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charge pump driver for lcd white led backlights adm8845 rev. c information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. specifications subject to change without notice. no license is granted by implication or otherwise under any patent or patent rights of analog devices. trademarks and registered trademarks are the property of their respective owners. one technology way, p.o. box 9106, norwood, ma 02062 - 9106, u.s.a. tel: 781.329.4700 www.analog.com fax: 781.461.3113 ? 200 4C 201 1 analog devices, inc. all rights reserved. f eatures d rives 6 leds from 2.6 v to 5.5 v (li -i on) input supply 1 /1.5 /2 f ractional charge pump to maximiz e power efficiency 1% m ax led current matching up to 88% power efficiency over li -i on ran ge powers main and sub displa y leds with individual shutd own package footprint only 9 mm 2 (3 mm 3 mm) package height only 0.9 mm low power shutdown mode shutdown f unction soft - start limiting in - rush current a pplications cellular phones with main and sub displays white led b acklighting camera flash/strobes and movie lights micro tft color displays dsc pda s ge neral description the adm8845 uses charge pump technology to p rovide the power required to drive up to six leds . the leds are used for backlighting a color lcd display , having regulated constant current for uniform brightness intensity . the main display can have up to four leds, and the sub display can have one or two leds . t he digital ctrl1 and ctrl2 input control pins control the shutdown operation and the brightness of the main and sub displays. to maxim ize powe r efficiency, the charge pump can operate in a 1 , 1.5 , or 2 mode. the charge p ump automatically switches between 1 /1.5 /2 modes , based on th e input voltage, to mai ntain sufficient drive for the led anodes at the high est power efficiency. impro ved brightness matching of the leds is achieved by a feedback pin to sense individual led current with a maximum matching accuracy of 1%. f unctional block diag ram current control 1 current control 2 current control 3 current control 4 current control 5 current control 6 control logic v ref charge pump 1/1.5/2 mode osc led current control circuit fb1 current controlled sinks fb2 fb3 fb4 fb5 fb6 v out c4 4.7f v cc c1 1f ctrl1 ctrl2 c2 1f r set i set gnd c3 2.2f adm8845 04867-0-001 main sub figure 1.
adm8845 rev. c | page 2 of 20 table of contents features .............................................................................................. 1 applications ....................................................................................... 1 general description ......................................................................... 1 functional block diagram .............................................................. 1 revision history ............................................................................... 2 specifications ..................................................................................... 3 absolute maximum ratings ............................................................ 4 thermal characteristics .............................................................. 4 esd caution .................................................................................. 4 pin configuration and function descriptions ............................. 5 typical performance characteristics ............................................. 6 theory of operation ...................................................................... 10 output current capability ........................................................ 11 automatic gain control ............................................................ 11 current matching ....................................................................... 11 brightness control with a digital pwm signal ..................... 11 led brightness control using a pwm signal applied to v pwm ............................................................................................. 13 led brightness control using a dc voltage applied to v bright .......................................................................................... 13 applications ..................................................................................... 14 la yout considerations and noise ............................................ 14 white led shorting .................................................................. 14 driving fewer than six leds ................................................... 14 driving flash leds .................................................................... 15 driving camera light, main, and sub leds .......................... 15 driving four backlight white leds and fl ash leds ........... 16 power efficiency ......................................................................... 17 outline dimensions ....................................................................... 18 ordering g uide .......................................................................... 18 r evision h istory 1 /1 1 rev. b to rev. c changes to figure 18 and figure 19 ................................................ 