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A8435
High Efficiency Charge Pump White LED Driver
Features and Benefits
Proprietary adaptive control scheme (1x, 1.5x) Maximum efficiency, over 92% 0.5% LED current matching 1 MHz operating frequency Flexible dimming control: Serial 11-level dimming, down to 5% PWM 2-bit parallel Drives up to 4 white LEDs 30 mA per LED 120 mA total continuous output Low input ripple and EMI Soft-start limits inrush current Short circuit protection Overvoltage protection Thermal shutdown protection Space-saving MLP-16 package: 3 x 3 mm footprint Very thin 0.75 mm nominal height package
Description
The A8435 high efficiency charge pump IC offers a simple, low-cost white LED driver solution for portable electronics display applications. Using a proprietary control scheme (1x, 1.5x), the A8435 can output well-matched currents for up to 4 LEDs, while maintaining the highest efficiency over most of the Li-ion battery lifetime. The A8435 accepts an input range of 2.7 to 5.5 V and delivers up to 30 mA for each of the four regulated current sources. The A8435 can deliver a total continuous output current of 120 mA, meeting the requirements of most Li-ion battery-powered white LED backlight applications. Outputs can also be tied together for WLED flash/torch applications. The A8435 offers flexible options for LED current driving. The LED current can be set by any of the following methods: (a) choosing an appropriate value for RSET, (b) 2-bit parallel control with 3 levels, (c) PWM control, or (d) serial programming The A8435 is available in a very thin profile 0.75 mm (nominal height) 3 x 3 mm QFN/MLP-16 package (ES), fitting the needs of space-conscious applications. Applications include: White LED backlights for cellular phones, PDAs Digital cameras, camcorders Portable audio devices Other portable device white LED backlighting 120 mA WLED flash/torch

Package: 16 pin QFN/MLP (suffix ES)
Approximate Scale
Typical Applications
VBATT 2.7 to 5.5 V
VIN VOUT
VBATT 2.7 to 5.5 V
VIN VOUT
C1+ LED1 C1-
CIN 1 F
C1 1 F C2 1 F
COUT 1 F
CIN 1 F
C1 1 F C2 1 F
C1+ LED1 C1-
COUT 1 F
C2+
A8435
LED2
C2+
A8435
LED2
C2- EN1 EN2 NC CTRL On/Off and Dimming Control GND
LED3
C2-
LED3
Single-Wire On/Off and Dimming Control
LED4 ISET
EN1 EN2 CTRL GND LED4 ISET
RSET
RSET
Figure 1. Typical Circuit. Dual wire control configuration: 2-bit parallel or PWM dimming.
Figure 2. Typical Circuit. Single wire control configuration.
A8435-DS, Rev. 1
A8435
Selection Guide
Part Number A8435EESTR-T
High Efficiency Charge Pump White LED Driver
Packaging* 7-in. reel, 1500 pieces/reel Package Type ES, 3 x 3 mm QFN/MLP-16
*Contact Allegro for additional packing options.
Functional Block Diagram
C1 1 F C1+ C1 - C2+ C2 1 F C2-
VIN Fractional Charge Pump (1x and 1.5x) CIN 1 F
+ -
VOUT
COUT 1 F
EN1 EN2 CTRL Minimum Select Control, Clock, and Reference LED1 LED2 LED3 Current Mirror LED4
+ -
ISET
+ - + - + - + -
RSET
GND
Absolute Maximum Ratings
Input or Output Voltage VIN, VOUT, C1+, C1-, C2+, and C2- pins...................... -0.3 to 6 V All other pins..................................................... -0.3 to VIN + 0.3 V VOUT Short Circuit to GND ....................................................Continuous Operating Ambient Temperature, TA ..................................... -40C to 85C Maximum Junction Temperature, TJ(max) ............................................. 150C Storage Temperature, TS ................................................... -55C to 150C
Package Thermal Characteristics RJA = 68 C/W, on a 4-layer board (vendor data; unverified) Additional information is available on the Allegro Web site.
