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Product Specification Low-Cost, Green-Mode PWM Controller for Flyback Converters SG6858
FEATURES
Green-mode PWM Supports the "Blue Angel" standard Low start-up current (10A) Low operating current (2.5mA) Leading-edge blanking Constant output power limit Universal input Built-in synchronized slope compensation Current-mode operation Cycle-by-cycle current limiting Under voltage lockout (UVLO) Programmable PWM frequency VDD over-voltage protection (auto restart) Gate output voltage clamped at 17V Low cost Few external components required Small SOT-26 and DIP-8 packages
DESCRIPTION
This highly integrated PWM controller provides several special enhancements designed to meet the low standby power needs of low-power SMPS. To minimize standby power consumption, the proprietary green-mode function provides off-time modulation to linearly decrease the switching frequency under light-load conditions. This green-mode function enables the power supply to meet even the strictest power conservation requirements. The BiCMOS fabrication process enables reducing the start-up current to 10A and the operating current to 2.5mA. To further improve power conservation, a large start-up resistance can be used. Built-in synchronized slope compensation ensures the stability of peak current mode control. Proprietary internal compensation provides a constant output power limit over a universal AC input range (90VAC to 264VAC). Pulse-by-pulse current limiting ensures safe operation even during short-circuits. To protect the external power MOSFET from being damaged by supply over-voltage events, the SG6858's output driver is clamped at 17V. SG6858 controllers can be used to improve the performance and reduce the production cost of power supplies and can replace linear and RCC-mode power adapters. It is available in 8-pin DIP and 6-pin SOT-26 packages.
APPLICATIONS
General-purpose, switching-mode power supplies and flyback power converters, such as: Battery chargers for cellular phones, cordless phones, PDAs, digital cameras, and power tools Power adapters for ink jet printers, video game consoles, and portable audio players Open-frame SMPS for TV/DVD standby and auxiliary supplies, home appliances, and consumer electronics Replacements for linear transformers and RCC SMPS PC 5V standby power
TYPICAL APPLICATION
(c) System General Corp. Version 1.2.1 (IAO33.0045.B2)
-1-
www.sg.com.tw * www.fairchildsemi.com September 25, 2007
Product Specification Low-Cost, Green-Mode PWM Controller for Flyback Converters SG6858
MARKING DIAGRAMS
AAI: SG6858 m: Mask Version w: Week code A~Z=W1~W26 A~Z=W27~W52 : Lead Free Package
PIN CONFIGURATION
SOT-26 GND FB RI DIP-8 D: D=DIP P: Z=Lead Free Null=Regular Package XXXXXXXX: Wafer Lot Y: Year; WW: Week V: Assembly Location GATE VDD NC SENSE GND FB NC RI GATE VDD SENSE
AAImw
SG6858DP
XXXXXXXXYWWV
ORDERING INFORMATION
Part Number
SG6858TZ SG6858DZ
Pb-Free
Package
6-pin SOT-26 8-pin DIP-8
PIN DESCRIPTIONS
Name
GATE VDD NC SENSE
Pin No. DIP-8 SOT-26
1 2 3 4 4 6 5
Type
Driver Output Supply No Connection Analog Input
Function
The totem-pole output driver for driving the power MOSFET. Power supply. NC pin. Current sense. This pin senses the voltage across a resistor. When the voltage reaches the internal threshold, PWM output is disabled. This activates over-current protection. This pin also provides current amplitude information for current-mode control. A resistor connected from the RI pin to ground generates a constant current source used to charge an internal capacitor and determines the switching frequency. Increasing the resistance reduces the amplitude of the current source and reduce the switching frequency. A 95k resistor, RI, results in a 50A constant current II and a 70kHz switching frequency. NC pin. Feedback. The FB pin provides the output voltage regulation signal. It provides feedback to the internal PWM comparator, so that the PWM comparator can control the duty cycle. Ground.