8 changes to ordering guide ........................................................... 18 4 /10 rev. a to rev. b changes to figure 2 ........................................................................... 5 changes to figure 4 ........................................................................... 6 changes to figure 16 to figure 19 ................................................... 8 changes to brightness control with a digital pwm signal section ................................................................................... 11 added exposed pad notation to outline dimensions .............. 18 changes to ordering guide ........................................................... 18 7 /0 5 re v. 0 to rev. a changes to table 3 ............................................................................. 5 changes to table 7 ........................................................................... 12 updated outline dimensions ........................................................ 18 changes to ordering guide ........................................................... 18 10/04 revision 0: initial version
adm8845 rev. c | page 3 of 20 specifications v cc = 2.6 v to 5.5 v; t a = ? 40 c to + 85 c, unless otherwise n oted; c1, c2 = 1.0 f; c3 = 2.2 f ; c4 = 4.7 f . table 1. parameter min typ max unit test conditions inpu t v o ltage , v cc 2.6 5.5 v supply current , i cc 2.6 5 m a all six leds d isabled , v cc = 3.3 v, r set = 7.08 k? ctrl1 = 1, crtl2 = 1 shutdown current 5 a charge pump frequency 1.5 mh z charge pump mode thresholds 1.5 to 2 3.33 v accuracy 4 % 2 to 1.5 3.36 v accuracy 4 % hysteresis 4 0 m v 1 to 1.5 4.77 v accuracy 4 % 1.5 to 1 4.81 v accuracy 4 % hysteresis 40 m v i set pin led : led matching ?1 +1 % i led = 20 ma, v fb =0.4 v led : i set accuracy ?1 +1 % i led = 20 ma, r set = 7.08 k?, v fb = 0.4 v , v cc = 3.6 v , t a = 25 c i set pin voltage 1.18 v i led to i set ratio 120 min compliance on fb x p in 0.2 0.3 v i set = 20 ma charge pump output resi stance 1.2 1. 8 ? 1 m ode 3.5 5.1 ? 1.5 m ode 8.0 14 ? 2 m ode led current 30 m a guaranteed by design. not 100% production tested. see figure 21 . pwm 0.1 200 k hz digital inputs input hi gh 0. 5 v cc v input low 0.3 v cc v input leakage current 1 a charge pump power efficiency 88 % ctrl1 = 1, crtl2 = 1, v cc = 3.4 v, v fb = 0.2 v, i fb = 20 ma v out ripple 30 m v v cc = 3.6 v, i led = 20 ma, a ll six leds e nabled
adm8845 rev. c | page 4 of 20 absolute maximum ratings t a = 25c, unless otherwise noted . table 2. parameter rating supply voltage , v cc C 0.3 v to +6.0 v i set C 0.3 v to +2 .0 v ctrl1, ctrl2 C 0.3 v to +6.0 v v out s horted 1 indefinite feedback p ins fb1 to fb6 C 0.3 v to +6.0 v operating temperature range six leds e nabled with 30 ma/led 2 C 40c to +6 5c six leds e nabled with 20 ma/led 2 C 40c to +8 5c v out 3 180 ma storage temperature range C 65c to +125c power dissipation 2 mw esd class 1 1 short through led. 2 led current shou ld be derated above t a > 65c, refer to figure 21 . 3 based on long - term current density limitations. stresses above those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. thermal characterist ics 16- lead lfcsp package: ja = 50c/w esd caution esd (electrostatic discharge) sensitive devic e. electrostatic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge without detection. although this product features proprietary esd protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd precautions are recommended to avoid performance degradation or loss of functionality.
adm8845 rev. c | page 5 of 20 pin configuration and function description s pin 1 indic at or 1v out 2 c2+ 3i set 4 fb1 11 c2? 12 ctrl2 10 gnd 9 fb6 notes 1. connect exposed p addle t o gnd. 5 fb2 6 fb3 7 fb4 8 fb5 15 v cc 16 c1+ 14 c1? 13 ctrl1 top view (not to scale) adm8845 04867-0-003 figure 2 . pin configuration ta ble 3. pin function descriptions pin no. mnemonic function 1 v out charge pump output. a 2.2 f capacitor to ground is required on this pin. connect v out to the anode s of all the leds. 2 c2+ flying capacitor 2 positive connect ion . 3 i set bia s current set inp ut. the current , i set , flowing through the resistor , r set , is gained up by 120 to give the i led cur r ent. connect r set to gnd to set the bias current as v set /r set . note that v set = 1.18 v. 4 to 9 fb1 to fb6 led1 to led6 cathode c onnection and charge pump feedback. the current , i set , flowing in these leds is 120 times the current flowing through resistor , r set . when using fewer than six leds, this pin can be left unconnected or connected to gnd. 10 gn d device ground pin . 11 c2 ? flying capacitor 2 negative connection. 12 ctrl2 digital input. 3 v cmos logic. used with ctrl1 to control the shu tdown operation of the main and sub leds. 13 ctrl1 digital input. 3 v cmos logic. used with ctrl2 to control the shutdown operation of the main and sub leds. 14 c1 ? flying capacitor 1 negative connection. 15 v cc positive supply voltage input. connect this pin to a 2.6 v to 5.5 v supply with a 4.7 f decoupling capacitor. 16 c1+ flying capacitor 1 positive connection. - ep expose d paddl e. connect the exposed paddle to gnd.