Package is lead (Pb) free, with 100% matte tin leadframe plating.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A8435
High Efficiency Charge Pump White LED Driver
Pin-out Diagram
16 C1+
15 C2-
C2+ VOUT EN1 CTRL
1 2 3 4 5 6 7 8 EP
13 C1- 12 NC 11 GND 10 LED3 9 LED4 LED1
ISET
EN2
(Top View)
Terminal List Table
Name C1- C1+ C2- C2+ CTRL EN1 EN2 EP GND ISET LED1 LED2 LED3 LED4 NC VIN VOUT Pin Number 13 16 15 1 4 3 5 - 11 6 8 7 10 9 12 14 2 Negative terminal of capacitor C1. Positive terminal of capacitor C1. Negative terminal of capacitor C2. Positive terminal of capacitor C2. Brightness control scheme toggle. For 2-bit parallel or PWM dimming, leave open or tie to VIN (see table 1). For single-wire serial input dimming, connect to GND (see figure 2). When CTRL is open or HIGH: Enable and dimming control input 1 (see table 1). When CTRL is grounded: single-wire enable and dimming control (see table 1 and figure 2). (Do not leave unconnected.) When CTRL is open or HIGH: Enable and dimming control input 2 (see table 1). When CTRL is grounded: this pin disables shutdown. (Do not leave unconnected.) Exposed metal pad on bottom side. Connect this to ground plane for better thermal performance. Ground. Connect RSET resistor to ground to set desired constant current through LEDs. Current sink for LED1. Connect to VIN or VOUT if not used for LED. (Do not leave unconnected.) Current sink for LED2. Connect to VIN or VOUT if not used for LED. (Do not leave unconnected.) Current sink for LED3. Always connect this pin to LED. Current sink for LED4. Connect to VIN or VOUT if not used for LED. (Do not leave unconnected.) No Connection. Power supply voltage input. Charge pump voltage source output for connection to the LED anodes. Function*
* See Application Information section for cited figure and tables.
LED2
14 VIN
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A8435
High Efficiency Charge Pump White LED Driver
ELECTRICAL CHARACTERISTICS1 VIN = VEN1 = VEN2 = 3.6 V, C1 = C2 = 1 F, TA = -40 to 85C, typical values at TA = 25C (unless otherwise noted) Characteristics Symbol Test Conditions Min. Typ. Max.
Input Voltage Range Undervoltage Lockout Threshold UVLO Hysteresis Window Quiescent Current Soft-Start Completion Time ISET Bias Voltage ISET Leakage in Shutdown ISET Current Range VIN VUVLO VUVLOHYS IQ tSS VISETBIAS VISETLKG IISET IISET = 60 A, EN1 = VIN, EN2 = GND CTRL = open or HIGH EN1 = GND, EN2 = VIN IISET = 60 A, CTRL = LOW ILED Accuracy LED Current Matching2 Regulation Voltage at LEDx (1.5x) Open Loop Output Resistance3 1x to 1.5x Mode Transition Voltage at LEDx Transition to Dropout Voltage Difference4 LED Leakage in Shutdown Oscillator Frequency Output Overvoltage Protection5 EILED ILED VLED ROUT VTrans Vdr VLEDLKG fosc VOVP VIH VIL IIH IIL tLO tHI Time7 tHI(Init) tSHDN TSHDN First EN1 pulse after shutdown Falling edge of EN1 pulse 20C hysteresis VIH = VIN VIL = GND Open circuit at any LED that is programmed to be in the ON state Full brightness EN1 = EN2 = VIN Switching, TA = 25C EN1 = EN2 = GND, TA = 25C VIN falling, VUVLOHYS = 35 mV 2.7 2.25 - - - - 0.56 - 40 190 105 51 - - - - - - - - - - - 1.6 - - - 0.5 0.5 100 - - - 2.45 35 2.8 0.1 2 0.6 0.01 - 219 121 60 200 0.9 0.5 150 1.1 3.6 100 60 0.01 1 5.74 - - - - - - - 2 165 5.5 2.60 - 4 1 - 0.64 1 140 245 137 69 - - - - - - - - 1 - - - 0.4 1 1 500 - - 3 -
Units
V V mV mA A ms V A A A/A A/A A/A A/A % % mV mV mV A MHz V V V A A s s s ms C
ISET to LEDx Current Ratio
ILEDx / IISET
