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SC656
POWER MANAGEMENT Features

Backlight Driver for 7 LEDs with Charge Pump and PWM Control
Description
The SC656 is a high efficiency charge pump LED driver using Semtech's proprietary charge pump technology. Performance is optimized for use in single-cell Li-ion battery applications. The device provides backlight current using up to seven matched current sinks. The load and supply conditions determine whether the charge pump operates in x, .5x, or 2x mode. The seven backlights can be configured as a single group or split into two independent banks by setting the state of the BANK2 and BANK pins. If only one bank is needed, the BANK2, BANK, ENS and ISETS pins must be grounded. The maximum current per LED in each bank is set by a resistor connected to ISETM or ISETS. LED current can be set between 500A and 25mA. Backlight current is varied by applying a pulse-width modulated (PWM) signal to the ENM pin for the main LED bank and the ENS pin for the sub LED bank. The resulting DC current in each LED (IBL) is equal to the maximum current setting multiplied by the duty cycle of the PWM signal. During PWM operation, a low-pass filter is used to develop a DC current through the LED. The resulting power conversion is more efficient than comparable pulsed current solutions. Backlight fading is initiated when the duty cycle is changed. The 3 x 3 (mm) package and minimal number of small external components make the SC656 an ideal backlight driver solution for space-limited designs.
SC656
Input supply voltage range -- 2.9V to 5.5V Charge pump modes -- x, .5x and 2x PWM dimming control with low pass filter provides DC backlight current (not pulsed) Two independently configurable backlight banks PWM frequency range -- 200Hz to 50kHz Seven adjustable current sinks -- 500A to 25mA Backlight current accuracy .5% typical Backlight current matching 0.5% typical LED float detection Charge pump frequency -- 250kHz Low shutdown current -- 0.A typical Ultra-thin package -- 3 x 3 x 0.6(mm) Fully WEEE and RoHS compliant, and halogen free.
Applications

Cellular phones, smart phones, and PDAs LCD display modules Portable media players Digital cameras Personal navigation devices Display/keypad backlighting and LED indicators
Typical Application Circuit
VBAT = 2.9V to 5.5V CIN 2.2F RISETM RISETS IN GND ISETM ISETS BANK2 BANK1 PWM Signal PWM Signal ENM ENS C1+ C1BL1 BL2 BL3 BL4 BL5 BL6 BL7 C2+ C2OUT
COUT 2.2F
C1 2.2F
C2 2.2F
US Patents: 6,504,422; 6,794,926
September 24, 2009
(c) 2009 Semtech Corporation
SC656
Pin Configuration
ENM OUT C2+ C1+ C1-
Ordering Information
Device
SC656ULTRT()(2) SC656EVB
15 TOP VIEW 14 13 12 T 11
Package
MLPQ-UT-20 3x3 Evaluation Board
20
19
18
17
16
ENS IN ISETM ISETS BL1
1 2 3 4 5
C2GND BANK2 BANK1 BL7
Notes: () Available in tape and reel only. A reel contains 3,000 devices. (2) Lead-free package only. Device is WEEE and RoHS compliant, and halogen free.
6
7
8
9
10
BL2
BL3
BL4
BL5
MLPQ-UT-20; 3x3, 20 LEAD JA = 35C/W
Marking Information
656 yyww xxxx
yyww = Date Code xxxx = Semtech Lot Number
BL6
2
SC656
Absolute Maximum Ratings
IN, OUT (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +6.0 C+, C2+ (V) . . . . . . . . . . . . . . . . . . . . . . . -0.3 to (VOUT + 0.3) Pin Voltage -- All Other Pins (V) . . . . . . . . . -0.3 to (VIN + 0.3) OUT Short Circuit Duration . . . . . . . . . . . . . . . . . Continuous ESD Protection Level() (kV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Recommended Operating Conditions
Ambient Temperature Range (C) . . . . . . . . . . -40 TA +85 Input Voltage (V) . . . . . . . . . . . . . . . . . . . . . . . . . . 2.9 to 5.5 Output Voltage (V) . . . . . . . . . . . . . . . . . . . . . . . . 2.5 to 5.25 Voltage Difference between any two LEDs (V) . . . VF .0 (2)
Thermal Information
Thermal Resistance, Junction to Ambient(3) (C/W) . . . 40 Maximum Junction Temperature (C) . . . . . . . . . . . . . . +50 Storage Temperature Range (C) . . . . . . . . . . . -65 to +50 Peak IR Reflow Temperature (0s to 30s) (C) . . . . . . +260
Exceeding the above specifications may result in permanent damage to the device or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not recommended. NOTES: () Tested according to JEDEC standard JESD22-A4-B. (2) VF(max) = .0V when VIN = 2.9V, higher VIN supports higher VF(max) (3) Calculated from package in still air, mounted to 3 x 4.5(in), 4 layer FR4 PCB per JESD5 standards.