adm8845 rev. c | page 6 of 20 typical performance characteristics 5 10 15 20 25 30 35 10.75 04867-0-004 r set (k ? ) led current (ma) 4.75 6.75 12.75 14.75 8.75 figure 3. i led (ma) current vs. r set 20.00 20.10 20.15 20.20 20.25 20.30 20.35 4.1 04867-0-005 supply voltage (v) led current (ma) 2.6 3.1 4.6 5.6 3.6 5.1 ?40 ?c 25 ?c 85 ?c 20.05 figure 4. i led (ma) vs. temperature (c), six leds enabled ?0.3 ?0.2 ?0.1 0 0.1 0.2 0.3 25 04867-0-006 temperature ( ?c) % error ?40 ?20 45 85 0 65 figure 5. i led matching (%) over temperature (c), v cc = 3.6 v, i led = 20 ma, six leds enabled ?0.4 ?0.2 ?0.1 0 0.1 0.2 0.4 3.8 04867-0-007 supply voltage (v) matching error (%) 2.6 4.2 5.0 3.4 4.6 ?0.3 0.3 3.0 5.4 max negative matching error max positive matching error figure 6. i led (ma) matching error (%) vs. supply voltage (v), t a = 25c and i led = 20 ma 04867-0-008 temperature ( ?c) led current (ma) ?40 0 80 40 20.08 20.12 20.14 20.16 20.18 20.20 20.24 20.10 20.22 figure 7. i led (ma) variation over temperature (c), v cc = 3.6 v 5 10 15 20 25 30 35 3.8 04867-0-009 supply voltage (v) led current (ma) 2.6 3.0 4.6 5.4 3.4 5.0 4.2 figure 8. i led (ma) vs. supply voltage (v)
adm8845 rev. c | page 7 of 20 0 4 8 12 16 20 04867-0-010 duty cycle (%) led current (ma) 0 20 60 100 80 40 figure 9. i led (ma) vs. pwm dimming (varying duty cycle), six leds enabled, frequency = 1 khz 0 50 100 150 250 300 04867-0-011 supply voltage (v) supply current i cc (ma) 2.6 3.0 3.8 4.6 4.2 3.4 20ma/led 15ma/led 200 5.0 5.4 figure 10 . input current vs. supply voltage, six leds enabled 04867-0-012 ch2 20.0mv ch1 20.0mv m 400ns ch1 220mv 2 1 b w b w v out v cc figure 11 . 1.5 mode operating waveforms 60 65 70 80 90 95 04867-0-013 duty cycle (%) efficiency (%) 0 40 60 8070 50 85 90 100 10 20 30 75 figure 12 . led efficiency vs. varying duty cycle of 1 khz pwm signal, six leds enabled, 20 ma/led 04867-0-014 ch2 160ma ch1 2.00v m 5.00 s ch2 180mv 2 1 b w b w current 3 v out ctrl1/2 ch3 1.00v figure 13 . soft start showing the initial in - rush current and v out variation, six leds @ 20 ma/led, v cc = 3.6 v 04867-0-015 ch2 20.0mv ch1 20.0mv m 400ns ch1 220mv 2 1 b w b w v out v cc figure 14 . 2 mode operating waveform
adm8845 rev. c | page 8 of 20 04867-0-016 ch2 20.0mv ch1 20.0mv m 400ns ch1 220mv 2 1 b w b w v out v cc figure 15. 1 mode operating waveforms 40 45 50 60 80 90 04867-0-017 v cc (v) power efficiency (%) 70 55 65 75 85 v f = 4.0v v f = 3.8v v f = 4.3v v f = 3.2v v f = 3.6v 2.8 3.0 3.4 3.8 3.6 3.2 4.0 4.2 2.9 3.1 3.3 3.5 3.7 3.9 4.1 figure 16. power efficiency vs. supply voltage over li-ion range, six leds @ 15 ma/led 40 45 50 60 80 90 04867-0-018 v cc (v) power efficien c y (%) 70 55 65 75 85 v f = 4.0v v f = 3.8v v f = 4.3v v f = 3.2v v f = 3.6v 2.8 3.0 3.4 3.8 3.6 3.2 4.0 4.2 2.9 3.1 3.3 3.5 3.7 3.9 4.1 figure 17. power efficiency vs. supply voltage over li-ion range, four leds @ 15 ma/led 40 45 50 60 80 90 04867-0-019 v cc (v) power efficien c y (%) 70 55 65 75 85 v f = 4.0v v f = 3.8v v f = 4.3v v f = 3.2v v f = 3.6v 2.8 3.0 3.4 3.8 3.6 3.2 4.0 4.2 2.9 3.1 3.3 3.5 3.7 3.9 4.1 figure 18. power efficiency vs. supply voltage over li-ion range, six leds @ 20 ma/led 40 45 50 60 80 90 04867-0-020 v cc (v) power efficien c y (%) 2.8 3.0 3.4 3.8 3.6 3.2 70 4.0 4.2 55 65 75 85 2.9 3.1 3.3 3.5 3.7 3.9 4.1 v f = 4.0v v f = 3.8v v f = 4.3v v f = 3.2v v f = 3.6v figure 19. power efficiency vs. supply voltage over li-ion range four leds @ 20 ma/led 04867-0-021 ch1 2.00v ch2 2.00v m10.0ms ch2 4.36v 2 1 v out ctrl1/2 ? : 44.0ms @: ?44.4ms c2 fall 200 ? s low signal amplitude figure 20. tpc delay