RI
5
3
Analog Input/Output
NC FB GND
6 7 8 2 1
No Connection Analog Input Supply
(c) System General Corp. Version 1.2.1 (IAO33.0045.B2)
-2-
www.sg.com.tw * www.fairchildsemi.com September 25, 2007
Product Specification Low-Cost, Green-Mode PWM Controller for Flyback Converters SG6858
BLOCK DIAGRAM
(c) System General Corp. Version 1.2.1 (IAO33.0045.B2)
-3-
www.sg.com.tw * www.fairchildsemi.com September 25, 2007
Product Specification Low-Cost, Green-Mode PWM Controller for Flyback Converters SG6858
ABSOLUTE MAXIMUM RATINGS
Symbol
VVDD VFB VSENSE TJ R JA TSTG TL VESD-HBM VESD-MM
Parameter
DC Supply Voltage* Input Voltage to FB Pin Input Voltage to Sense Pin Operating Junction Temperature Thermal Resistance (Junction-to-Air) Storage Temperature Range Lead Temperature (Wave Soldering or Infrared, 10 Seconds) Electrostatic Discharge Capability, Human Body Model Electrostatic Discharge Capability, Machine Model
Value
30 -0.3 to 7.0 -0.3 to 7.0 -40 to +125 SOT DIP -55 to +150 260 3.0 200 208.4 82.5
Unit
V V V C C/W C/W C C kV V
* All voltage values, except differential voltages, are given with respect to GND pin. * Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device.
RECOMMENDED OPERATING CONDITIONS
Symbol
VDD TA
Parameter
DC Supply Voltage Operating Ambient Temperature
Value
22 -20 to +85
Unit
V C
* For proper operation.
ELECTRICAL CHARACTERISTICS
VDD=15V, TA = 25C, unless otherwise noted.
VDD Section
Symbol
VDD-OP VDD-ON VDD-OFF IDD-ST IDD-OP VDD-OVP tD-VDDOVP VDD-G OFF
Parameter
Continuously Operation Voltage Turn-on Threshold Voltage Turn-off Threshold Voltage Start-up Current Operating Supply Current VDD Over-Voltage Protection Level VDD Over-Voltage Protection Debounce VDD Low Threshold Voltage to Exit Green-off Mode
Test Condition
Min.
15.5 10.5
Typ.
16.5 11.5 10 2.5
Max.
22 17.5 12.5 15 3.5 26 200 VDD-OFF + 1.25
Unit
V V V A mA V s V
VDD=VDD-ON - 0.1V VDD=15V, GATE with 1nF to GND 24 50 VDD-OFF + 0.95
25 125 VDD-OFF + 1.10
(c) System General Corp. Version 1.2.1 (IAO33.0045.B2)
-4-
www.sg.com.tw * www.fairchildsemi.com September 25, 2007
Product Specification Low-Cost, Green-Mode PWM Controller for Flyback Converters SG6858
Feedback Input Section
Symbol
AV ZFB VFB-OPEN VFB-N VFB-G SG
Parameter
FB Input to Current Comparator Attenuation Input Impedance FB Output High Voltage Green-Mode Entry FB Voltage Green-Mode Ending FB Voltage Green-Mode Modulation Slope
Test Condition
Min.
Typ.
2/5 5
Max.
Unit
V/V K
4.5
5.0 2.85 2.20
5.5
V V V Hz/mV
RI=95k
75
Current-Sense Section
Symbol
ZSENSE tPD VSTHFL VSTHVA tLEB DCYSAW
Parameter
Input Impedance Delay to Output Flat Threshold Voltage for Current Limit Valley Threshold Voltage for Current Limit Leading-edge Blanking Time Duty Cycle of SAW Limit
Test Condition
Min.
10
Typ.
60 0.96
Max.
100 0.85 350
Unit
k ns V V ns %
0.75 250 Max. Duty Cycle
0.80 300 45
Oscillator Section
Symbol
FOSC FOSC-G FDV FDT
Parameter
Frequency Green-Mode Frequency Frequency Variation vs. VDD Deviation Frequency Variation vs. Temperature Deviation
Test Condition
RI=95k RI=95k VDD=13.5V to 22V TA= -20 to 85C
Min.
65 0
Typ.
70 22 0.02
Max.
75 2.00 2
Unit
kHz kHz % %
Output Section
Symbol
DCYMAX VGATE-L VGATE-H tR tF VGATE-CLAMP
Parameter
Maximum Duty Cycle Output Voltage Low Output Voltage High Rising Time Falling Time Output Clamp Voltage
Test Condition
VDD=15V, Io=20mA VDD=13.5V, Io=-20mA VDD=15V, CL=1nF VDD=15V, CL=1nF VDD=22V
Min.