Electrical Characteristics
Unless otherwise noted, TA = +25C for Typ, -40C to +85C for Min and Max, TJ(MAX) = 25C, VIN = 3.7V, CIN= COUT = C= C2= 2.2F, (ESR = 0.03), 500A < IFS_BL < 25mA, Duty Cycle of PWM = 00%, All 7 LEDs connected and enabled as a single bank.
Parameter
Shutdown Current
Symbol
IQ(OFF)
Conditions
TA = 25C x mode, VIN = 3.7V, 7 LEDs at mA on main bank, PWM duty cycle = 5%, RISETM = 4.99k
Min
Typ
0. 2.5 2.8 3.0
Max
2
Units
A
Quiescent Current
IQ
.5x mode, VIN = 3.2V, 7 LEDs at mA on main bank, PWM duty cycle = 5%, RISETM = 4.99k 2x mode, VIN = 2.9V, 7 LEDs at mA on main bank, PWM duty cycle = 5%, RISETM = 4.99k
mA
Maximum Total Output Current Backlight Current Setting Current Gain() Current Set Voltage Backlight Current Matching(2) Backlight Current Accuracy EN/PWM Input Frequency ENM, ENS Minimum High
IOUT(MAX) IFS_BL IGAIN VIN - ISET IBL-BL IBL_ACC fEN/PWM tHIGH_MIN
VIN > 3.0V, sum of all active LED currents, VOUT(MAX) = 4.2V PWM duty cycle = 00%, 200k RISETX 4k Gain from IISETX to IFS_BL Voltage across RISETX IFS_BL = 2mA, Duty = 00% IFS_BL = 2mA, Duty = 00% Duty-cycle percentage changes linearly with IFS_BL
75 0.5 00 -3.5 0.5 .5 0.2 50 +3.5 25
mA mA A/A V % % kHz s
3
SC656
Electrical Characteristics (continued)
Parameter
Current Transition Settling Time ENM/ENS Low Time x Mode to .5x Mode Falling Transition Voltage .5x Mode to 2x Mode Falling Transition Voltage Current Sink Off-State Leakage Current Charge Pump Frequency
Symbol
ts tLT V TRANSx V TRANS.5x IBLn(off ) fPUMP IOUT(SC) VUVLO VUVLO-HYS VOVP TOT TOT-HYS
Conditions
Duty cycle change from 00% to 50%()(4) Time that voltage on ENM or ENS can be low without disabling the device IOUT = 70mA, IBLn = 0mA, VOUT = 3.2V IOUT = 70mA, IBLn = 0mA, VOUT = 4.0V(3) VIN = VBLn = 4.2V VIN = 3.2V OUT pin shorted to GND
Min
Typ
0.5
Max
Units
s
5 3.26 2.90 0. 250 50
ms V V A kHz
Output Short Circuit Current Limit
mA VOUT > 2.5V Increasing VIN -- lockout released 400 2.4 500 OUT pin open circuit, VOUT = VOVP, VIN rising threshold Rising Temperature 5.7 65 25 6.0 V mV V C C
Under Voltage Lockout Threshold UVLO Hysteresis Over-Voltage Protection Over-Temperature OT Hysteresis
Digital Logic Pins -- ENM, ENS, BANK2, AND BANK1 Input High Threshold Input Low Threshold Input High Current Input Low Current VIH VIL IIH IIL VIN = 5.5V VIN = 2.9V VIN = 5.5V VIN = 5.5V .4 0.4 V V A A
Notes: () Guaranteed by design (2) Current matching equals [IBL(MAX) - IBL(MIN] / [IBL(MAX) + IBL(MIN)]. (3) Test voltage is VOUT = 4.0V -- a relatively extreme LED voltage used to force a transition during test. Typically VOUT = 3.2V for white LEDs. (4) The settling time is affected by the magnitude of change in the PWM duty cycle.