adm8845 rev. c | page 9 of 20 04867-0-022 30ma 20ma 65c 85c figure 21 . maximum i led (ma) vs. ambient temperature, six leds connected
adm8845 rev. c | page 10 of 20 the ory of operation the adm8845 charge pump driver for lcd white led back - lights implements a multiple gain charge pump (1 , 1.5 , 2) to maintain the correct voltage on the anodes of the leds over a 2.6 v to 5.5 v (li -i on) input supply voltage. the charge pump automatically switches between 1 /1.5 /2 modes , based on the input voltage, to maintain sufficient drive for the led anodes, with v cc input voltages as low as 2.6 v. it also includes regula - tion of the charge pump output voltage for supply voltages up to 5.5 v. the six le ds of the adm8845 are arranged into two groups, ma in and sub. the main display can have up to four leds, fb1 to fb4 , and the sub display can have one or two leds, fb5 and fb6 ( see figure 23 ). tw o digital input control pins, ctrl1 and ctrl2 , control the shutdown operation and the brightness of the ma in and sub displays ( see table 4 ). table 4. shutdown truth table ctrl1 ctrl2 led shutdown operation 0 0 sub display off/ main display off 0 1 sub display off/ main display on 1 0 sub dis play on/main display off 1 1 sub display on/main display on an external resistor , r set , is connected between the i set pin and gnd. t his resistor sets up a reference current , i set , which is internally gained up by 120 within the adm8845 to produce the i led currents of up to 30 ma/led (i led = i set 120 and i set = 1.18 v /r set ). the adm8845 uses six individual current sinks to individually sense each led current with a maximum matching performance of 1%. this current matching perform - ance ensures uniform brightness across a color display. the adm8845 lets the user control the brightness of the white leds with a d igital pwm signal applied to ctrl1 and/or ctrl 2 . the duty cycle of the applied pwm signal determines the brightness of the main and/or sub displa y backlight white leds. the adm8845 also allows the brightness of the white leds to be controlled using a dc voltage ( see figure 22) . s oft - start circuitry limit s the in - rush current flow at power - up. the adm8845 is fabricated using cmos technology for minimal power consumption and is packa ged in a 16 -l ead lead frame chip scale pac kage. i set r set = 13.4k? r = 15k? v bright 0v?2.5v adm8845 04867-0-027 figure 22 . pwm brightness control using a dc voltage a pplied to v bright current control 1 current control 2 current control 3 current control 4 current control 5 current control 6 control logic v ref charge pump 1/1.5/2 mode osc led current control circuit fb1 current controlled sinks fb2 fb3 fb4 fb5 fb6 v out c4 4.7f v cc c1 1f ctrl1 ctrl2 c2 1f r set i set gnd c3 2.2f adm8845 04867-0-001 main sub figure 23 . functional block diagram