70 8 150 35 16
Typ.
75
Max.
80 1.5
Unit
% V V ns ns V
200 55 17
250 75 18
(c) System General Corp. Version 1.2.1 (IAO33.0045.B2)
-5-
www.sg.com.tw * www.fairchildsemi.com September 25, 2007
Product Specification Low-Cost, Green-Mode PWM Controller for Flyback Converters SG6858
TYPICAL CHARACTERISTICS
Turn-On Threas hold Voltage (V DD-O N ) v s Tem perature
17.5 12.5 12.1
Turn-off Thres hold Voltage (V DD-O FF ) vs Temperature
17.0
V DD-O N (V)
V DD-O FF (V)
-40 -25 -10 5 20 35 50 65 80 95 110 125
16.5
11.7 11.3 10.9 10.5
16.0
15.5
Temperature ()
-40
-25
-10
5
Temperature ()
20
35
50
65
80
95
110
125
Startup Current(IDD-S T ) v s Tem perature
20
3.5
Operating Supply Current (IDD-O P ) v s Tem perature
15
3.0
IDD-S T (uA)
10
IDD-OP (m A)
2.5
5
2.0
VDD=15V
0 -40 -25 -10 5 20 35 50 65 80 95 110 125
1.5 -40 -25 -10 5 20 35 50 65 80
VDD=15V
95 110 125
Temperature ()
Temperature ()
Frequenc y (F O S C ) vs Tem perature
75 73 71 69 67 80 78
M ax im um Duty Cy c le (DCY MA X ) v s Tem perature
DCY MA X (%)
F O S C (KHz )
76 74 72
VDD=15V
65 -40 -25 -10 5 20 35 50 65 80 95 110 125 70 -40 -25 -10 5 20 35 50 65 80
VDD=15V
95 110 125
Temperature ()
Temperature ()
(c) System General Corp. Version 1.2.1 (IAO33.0045.B2)
-6-
www.sg.com.tw * www.fairchildsemi.com September 25, 2007
Product Specification Low-Cost, Green-Mode PWM Controller for Flyback Converters
Green-Mode Entry FB Voltage(V FB -N ) v s Temperature
3.2 3.1 3.0 2.9 2.8 2.7 2.6 2.5 -40 -25 -10 5 20 35 50 65 80 95 110 125
SG6858
Green-M ode Ending FB Voltage (V FB -G ) v s Temperature
2.50 2.40
V FB -G (V)
V FB -N (V)
2.30 2.20 2.10 2.00 1.90 -40 -25 -10 5 20 35 50 65 80 95 110 125
VDD=15V
VDD=15V
Temperature ()
Tem perature ()
Leading-Edge Blank ing Time (t L E B ) vs Tem perature
350 330 310 290 270
Operation Current (IDD-OP) vs VDD Voltage
3.5
3.0
IDD-OP (m A)
t L E B (ns ec )
2.5
2.0
VDD=15V
250 -40 -25 -10 5 20 35 50 65 80 95 110 125
1.5 12 13 14 15 16 17 18 19 20 21 22 23 24
Temperature ()
VDD Voltage (V)
(c) System General Corp. Version 1.2.1 (IAO33.0045.B2)
-7-
www.sg.com.tw * www.fairchildsemi.com September 25, 2007
Product Specification Low-Cost, Green-Mode PWM Controller for Flyback Converters SG6858
OPERATION DESCRIPTION
SG6858 devices integrate many useful designs into one controller for low-power switch-mode power supplies. The following descriptions highlight some of the features of the SG6858 series. frequency. The relationship between RI and the switching frequency is:
fPWM =
6650 R I (k )
(kHz )
(1)
Start-up Current
The start-up current is only 10A, which allows a start-up resistor with a high resistance and a low-wattage to supply the start-up power for the controller. A 1.5M, 0.25W, start-up resistor and a 10F/25V VDD hold-up capacitor are sufficient for an AC-to-DC power adapter with a wide input range (100VAC to 240VAC).
Leading-Edge Blanking
Each time the power MOSFET is switched on, a turn-on spike occurs at the sense-resistor. To avoid premature termination of the switching pulse, a 300ns leading-edge blanking time is built in. Conventional RC filtering can therefore be omitted. During this blanking period, the current-limit comparator is disabled and cannot switch off the gate driver.