4
SC656
Typical Characteristics
VOUT = 3.56V, IOUT = 175mA, 25C
CIN = COUT= C = C2 = 2.2F -- 0603 size (608 metric)
Backlight Accuracy (7 LEDs) -- 25mA Each
8 6 4 2 0 -2 -4 -6 -8 MAX LED MIN LED
8 6 4 2 0 -2 -4 -6 -8
Backlight Matching (7 LEDs) -- 25mA Each
VOUT = 3.56V, IOUT = 175mA, 25C
Backlight Accuracy (%
Backlight Matching (%
4.2
3.9
3.6
VIN (V
3.3
3
2.7
4.2
3.9
3.6
VIN (V
3.3
3
2.7
Backlight Accuracy (7 LEDs) -- 12mA Each
8 6
Backlight Accuracy (%
Backlight Matching (7 LEDs) -- 12mA Each
8 6 4 2 0 -2 -4 -6 -8 VOUT = 3.42V, IOUT = 84mA, 25C
VOUT = 3.42V, IOUT = 84mA, 25C
2 0 -2 -4 -6 -8
MAX LED MIN LED
Backlight Matching (%
4
4.2
3.9
3.6
VIN (V
3.3
3
2.7
4.2
3.9
3.6
VIN (V
3.3
3
2.7
Backlight Accuracy (7 LEDs) -- 5mA Each
8 6
Backlight Accuracy (%
Backlight Matching (7 LEDs) -- 5mA Each
8 6 4 2 0 -2 -4 -6 VOUT = 3.28V, IOUT = 35mA, 25C
VOUT = 3.28V, IOUT = 35mA, 25C
2 0 -2 -4 -6 -8
MAX LED
MIN LED
Backlight Matching (%
3.3 3 2.7
4
4.2
3.9
3.6
-8
VIN (V
4.2
3.9
3.6
VIN (V
3.3
3
2.7
5
SC656
Typical Characteristics (continued)
Charge Pump Efficiency (7 LEDs) -- 25mA Each
100 VOUT = 3.56V, IOUT = 175mA, 25C
Backlight Current (7 LEDs) -- 25mA Each
400 350
Battery Current (mA
VOUT = 3.56V, IOUT = 175mA, 25C
90
300 250 200
Efficiency (%
80
70
60
150 100
50
4.2
3.9
3.6
VIN (V
3.3
3
2.7
4.2
3.9
3.6
VIN (V
3.3
3
2.7
Charge Pump Efficiency (7 LEDs) -- 12mA Each
100 VOUT = 3.42V, IOUT = 84mA, 25C
Backlight Current (7 LEDs) -- 12mA Each
135 VOUT = 3.42V, IOUT = 84mA, 25C
90
125
80
70
Battery Current (mA
115
Efficiency (%
105
95 85 75
60
50
4.2
3.9
3.6
VIN (V
3.3
3
2.7
4.2
3.9
3.6
VIN (V
3.3
3
2.7
Charge Pump Efficiency (7 LEDs) -- 5mA Each
100 VOUT = 3.28V, IOUT = 35mA, 25C
Backlight Current (7 LEDs) -- 5mA Each
80 70 VOUT = 3.28V, IOUT = 35mA, 25C
90
Battery Current (mA
4.2 3.9 3.6 3.3 3 2.7
Efficiency (%
60
80
50
70
40 30 20
60
50
VIN (V
4.2
3.9
3.6
VIN (V
3.3
3
2.7
6
SC656
PWM Accuracy -- 4.2V PWM Accuracy -- 4.2V
Typical Characteristics (continued)
PWM Accuracy -- 4.2V
20 VIN = 4.2V, RISET = 4.99k, Calculated IBL = (100/RISET) x Duty Cycle
Percentage of Maximum IBL -- 4.2V
100 VIN = 4.2V, RISET = 4.99k
12
Percentage of Maximum IBL (%
16
80
Calculate IBL (mA
60
8
50kHz
40
50kHz
4
32kHz 200Hz
20
32kHz
200Hz
0
0
4
8 12 Meaure IBL (mA
PWM Accuracy -- 4.2V
16 20
0
0
20
40 60 PWM Duty Cycle (%
PWM Accuracy -- 4.2V
80 100
PWM Accuracy -- 3.7V
20 VIN = 3.7V, RISET = 4.99k, Calculated IBL = (100/RISET) x Duty Cycle
100
Percentage of Maximum IBL -- 3.7V
VIN = 3.7V, RISET = 4.99k
Percentage of Maximum IBL (%
16
Calculate IBL (mA
80
12
60
8
50kHz
40
50kHz
4
32kHz
200Hz
20
32kHz
200Hz
0
0
4
8 12 Meaure IBL (mA
16 20 PWM Accuracy -- 4.2V
0
0
20
40 60 PWM Duty Cycle (%
PWM Accuracy -- 4.2V 100 80
PWM Accuracy -- 2.9V
20 VIN = 2.9V, RISET = 4.99k, Calculated IBL = (100/RISET) x Duty Cycle
100
Percentage of Maximum IBL -- 2.9V
VIN = 2.9V, RISET = 4.99k
12
Percentage of Maximum IBL (%
16
80
Calculate IBL (mA
60
50kHz
8
32kHz
40
4
50kHz 200Hz
20
32kHz
200Hz
0
0
4
8 12 Meaure IBL (mA
16
20
0
0
20
40
60
80
100
PWM Duty Cycle (%
7
SC656
Typical Characteristics (continued)
Ripple -- 1X Mode
VIN=4.2V, RISET = 4k, 7 Backlights -- 25 mA each, 25C
Ripple -- 1X Mode
VIN=4.2V, RISET = 5.56k, 7 Backlights -- 8 mA each, 25C
VIN (00mV/div)
VIN (00mV/div)
VOUT (00mV/div)
VOUT (00mV/div)
Time (10i i i
Time (10i i i
Ripple -- 1.5X Mode