adm8845 rev. c | page 11 of 20 output current capab ility the adm8845 can drive up to 30 ma of current to each of the six leds given an input voltage of 2.6 v to 5.5 v. t h e l e d currents have a max imum current matching of 1% between any two led curre nts. an external resis tor , r set , sets the output current, approximated by the following equation: r set = 120 (1.18 v/ i led ) to regulate the led currents properly, sufficient headroom voltage (compliance) must be present. the compliance refers to the minimum amount of voltage t hat must be present across the internal current sinks to ensure that the desired current and matching per formance can be realized. to ensure that the de sired current is obtained, use the following equation to find the minimum input voltage required: v out ? v f compliance where v f is the led forward voltage. for 20 ma/led , the complian ce is 0. 20 v typ and 0.3 0 v max ( see table 5 ). table 5 . i led , r set , and compliance table i led r set typ com pliance 15 ma 9.4 4 k ? 0.17 v 20 ma 7.08 k ? 0.2 0 v 30 ma 4.72 k ? 0.34 v when the adm8845 charge pump is loaded with 180 ma (six leds at 30 ma/led) , the ambient operating temper ature is reduced ( see figure 21 ). automatic gain contr ol the automati c gain control block controls the operation of the charge pump by selecting the appropriate g ain for the c harge p ump . this mai ntain s sufficient drive for the led anodes at the high est power efficiency over a 2.6 v to 5.5 v input supply range . the charge pu mp s witching threshol ds are described in table 6 . table 6 . charge pump switching thresholds gain threshold 1.5 to 2 3.33 v 2 to 1.5 3.36 v 1 to 1.5 4.77 v 1.5 to 1 4.81 v current matching th e 1% max imum current matching performance is defined by the following equations: i avg = ( i max + i min )/2 max matching error = [( i max ? i avg )/ i avg ] 100 or min matching error = [( i min ? i avg )/ i avg ] 100 w here i max is the largest i led current , and i min is the smallest i led current. brightness control w ith a digital pwm signal pwm brightness control provides the widest brightness control method by pulsing the white leds on and off using the digital input control pins, ctrl1 and /or ctrl2. pwm brightness contr ol also removes any chromaticity shifts associated with ch anging the white led current, because t he leds operate either at zero current or full current (set by r set ). the digital pwm signal applied with a frequency of 100 hz to 200 khz turns the current c ontrol sinks on and off using ctrl1 and/or ctrl2 . the average current through the leds changes with the pwm signal duty cycle. if the pwm frequency is much less than 100 h z, flicker could be seen in the leds. for the adm8845, zero duty cycle turn s off the leds , and a 50% duty cycle result s in an average led current i led being half the pro - grammed led current. for example, if r set is set to program 20 ma/led, a 50% duty cycle result s in an average i led of 10 ma /led , i led being half the programmed led current . fb1 fb2 fb3 fb4 fb5 fb6 v out c1 1f ctrl1 ctrl2 c2 1f r set i set c3 2.2f adm8845 pwm input or high/low pwm input or high/low 04867-0-024 figure 24 . digital pwm brightness control application diagram by applying a digital pwm signal to the digital input cont rol pins, ctrl1 and/or ctrl2 can adjust the brightness of the sub and /or main displays. the six white leds of the adm8845 are organized into two groups: main disp lay, fb1 to fb4, an d sub display, fb5 and fb6. for more information, refer to the theory of operation section .
