order codes
Table 9. Order codes
Order codes L6566B L6566BTR Package SO16N SO16N Packaging Tube Tape and reel
49/51
Revision history
L6566B
9
Revision history
Table 10.
Date 20-Aug-2007 29-May-2008
Document revision history
Revision 1 2 First release Updated Figure 29 on page 44, Table 2 on page 11 Changes
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L6566B
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