EN1 = EN2 = VIN, RSET = 4.3 k VIN =3.6 V, ILED = 30 mA per LED EN1 = EN2 = VIN 1x mode: [(VIN - VOUT) / IOUT] 1.5x mode: [(1.5 x VIN - VOUT) / IOUT] VLEDx Falling Measured as VTrans - VDropout EN1 = EN2 = GND, VIN = 5.5 V, TA = 25C
CTRL, EN1, EN2 Input High Logic Threshold6 CTRL, EN1, EN2 Input Low Logic Threshold6 Input High Current Input Low Current EN1 Pulse Low Time7 EN1 Pulse High Time7 Initial EN1 Pulse High Shutdown Delay7 Thermal-Shutdown Threshold
1Specifications
guaranteed by design over operating temperature range, -40C to 85C. 2LED current matching is defined as (I LEDX - ILED(AVG)) / ILED(AVG) . 3The Open Loop Output Resistance for 1.5x mode is measured with one of the LEDx pins tied to ground or open (thus its voltage is always less than 80 mV). 4Dropout Voltage, V Dropout, is defined as the LEDx-to-GND voltage at which ILEDx drops 10% below the value of ILEDX at VLEDX = 200 mV. 5Guaranteed by design. 6EN2 is not used when CTRL is tied to ground. 7Applies only when CTRL is tied to ground. See figure 3 in Application Information section.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A8435
High Efficiency Charge Pump White LED Driver
Tests performed using application circuit shown in figure 1: dual wire control; and VIN = 3.6 V, EN1 = EN2 = VIN, CIN = C1 = C2 = COUT = 1 F, RSET = 7.5 k, TA = 25C (unless otherwise noted)
Performance Characteristics
Efficiency versus Supply Voltage
Over Range of Dimming Levels, VIN Falling
100
90
80
(%)
Dimming Level (mA) 4.75
9.8 17.6 (Full Brightness)
70
60
50 2.70
2.90
3.10
3.30
3.50 VIN (V)
3.70
3.90
4.10
Supply Current versus Supply Voltage
Over Range of Dimming Levels (mA)
120
100
VIN Falling
80
VIN Rising 17.6 mA
IBATT (mA)
60
VIN Falling
40
VIN Rising
9.8 mA
VIN Rising
20
4.75 mA
VIN Falling
0 2.70
2.90
3.10
3.30
3.50
3.70
3.90
4.10
VIN (V)
LED Current versus Supply Voltage
Matching Between LEDs <1% Over Range of VIN
20 19 18 17
ILED (mA)
16 15 14 13 12 11 10 2.0 2.5 3.0 3.5
VIN (V)
4.0
4.5
5.0
5.5
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A8435
Startup Response
High Efficiency Charge Pump White LED Driver
VEN
Symbol C1 C2 C3 t
Parameter VEN IBATT VOUT time
Units/Division 5V 50 mA 2V 500 s
C1
IBATT C2
C3
VOUT
t
2-Bit (EN1-EN2) Dimming Response
Symbol C1 C2 t Conditions EN2 = VIN
Parameter VEN1 IOUT time
Units/Division 2V 50 mA 5 s
VEN C1
IOUT C2
t
11-Level Single-Wire Serial Dimming Response
Symbol Parameter Units/Division C1 VEN1 2V C2 IOUT 50 mA C3 VOUT 2V t time 10 ms Conditions EN2 = CTRL = GND, apply control signal to EN1
C1
VEN1
IOUT C2
VOUT C3 t
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A8435
High Efficiency Charge Pump White LED Driver
Application Information
Setting LED Current The LED current level, ILEDX, is set by the value chosen for the external resistor, RSET, which is connected to the ISET terminal. The full current (100%) level for ILEDX can be calculated using the following formulas:
Setting
CTRL = Open or HIGH CTRL = LOW
Dimming The A8435 offers serial, 2-bit parallel, and PWM dimming control. When the CTRL pin is pulled LOW, the EN1 pin accepts one-wire serial pulse input both to enable the part, and to select one of the 11 dimming levels, from 100% down to 5% (see table 1). With EN2 low, when EN1 is pulled high, the IC turns on. The initial LED current defaults to 100% after softstart is complete. The tLO must be < 500 ms to avoid shutdown. With EN2 high, the operation of EN1 is the same as when EN2 is low, except shutdown is disabled (TLO = ).