VIN=3.2V, RISET = 4k, 7 Backlights -- 25 mA each, 25C
Ripple -- 1.5X Mode
VIN=3.2V, RISET = 5.56k, 7 Backlights -- 8 mA each, 25C
VIN (00mV/div)
VIN (00mV/div)
VOUT (00mV/div)
VOUT (00mV/div)
Time (10i i i
Time (10i i i
Ripple -- 2X Mode
VIN=2.9V, RISET = 4k, 7 Backlights -- 25 mA each, 25C
Ripple -- 2X Mode
VIN=2.9V, RISET = 5.56k, 7 Backlights -- 8 mA each, 25C
VIN (00mV/div)
VIN (00mV/div)
VOUT (00mV/div)
VOUT (00mV/div)
Time (10i i i
Time (10i i i
8
SC656
Typical Characteristics (continued)
Start-up -- 0% to 50%
VIN = 3.7V, 0 to 50% duty cycle, RISET = 4.99k, fPWM = 32kHz
Start-up -- 0% to 100%
VIN = 3.7V, 0 to 00% duty cycle, RISET = 4.99k, no PWM 20mA
0mA IBL (0.0mA/div) 0mA-- IBL (0.0mA/div) 0mA--
VPWM (2V/div) 0V-- 50% Time (200mi i i
VPWM (2V/div) 0V-- 00% Time (200mi i i
IBL Settling Time -- 50% to 100%
VIN = 3.7V, RISET = 4.99k, fPWM = 32kHz 20mA IBL (0.0mA/div) 0mA-- 0mA IBL (0.0mA/div) 0mA--
IBL Settling Time -- 100% to 50%
VIN = 3.7V, RISET = 4.99k, fPWM = 32kHz 20mA 0mA
VPWM (2V/div) 0V-- 50% 00% Time (200mi
VPWM (2V/div) 0V-- 00% 50% Time (200mi i i
DC Backlight Current -- 32kHz PWM
VIN = 3.7V, 50% duty cycle, RISET = 4.99k, IBL = 0mA
DC Backlight Current -- 200Hz PWM
VIN = 3.7V, 50% duty cycle, RISET = 4.99k, IBL = 0mA
IBL (0.0mA/div) 0mA--
IBL (0.0mA/div) 0mA--
VPWM (2V/div) 0V-- Time (20i i i
VPWM (2V/div) 0V-- Time (1mi i i
9
SC656
Pin Descriptions
Pin #
2 3 4 5 6 7 8 9 0 2 3 4 5 6 7 8 9 20
Pin Name
ENS IN ISETM ISETS BL BL2 BL3 BL4 BL5 BL6 BL7 BANK BANK 2 GND C2CC+ C2+ OUT ENM
Pin Function
Enable pin for sub display LED bank -- also used as the PWM dimming control input for this bank Battery voltage input Current setting pin -- connect a resistor between ISETM and IN to set the main bank LED current. Current setting pin -- connect a resistor between ISETS and IN to set the sub bank LED current. Current sink output for backlight LED -- leave this pin open if unused Current sink output for backlight LED 2 -- leave this pin open if unused Current sink output for main backlight LED 3 -- leave this pin open if unused Current sink output for main backlight LED 4 -- leave this pin open if unused Current sink output for main backlight LED 5 -- leave this pin open if unused Current sink output for main backlight LED 6 -- leave this pin open if unused Current sink output for main backlight LED 7 -- leave this pin open if unused Logic input that, along with BANK 2, controls the configuration of the main and sub bank functions. See application information section for details. Logic input that, along with BANK , controls the configuration of the main and sub bank functions. See application information section for details. Ground pin Negative connection to bucket capacitor 2 Negative connection to bucket capacitor Positive connection to bucket capacitor Positive connection to bucket capacitor 2 Charge pump output -- all LED anode pins are connected to this pin. Enable pin for the main display LED bank -- also used as the PWM dimming control input for this bank
0
SC656
Block Diagram
C1+ C1- C2+ C217
VIN
16
18
15
VOUT
IN GND
2
Fractional Charge Pump (1x, 1.5x, 2x)
19
OUT
14
Oscillator Control Interface, Level Converter, Digital LPF Current Setting Block Current Setting Block Control Interface, Level Converter, Digital LPF LED Bank Configuration Logic
ENM
20
5 6 7 8 9 10 11
BL1 BL2 BL3 BL4 BL5 BL6 BL7
ISETM
3