Operating Current
The operating current has been reduced to 2.5mA. The low operating current results in higher efficiency and reduces the VDD hold-up capacitance requirement.
Constant Output Power Limit
When the SENSE voltage across the sense resistor, RS, reaches the threshold voltage (around 0.96V), the output GATE drive is turned off following a short propagation delay tPD. This propagation delay introduces additional current proportional to tPD*Vin/Lp. The propagation delay is nearly constant regardless of the input line voltage VIN. Higher input line voltages result in larger additional currents. At high input line voltages, the output power limit is higher than at low input line voltages. To compensate for this output power limit variation across a wide AC input range, the threshold voltage is adjusted by adding a positive ramp (VLIMIT_RAMP). This ramp signal rises from 0.80V to 0.96V, then flattens out at 0.96V. A smaller threshold voltage forces the output GATE drive to terminate earlier. This reduces the total PWM turn-on time and makes the output power equal to that of low line input. This proprietary internal compensation ensures a constant output power limit for a wide AC input voltage range (90VAC to 264VAC).
Green-Mode Operation
The proprietary green-mode function provides off-time modulation to linearly decrease the switching frequency under light-load conditions. On-time is limited to provide stronger protection against brownouts and other abnormal conditions. The feedback current, which is sampled from the voltage feedback loop, is taken as the reference. Once the feedback current exceeds the threshold current, the switching frequency starts to decrease. This green-mode function dramatically reduces power consumption under light-load and zero-load conditions. Power supplies using the SG6858 can meet even the strictest regulations regarding standby power consumption.
Oscillator Operation
A resistor connected from the RI pin to ground generates a constant current source used to charge an internal capacitor. The charge-time determines the internal clock speed and the switching frequency. Increasing the resistance reduces the amplitude of the input current and the switching frequency. A 95k resistor, RI, results in a 50A constant current, II, and a 70kHz switching (c) System General Corp. Version 1.2.1 (IAO33.0045.B2) -8-
www.sg.com.tw * www.fairchildsemi.com September 25, 2007
Product Specification Low-Cost, Green-Mode PWM Controller for Flyback Converters SG6858
Under-Voltage Lockout (UVLO)
The turn-on and turn-off thresholds of the SG6858 are fixed internally at 16.5V/11.5V. During start-up, the hold-up capacitor must be charged to 16.5V through the start-up resistor to enable SG6858. The hold-up capacitor continues to supply VDD until power can be delivered from the auxiliary winding of the main transformer. VDD must not drop below 11.5V during this start-up process. This UVLO hysteresis window ensures that hold-up capacitor is adequate to supply VDD during start-up.
Built-in Slope Compensation
The sensed voltage across the current sense resistor is used for current-mode control and pulse-by-pulse current limiting. Built-in slope compensation improves stability and prevents sub-harmonic oscillations due to peak-current mode control. The SG6858 has a synchronized, positively-sloped ramp built-in at each switching cycle. The slope of the ramp is:
0.36 x Duty Duty(max .)
(2)
VDD Over-Voltage Protection
VDD over-voltage protection has been built in to prevent damage due to over-voltage conditions. When the voltage VDD exceeds the internal threshold due to abnormal conditions, PWM output is turned off until the VDD voltage drops below the UVLO, then starts up again. Over-voltage conditions are usually caused by open-feedback loops.
Noise Immunity
Noise from the current sense or the control signal can cause significant pulse width jitter, particularly in continuous-conduction mode. While slope compensation helps alleviate these problems, further precautions should still be taken. Good placement and layout practices should be followed. Avoiding long PCB traces and component leads, locating compensation and filter components near the SG6858, and increasing the power MOS gate resistance improves performance.
Gate Output
The BiCMOS output stage is a fast totem pole gate driver. Cross conduction has been avoided to minimize heat dissipation, increase efficiency, and enhance reliability. The output driver is clamped by an internal 17V Zener diode to protect power MOSFET transistors against undesired over-voltage gate signals.