Formula
RSET () = 0.6 V x 219 / ILEDX RSET () = 0.6 V x 200 / ILEDX
Table 1. CTRL, EN1, and EN2 Pin States CTRL Open or HIGH Open or HIGH Open or HIGH Open or HIGH LOW EN1 LOW EN2 Brightness LED Current, ILED 0 60 x IISET 121 x IISET 219 x IISET LOW Shutdown
LOW HIGH 27% Brightness HIGH LOW 55% Brightness HIGH HIGH Full Brightness
Adjustable; 11 levels of dimming from Pulse No 100% to 5% (see figure 3; 100% corinput effect responds to 200 x IISET) LOW LOW Shutdown > 2 ms
LOW
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A8435
High Efficiency Charge Pump White LED Driver
When changing from one specific brightness level to another, the user may not want to keep the existing brightness level stored in memory. A simpler method is to program a shutdown and re-enable, followed by an appropriate number of pulses (from 100%) to reach the target brightness level. The total "LED off" time during shutdown, re-enable, and brightness programming can be kept sufficiently short such that no delay is discernable to the eye. Shutdown If the CTRL pin is unconnected or HIGH, the device enters the shutdown mode when EN1 and EN2 are pulled LOW. When configured to have a serial pulse dimming control (the CTRL pin is grounded), the EN1 and the EN2 pins must be pulled LOW for longer than tSHDN (2 ms typical) in order to enter shutdown mode.
The output is high impedance after shutdown. Disabling Unused LEDs If any WLED is not used, connect the corresponding pin to either VIN or VOUT to disable it. Never leave open any unused WLED pin. LED pins will sink 30 A typical when connected to VIN or VOUT and the IC is enabled. LED3 must always be selected. For example, to drive 2 LEDs, select LED3 and one of either LED1, LED2, or LED4. Component Selection Ceramic capacitors with X5R or X7R dielectric are recommended for the input capacitor, CIN, the output capacitor, COUT, and the charge pump capacitors, C1 and C2.
0
tHI(Init)
1
2
3
4
5
6
7
8
9
10
11
EN1
tSS 100% 90% 80% 70%
t LO
t HI 100% 90%
tSHDN
60%
50%
40%
IILEDX SHDN
30% 20%
10%
5%
SHDN
Figure 3. Single-Wire Serial Dimming Control, at pin EN1; CTRL = LOW, EN2 = LOW.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A8435
High Efficiency Charge Pump White LED Driver
Package ES, 3 x 3 mm 16-Pin QFN/MLP
3.15 .124 2.85 .112 16 Preliminary dimensions, for reference only (reference JEDEC MO-220WEED-4) Dimensions in millimeters U.S. Customary dimensions (in.) in brackets, for reference only Dimensions exclusive of mold flash, gate burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown A Terminal #1 mark area B Exposed thermal pad (reference only, terminal #1 identifier appearance at supplier discretion) C Reference land pattern layout (reference IPC7351 QFN50P300X300X80-17W4M); adjust as necessary to meet application process requirements and PCB layout tolerances; when mounting on a multilayer PCB, thermal vias at the exposed thermal pad land can improve thermal dissipation (reference EIA/JEDEC Standard JESD51-5) 16X 0.08 [.003] C 16X 0.30 .012 0.18 .007 0.10 [.004] M C A B 0.05 [.002] M C 0.50 .020 0.30 .012 NOM 0.90 .035 NOM C 1 12X 0.20 .008 MIN 1.70 .067 NOM 0.50 .020 0.30 .012 3.10 .122 NOM 2 1 B 16 0.50 .020 NOM 1.70 .067 NOM 1 2
A B
A 3.15 .124 2.85 .112
SEATING PLANE 0.80 .031 0.70 .028 0.20 .008 REF 0.05 .002 0.00 .000
C
1.70 NOM
.067
4X 0.20 .008 MIN 1.70 .067 NOM 3.10 .122 NOM
16 16X 0.20 .008 MIN 0.23 x 0.23 .009 x .009 REF
The products described here are manufactured under one or more U.S. patents or U.S. patents pending. Allegro MicroSystems, Inc. reserves the right to make, from time to time, such departures from the detailed specifications as may be required to permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the information being relied upon is current. Allegro products are not authorized for use as critical components in life-support devices or systems without express written approval. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement of patents or other rights of third parties which may result from its use. Copyright(c)2005, 2006 AllegroMicroSystems, Inc.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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