ISETS
4
ENS
1
BANK2 BANK1
13 12
SC656
Applications Information
General Description
This design is optimized for handheld applications supplied from a single Li-Ion cell and includes the following key features: IOUT up to 90mA. For output currents higher than 90mA, a nominal value of 2.2F is recommended for COUT and CIN. Capacitors with X7R or X5R ceramic dielectric are strongly recommended for their low ESR and superior temperature and voltage characteristics. Y5V capacitors should not be used as their temperature coefficients make them unsuitable for this application. Capacitor Recommendations The full rated output of 75mA is achieved using 2.2F 0603 size capacitors for input, output, and bucket capacitors. For applications which do not require the full 75mA output capability of the SC656 , a lower cost and smaller size capacitor option may be used. The F capacitor in Table may be used with no loss in accuracy, for up to 90mA of output current. Table 1 -- Capacitor Recommendations
Capacitance Value of CIN = COUT = C1 = C2
2.2F .0F
* * *
A high efficiency fractional charge pump that supplies power to all LEDs Seven matched current sinks that control LED backlighting current, providing 500A to 25mA per LED Two LED bank options with independent current settings and enable pins with PWM control of LED brightness.
High Current Fractional Charge Pump The backlight outputs are supported by a high efficiency, high current fractional charge pump output at the OUT pin. The charge pump multiplies the input voltage by , .5, or 2 times. The charge pump switches at a fixed frequency of 250kHz in .5x and 2x modes and is disabled in x mode to save power and improve efficiency. The mode selection circuit automatically selects the x, .5x, or 2x mode based on circuit conditions such as LED voltage, input voltage, and load current. The x mode is the most efficient mode, followed by .5x and 2x modes. Circuit conditions such as low input voltage, high output current, or high LED voltage place a higher demand on the charge pump output. A higher numerical mode (.5x or 2x) may be needed momentarily to maintain regulation at the OUT pin during intervals of high demand. The charge pump responds to momentary high demands, setting the charge pump to the optimum mode to deliver the output voltage and load current while optimizing efficiency. Hysteresis is provided to prevent mode toggling. The charge pump requires two bucket capacitors for proper operation. One capacitor must be connected between the C+ and C- pins and the other must be connected between the C2+ and C2- pins as shown in the Typical Application Circuit diagram. These capacitors should be equal in value, with a minimum capacitance of F to support the charge pump current requirements. The device also requires at least F capacitance on the IN pin and at least F capacitance on the OUT pin to minimize noise and support the output drive requirements of
Size Code EIA (JIS)
0603 (608) 0402 (005)
Application IOUT Limit
up to IOUT = 75mA() up to IOUT = 90mA(2)(3)
Notes: () Note that 2.2F in the 0402 size is not equivalent to 2.2F in the 0603 size, so 0402 may not be substituted for this application. (2) Larger size capacitors may be substituted. (3) Exceeding 90mA, or using less than .0F, may cause excessive peak-to-peak output ripple, (>20mV), and some loss of accuracy in .5x mode.
