led1 vout gnd iset led2 led3 led4 vin c2+ c2- en1 en2 c1+ c1- ctrl single-wire on/off and dimming control a8435 v batt 2.7 to 5.5 v rset c2 cin 1 f cout 1 f 1 f 1 f c1 a8435 led1 vout gnd iset led2 led3 led4 vin c2+ c2? en1 en nc 2 c1+ c1? ctrl on/off and dimming control v batt 2.7 to 5.5 v rset c2 cin 1 f cout 1 f 1 f 1 f c1 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 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 (1, 1.5), 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 3 mm qfn/mlp-16 package (es), fitting the needs of space-conscious applications. features and benefits ? proprietary adaptive control scheme (1, 1.5) ? 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 3 mm footprint ? very thin 0.75 mm nominal height package high efficiency charge pump white led driver package: 16 pin qfn/mlp (suffix es) typical applications a8435 approximate scale ? white led backlights for cellular phones, pdas ? digital cameras, camcorders ? portable audio devices ? other portable device white led backlighting ? 120 ma wled flash/torch applications include:
high efficiency charge pump white led driver a8435 2 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ab so lute max i mum rat ings package thermal characteristics input or output voltage vin, vout, c1+, c1?, c2+, and c2? pins ...................... ?0.3 to 6 v all other pins..................................................... ?0.3 to v in + 0.3 v vout short circuit to gnd .................................................... continuous operating ambient temperature, t a ..................................... ?40c to 85c maximum junction temperature, t j(max) ............................................. 150c storage temperature, t s ................................................... ?55c to 150c selection guide part number packaging* package type A8435EESTR-T 7-in. reel, 1500 pieces/reel es, 3 3 mm qfn/mlp-16 *contact allegro for additional packing options. package is lead (pb) free, with 100% matte tin leadframe plating. r ja = 68 c/w, on a 4-layer board (vendor data; unverified) additional information is available on the allegro web site. + ? + ? + ? + ? + ? + ? c1 fractional charge pump (1 and 1.5 ) vin rset led1 led2 led3 led4 en1 en2 vout c1+ c1 ? c2+ c2? iset gnd 1 f 1 f c2 1 f 1 f cin cout ctrl minimum select current mirror control, clock, and reference functional block diagram
high efficiency charge pump white led driver a8435 3 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com (top view) name pin number function* c1? 13 negative terminal of capacitor c1. c1+ 16 positive terminal of capacitor c1. c2? 15 negative terminal of capacitor c2. c2+ 1 positive terminal of capacitor c2. ctrl 4 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). en1 3 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.) en2 5 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.) ep ? exposed metal pad on bottom side. connect this to ground plane for better thermal performance. gnd 11 ground. iset 6 connect rset resistor to ground to set desired constant current through leds. led1 8 current sink for led1. connect to vin or vout if not used for led. (do not leave unconnected.) led2 7 current sink for led2. connect to vin or vout if not used for led. (do not leave unconnected.) led3 10 current sink for led3. always connect this pin to led. led4 9 current sink for led4. connect to vin or vout if not used for led. (do not leave unconnected.) nc 12 no connection. vin 14 power supply voltage input. vout 2 charge pump voltage source output for connection to the led anodes. * see application information section for cited figure and tables. terminal list table 12 11 10 9 nc gnd led3 led4 1 2 3 4 c2+ vout en1 ep ctrl 16 15 14 13 c1+ c2? vin c1? 5 6 7 8 en2 iset led2 led1 pin-out diagram
high efficiency charge pump white led driver a8435 4 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com electrical characteristics 1 v in = v en1 = v en2 = 3.6 v, c 1 = c 2 = 1 f, t a = ?40 to 85c, typical values at t a = 25c (unless otherwise noted) characteristics symbol test conditions min. typ. max. units input voltage range v in 2.7 ? 5.5 v undervoltage lockout threshold v uvlo v in falling, v uvlohys = 35 mv 2.25 2.45 2.60 v uvlo hysteresis window v uvlohys ? 35 ? mv quiescent current i q switching, t a = 25c ? 2.8 4 ma en1 = en2 = gnd, t a = 25c ? 0.1 1 a soft-start completion time t ss ? 2 ? ms iset bias voltage v isetbias 0.56 0.6 0.64 v iset leakage in shutdown v isetlkg ? 0.01 1 a iset current range i iset 40 ? 140 a iset to led x current ratio i led x / i iset i iset = 60 a, ctrl = open or high en1 = en2 = vin 190 219 245 a/a en1 = vin, en2 = gnd 105 121 137 a/a en1 = gnd, en2 = vin 51 60 69 a/a i iset = 60 a, ctrl = low full brightness ? 200 ? a/a i led accuracy e iled en1 = en2 = vin, r set = 4.3 k ? 0.9 ? % led current matching 2 i led v in =3.6 v, i led = 30 ma per led ? 0.5 ? % regulation voltage at ledx (1.5) v led en1 = en2 = vin ? 150 ? mv open loop output resistance 3 r out 1 mode: [(v in ? v out ) / i out ] ? 1.1 ? 1.5 mode: [(1.5 v in ? v out ) / i out ] ? 3.6 ? 1 to 1.5 mode transition voltage at ledx v trans v ledx falling ? 100 ? mv transition to dropout voltage difference 4 v dr measured as v trans ? v dropout ? 60 ? mv led leakage in shutdown v ledlkg en1 = en2 = gnd, v in = 5.5 v, t a = 25c ? 0.01 1 a oscillator frequency f osc ? 1 ? mhz output overvoltage protection 5 v ovp open circuit at any led that is programmed to be in the on state ? 5.74 ? v ctrl, en1, en2 input high logic threshold 6 v ih 1.6 ? ? v ctrl, en1, en2 input low logic threshold 6 v il ? ? 0.4 v input high current i ih v ih = v in ?? 1 a input low current i il v il = gnd ? ? 1 a en1 pulse low time 7 t lo 0.5 ? 500 s en1 pulse high time 7 t hi 0.5 ? ? s initial en1 pulse high time 7 t hi(init) first en1 pulse after shutdown 100 ? ? s shutdown delay 7 t shdn falling edge of en1 pulse ? 2 3 ms thermal-shutdown threshold t shdn 20c hysteresis ? 165 ? c 1 specifications guaranteed by design over operating temperature range, ?40c to 85c. 2 led current matching is defined as (i led x ? i led(avg) ) / i led(avg) . 3 the open loop output resistance for 1.5 mode is measured with one of the led x pins tied to ground or open (thus its voltage is always less than 80 mv). 4 dropout voltage, v dropout , is defined as the ledx-to-gnd voltage at which i led x drops 10% below the value of i led x at v led x = 200 mv. 5 guaranteed by design. 6 en2 is not used when ctrl is tied to ground. 7 applies only when ctrl is tied to ground. see figure 3 in application information section.