(c) System General Corp. Version 1.2.1 (IAO33.0045.B2)
-9-
www.sg.com.tw * www.fairchildsemi.com September 25, 2007
Product Specification Low-Cost, Green-Mode PWM Controller for Flyback Converters SG6858
REFERENCE CIRCUIT
1 L F1 BD1 CX1 2 4 R1 C1 C2 R5 3 1 N R2 R4 10 9 D1 U1 GND FB RI GATE VDD SENSE 2 8 5 Q1 3 7 3,4 2 GND 2 R10 C7 C8 D5 C9 1 T1 1,2 2 D4 1 1 L2 2 1 L1 2 C3 R3
VO
1 2 3 C6 R9
6 5 4
R7
1
R15 C11
R6
R8 C4
1
D2
2 R11
R13
4
U2 R14 3 2 C10 3 U3 1 R12 2
CY1
BOM
Reference
BD1 CX1 CY1 C1 C2 C3 C4 C6 C7 C8 C9 C10 C11 D1 D2 D4 D5 F1 L1
Component
BD 1A/500V
Reference
L2 Q1 R1,R2 R4,R3 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 T1 U1 U2 U3
(Optional) XC 0.1F (Optional) YC 1000pF/400V (Y1) CC 10nF/500V EC 10F/400V 105 CC 1000pF/500V EC 10F/50V CC 1000pF 0805 (Optional) CC 1000pF/100V 1206 EC 470F/10V 105 EC 220F/10V 105 CC 2200pF 0805 N.C. Diode FRI07 Diode FR102 Diode SB360 (Optional) ZD 6.8V 0.5W R 1/0.5W Inductor 20mH 6x8mm
(Optional) R 10 1206 R 100 1/8W R 33K 0805 R 33K 1/8W R 4.7K 0805 R 0 0805 Transformer EE-16 IC SG6858 IC PC817 IC TL431
(c) System General Corp. Version 1.2.1 (IAO33.0045.B2)
- 10 -
1
Component
Inductor 10H 6mm MOSFET 1A/600V R 750K 1206 R 47K 1206 R 47 1206 R 4.7 1206 R 100 0805 R 10 1206 R 100K 0805
www.sg.com.tw * www.fairchildsemi.com September 25, 2007
Product Specification Low-Cost, Green-Mode PWM Controller for Flyback Converters SG6858
PACKAGE INFORMATION 8 PINS - DIP (D)
D
8 5
X
E1
E
eB
1
4
A1
A2
L b1 b e
Dimensions
Symbol
A A1 A2 b b1 D E E1 e L eB 2.921 8.509 0 6.223 9.017 0.381 3.175 3.302 1.524 0.457 9.271 7.620 6.350 2.540 3.302 9.017 7 3.810 9.525 15 0.115 0.335 0 6.477 0.245 10.160 0.355 3.429
Millimeters Min. Typ.
A
Max.
5.334
Inches Min.
0.015 0.125
Typ.
Max.
0.210
0.130 0.060 0.018 0.365 0.300 0.250 0.100 0.130 0.355 7
0.135
0.400 0.255 0.150 0.375 15
(c) System General Corp. Version 1.2.1 (IAO33.0045.B2)
- 11 -
www.sg.com.tw * www.fairchildsemi.com September 25, 2007
Product Specification Low-Cost, Green-Mode PWM Controller for Flyback Converters SG6858
6 PINS - SOT (T)
D b 6 4 Detail A
E1
E
1 e1
e
3
c
1
R
A2
A
L A1 L1 1 Detail A
Dimensions
Symbol
A A1 A2 b c D E E1 e e1 L L1 L2 R R1 0.10 0.10 0 5 4 10 0.25 8 15 0.30 0.90 0.30 0.08 2.90 2.80 1.60 0.95 1.90 0.45 0.60 0.25 0.004 0.004 0 5 4 10 0.010 8 15 0.60 0.020 1.15
Millimeters Min. Typ.
Max.
1.45 0.15 1.30 0.50 0.22
Inches Min.
Typ.
0.036 0.011 0.003
0.045
0.114 0.110 0.063 0.037 0.075 0.018 0.024 0.010 0.024
1
(c) System General Corp. Version 1.2.1 (IAO33.0045.B2)
- 12 -
www.sg.com.tw * www.fairchildsemi.com September 25, 2007
L2
1 R

Max.
0.057 0.006 0.051 0.020 0.009
Product Specification Low-Cost, Green-Mode PWM Controller for Flyback Converters SG6858
(c) System General Corp. Version 1.2.1 (IAO33.0045.B2)
- 13 -
www.sg.com.tw * www.fairchildsemi.com September 25, 2007

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