Bank Control Options The backlight drivers can be configured as a single bank or as two independently controlled banks. The configuration of the banks is determined by the BANK2 and BANK pins as described in Table 2. The ENM and ISETM pins control the brightness of LEDs assigned to the main bank, and the ENS and ISETS pins allow the sub bank current to be set independently as described in the following section. Note that when both BANK2 and BANK are set to 0, the sub bank feature is disabled. In this case, both ENS and ISETS should be tied to GND.
2
SC656
Applications Information (continued)
Table 2 -- Backlight Bank Configuration Settings
Bank 2
0 0
Bank 1
0 0
Main Bank
BL -- BL7 BL2 -- BL7 BL3 -- BL7 BL4 -- BL7
Sub Bank
none BL BL -- BL2 BL -- BL3
Minimum Duty Cycle (%
LED Backlight Current Sinks The full scale backlight current (IFS_BL) is set via the current through the ISET pin controlling the corresponding LED bank (ISETM or ISETS) . The IFS_BL is regulated to the value of the ISETM or ISETS pin current multiplied by an internal gain of 00A/A. RISETM and RISETS are used to control the current into the ISETM and ISETS pins. The relationship between each resistance RISETx and the full scale backlight current is: RISETx = 00/IFS_BL All backlight current sinks have matched currents, even when there is a variation in the forward voltages (VF ) of the LEDs. A VF of .0V is supported when the input voltage is at 2.9V. Higher VF LED mis-match is supported when VIN is higher than 2.9V. All current sink outputs are compared and the lowest output is used for setting the voltage regulation at the OUT pin. This is done to ensure that sufficient bias exists for all LEDs. Any unused LED driver outputs must be left open for normal operation. PWM Operation A PWM signal on the ENM or ENS pin can be used to adjust the DC current through the LEDs. When the duty cycle is 00%, the backlight current through each LED (IBL) equals the full scale current set by the corresponding ISET pin. As the duty cycle decreases, the ENM or ENS input samples the control signal and converts the duty cycle to a DC current level. In conventional PWM controlled systems, the output current pulses on and off with the PWM input to achieve an average output current. Providing a DC current through the LEDs instead of a pulsed current provides an efficiency advantage over other PWM controlled systems by allowing the charge pump to remain in x mode longer since the maximum current is equal to the average current.
PWM Sampling The sampling system that translates the PWM signal to a DC current requires the ENM and ENS pins to have a minimum high time tHIGH_MIN to set the DC level. High time less than tHIGH_MIN impacts the accuracy of the target I BL. The minimum duty cycle needed to support the minimum high time specification varies with the applied PWM frequency (see figure ). Note that use of a lower PWM frequency, from 200Hz to 0kHz, will support lower minimum duty cycle and an extended backlight dimming range.
5 tHIGH_MIN = 1s
4
3
2
1
0
0.2
10
20
30
40
50
PWM Frequency (kHz
Figure 1 -- Minimum Duty Cycle Shutdown Mode Shutdown occurs after ENM and ENS are both held low for an interval of 5ms or more. When the ENM and ENS pins are both held low for 5ms or less, the device will not shutdown.
Protection Features
The SC656 provides several protection features to safeguard the device from catastrophic failures. These features include:
* * * *
Output Open Circuit Protection Over-Temperature Protection Charge Pump Output Current Limit LED Float Detection
3
SC656
Applications Information (continued)
Output Open Circuit Protection Over-Voltage Protection (OVP) at the OUT pin prevents the charge pump from producing an excessively high output voltage. In the event of an open circuit between the OUT pin and all current sinks (no loads connected), the charge pump runs in open loop and the voltage rises up to the OVP limit. OVP operation is hysteretic, meaning the charge pump will momentarily turn off until VOUT is sufficiently reduced. The maximum OVP threshold is 6.0V, allowing the use of a ceramic output capacitor rated at 6.3V. Over-Temperature Protection The Over-Temperature (OT) protection circuit prevents the device from overheating and experiencing a catastrophic failure. When the junction temperature exceeds 65C, the device goes into thermal shutdown with all outputs disabled until the junction temperature is reduced. All register information is retained during thermal shutdown. Hysteresis of 20C is provided to ensure that the device cools sufficiently before re-enabling. Charge Pump Output Current Limit The device limits the charge pump current at the OUT pin. If the OUT pin is shorted to ground, or VOUT is lower than 2.5V, the typical output current limit is 70mA. The output current is limited to 225mA when over loaded resistively with VOUT greater than 2.5. LED Float Detection Float detect is a fault detection feature of the LED backlight outputs. If an output is programmed to be enabled and an open circuit fault occurs at any backlight output, that output will be disabled to prevent a sustained output OVP condition from occurring due to the resulting open loop. Float detect ensures device protection but does not ensure optimum performance.