high efficiency charge pump white led driver a8435 5 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com performance characteristics tests performed using application circuit shown in figure 1: dual wire control; and v in = 3.6 v, en1 = en2 = vin, c in = c 1 = c 2 = c out = 1 f, r set = 7.5 k , t a = 25c (unless otherwise noted) 50 60 70 80 90 100 2.70 2.90 3.10 3.30 3.50 3.70 3.90 4.10 v in (v) (%) 4.75 9.8 17.6 (full brightness) dimming level (ma) 0 20 40 60 80 100 120 2.70 2.90 3.10 3.30 3.50 3.70 3.90 4.10 v in (v) i batt (ma) v in rising v in falling 17.6 ma 9.8 ma 4.75 ma v in rising v in falling v in rising v in falling 10 11 12 13 14 15 16 17 18 19 20 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 v in (v) i led (ma) efficiency versus supply voltage over range of dimming levels, v in falling supply current versus supply voltage over range of dimming levels (ma) led current versus supply voltage matching between leds <1% over range of v in
high efficiency charge pump white led driver a8435 6 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com t t v en t startup response 2-bit (en1-en2) dimming response 11-level single-wire serial dimming response i batt v out i out v en v en1 i out v out symbol parameter units/division c1 v en 5 v c2 i batt 50 ma c3 v out 2 v t time 500 s c2 c3 c1 symbol parameter units/division c1 v en1 2 v c2 i out 50 ma c3 v out 2 v t time 10 ms conditions en2 = ctrl = gnd, apply control signal to en1 c2 c1 c2 c1 c3 symbol parameter units/division c1 v en1 2 v c2 i out 50 ma t time 5 s conditions en2 = vin
high efficiency charge pump white led driver a8435 7 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com setting led current the led current level, i led x , is set by the value chosen for the external resistor, rset, which is connected to the iset terminal. the full current (100%) level for i led x can be calculated using the following formulas: setting formula ctrl = open or high r set ( ) = 0.6 v 219 / i led x ctrl = low r set ( ) = 0.6 v 200 / i led x 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 t lo 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 (t lo = ). application information table 1. ctrl, en1, and en2 pin states ctrl en1 en2 brightness led current, i led open or high low low shutdown 0 open or high low high 27% brightness 60 i iset open or high high low 55% brightness 121 i iset open or high high high full brightness 219 i iset low pulse input no effect adjustable; 11 levels of dimming from 100% to 5% (see figure 3; 100% cor- responds to 200 i iset ) low low > 2 ms low shutdown
high efficiency charge pump white led driver a8435 8 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 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 t shdn (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. shdn t shdn en1 0 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 5% 100% 90% t hi t lo t ss shdn t hi(init) i iled x 12345 67891011 figure 3. single-wire serial dimming control, at pin en1; ctrl = low, en2 = low.
high efficiency charge pump white led driver a8435 9 allegro microsystems, inc. 115 northeast cutoff, box 15036 worcester, massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com package es, 3 3 mm 16-pin qfn/mlp 0.30 0.18 .012 .007 0.50 0.30 .020 .012 0.80 0.70 .031 .028 0.05 0.00 .002 .000 3.15 2.85 .124 .112 3.15 2.85 .124 .112 0.20 ref .008 a b c seating plane c 0.08 [.003] 16x 16x 0.10 [.004] m c a b 0.05 [.002] m c 0.50 .020 a terminal #1 mark area b exposed thermal pad (reference only, terminal #1 identifier appearance at supplier discretion) 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 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) 16 2 1 a 16 1 2 b 1.70 nom .067 1.70 nom .067 0.23 x 0.23 ref .009 x .009 1.70 nom .067 1.70 nom .067 0.30 nom .012 1 16 4x 12x 0.20 min .008 16x 0.20 min .008 0.50 nom .020 0.90 nom .035 0.20 min .008 3.10 nom .122 3.10 nom .122 c 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 de par tures from the detailed spec i fi ca tion s as may be required to per- mit improvements in the per for mance, 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 sys tems without express written approval. the in for ma tion in clud ed herein is believed to be ac cu rate and reliable. how ev er, allegro microsystems, inc. assumes no re spon si bil i ty for its use; nor for any in fringe ment of patents or other rights of third parties which may result from its use. copyright?2005, 2006 allegromicrosystems, inc.
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