PCB Layout Considerations
The layout diagram in Figure 2 illustrates a proper two layer PCB layout for the SC656 and supporting components. Following fundamental layout rules is critical for achieving the performance specified in the Electrical Characteristics table. The following guidelines are recommended when developing a PCB layout:
OUT Ground Plane
GND
COUT
C1 C2
ENM
OUT
C2+
C1+
CIN
IN
RSETM
ENS IN ISETM ISETS RSETS BL1
C1-
GND SC656
C2GND BANK2 BANK1 BL7
GND
BL4
BL2
BL3
Figure 2 -- Recommended Layout
4
BL5
BL6
SC656
Applications Information (continued)
* *
* * *
Place all bucket and decoupling capacitors -- C, C2, CIN, and COUT -- as close to the device as possible. All charge pump current passes through pins IN, OUT, C+, C2+, C-, and C2-. Therefore, ensure that all connections to these pins make use of wide traces so that the voltage drop on each connection is minimized. The GND pin should be connected to a ground plane using multiple vias to ensure proper thermal connection for optimal heat transfer. Make solid ground connections between the grounds of the COUT, CIN, and the GND pin on the device. Resistors RSETM and RSETS should be connected as shown in Figure 2, close to pins IN and ISET. The placement and routing shown minimizes parasitic capacitance at the ISET pin.
* *
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Figure 3 shows the pads on layer that should be connected with vias to layer 2. CIN, COUT and the GND pin all use vias to connect to the ground plane. Figure 4 shows layer 2, which functions as the ground plane. Layer 2 is also used for routing signals to pins ENM, ENS, BANK, and BANK2. A void in the copper beneath the ISETM and ISETS pins serves to reduce capacitance coupled from these pins to ground. Avoid coupling noise to the ENM and ENS pins. This will help prevent unintended clocking of the PWM. The layout should be routed to achieve the least possible trace to trace capacitance between ENM and ENS. Also, minimize trace capacitance between ENM or ENS and any high speed signals.
Figure 3 -- Layer 1
Figure 4 -- Layer 2
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SC656
Outline Drawing -- MLPQ-UT-20 3x3
A D B DIM A A1 A2 b D D1 E E1 e L N aaa bbb DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX .020 .024 0.50 0.60 .000 .002 0.00 0.05 (.006) (0.152) .006 .008 .010 0.15 0.20 0.25 .114 .118 .122 2.90 3.00 3.10 .061 .067 .071 1.55 1.70 1.80 .114 .118 .122 2.90 3.00 3.10 .061 .067 .071 1.55 1.70 1.80 .016 BSC 0.40 BSC .012 .016 .020 0.30 0.40 0.50 20 20 .003 0.08 .004 0.10
PIN 1 INDICATOR (LASER MARK)
E
A2 A aaa C A1 e LxN E/2 E1 2 1 N D/2 bxN bbb NOTES: 1. 2. 3. CAB D1 C SEATING PLANE
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS. DAP IS 1.90 x 1.90mm.
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SC656
Land Pattern -- MLPQ-UT-20 3x3
K R DIM (C) Z C G H K P R X Y Z (.114) .083 .067 .067 .016 .004 .008 .031 .146 DIMENSIONS INCHES MILLIMETERS (2.90) 2.10 1.70 1.70 0.40 0.10 0.20 0.80 3.70
H
G
Y X
P
NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. THERMAL VIAS IN THE LAND PATTERN OF THE EXPOSED PAD SHALL BE CONNECTED TO A SYSTEM GROUND PLANE. FAILURE TO DO SO MAY COMPROMISE THE THERMAL AND/OR FUNCTIONAL PERFORMANCE OF THE DEVICE.
3.
Contact Information
Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 9302 Phone: (805) 498-2 Fax: (805) 498-3804 www.semtech.com
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