adm8845 rev. c | page 12 of 20 the main and sub display brightness of the adm8845 can be cont rolled together or separately b y applying a digital pwm signal to both ctrl1 and ctrl2 pins. the duty c ycle of the applied digital pwm signal determines the brightness of the main and sub displays together. v arying the duty cycl e of the applied pwm signal also varies the brightness of the main and sub displays from 0% to 100%. by holding ctrl1 low and applying a digital pwm signal to ctrl2, the sub display is turned off and the main display is turned o n. the brightness of the main display is then dete rmined by the duty cycle of the applied digital pwm signal. by applying a digital pwm signal to ctrl1 and holding ctrl2 low, the sub display is turned on and the main display is turned off. then the brightness of the sub display is determined by the duty cycle o f the applied digital pwm signal. by applying a digital pwm signal to ctrl1 and holding ctrl2 high, the sub display is turned on and the main display is turned on. then the brightness of the sub display is determined by the duty cycle of the applied digita l pwm signal. the brightness of the main display is set to th e maximum, which is set by r set . by holding ctrl1 high and applying a digital pwm signal to ctrl2, the sub display is turne d on and the main display is turned on. then the brightness of the main display is determined by the duty cycle of the applied digital pwm signal. the bright - ness of the sub display is set to the maximum , which is set by r set . when ctrl1 and ctrl2 go low , the led current control sinks shutdown. shutdown of t he charge pump i s d elayed by 15 ms . this timeout period (t cp ) allows the adm8845 to determine if a digital pwm signal is present on ctrl1 and ctrl2 or if the user has selected a full chip shutdown ( see figure 25 ). if d igital pwm brightness control of the leds is not required , a constant logic l eve l 1 (v cc ) or 0 (gnd) must be applied . the six white led s in the adm8845 are arranged in two groups, sub and main. it is possible to configure the six leds as in table 7 . for more in formation, also r efer to figure 25. table 7 . digital inputs truth table ctrl1 ctrl2 led operation 0 0 sub display off/ main display off (full shutdown) 1 0 , 2 1 sub display off/ main display on 1 , 3 1 0 sub display on/main display off 4, 2 1 1 sub display on/main display on (full on) 4 , 3 0 pwm sub display off/digital pwm brightness control on main display 1 , 5 pwm 0 digital pwm br ightness control on sub display/ main display off 5 , 2 1 pwm sub display on/ digital pwm brightnes s control on main display 4 , 5 pwm 1 digital pwm br ightness control on sub display/main display on 5 pwm pwm digital pwm brightness control on sub and main d isplay 5 1 sub display off means the sub display leds only is off. ctrl1 = 0 means a constant logic level (gnd) is applied to ctrl1. 2 ma in display off means the main display only is off. ctrl2 = 0 means a constant logic level (gnd) is applied to ctrl2. 3 main display on means the display is on with the maximum brightness set by the r set resistor. ctrl2 = 1 means a constant logic level (v cc ) is applied to ctrl2. 4 sub display on means the display is on with the maximum brightness set by the r set resistor. ctrl1 = 1 means a constant logic level (v cc ) is applied to ctrl1. 5 pwm means a digital pwm signal is applied to the ctrl1 and/or the ctrl 2 pin with a frequency from 100 hz to 200 khz.
adm8845 rev. c | page 13 of 20 led config. full on main and sub off ctrl1 ctrl2 v out i led (sub) i led (main) sub display brightness main display brightness 37ms > t cp > 15ms shdn shdn 50% 50% 100% 100% 80% t cp 04867-0-025 sub and main 50% duty cycle main 80% duty cycle, sub off figure 25 . application timing led brightness contr ol using a pwm signal applied to v pwm ad ding two external resistors and a capacitor , as shown i n figure 26, can also be used to control pwm brightness . this pwm brightness control method can be used instead of ctrl1 and/or ctrl2 digital pwm brightness control. w ith this con - figuration , t he ctrl1 and ctrl2 digital logic pins can be used to control shutdown of the white leds , while v pwm can be used to control the brightness of all the white leds b y applying a high frequency pwm signal ( a mplitude 0 v to 2.5 v) to drive an r -c- r filter on the i set pin of the adm8845 . a 0% pwm duty cycle corresponds to 20 ma/led, whil e a 100% pwm duty cycle corresponds to a 0 ma/led. at pwm frequencies above 5 khz, c5 may be reduced ( see figure 26) . t o ha ve 20 ma flowing in each led, the amplitude of the pwm signal must be 0 v and 2.5 v only. 100 ) 1( 120 2 2 _ cycle duty rr rr voltage i i set set set led ? + = i set r set = 13.4k? r = 7.5k? v pwm 0v?2.5v adm8845 04867-0-026 100% = i led = 0ma 0% = i led = 20ma r = 7.5k? c5 = 1f figure 26 . pwm br ightness control u sing filtered pwm sign al led brightness contr ol using a dc voltage applied to v bright by a dding one resistor, as in figure 22 , this configuration can control th e brightness of the white leds using a dc voltage applied to the v bright node. figure 27 shows an application example of led b rightness control using a dc v oltage with a amplitude of 0 v to 2.5 v, applied to v bright . the equation for i led is i set = [ (1/ r set + 1/ r )(v set )] C [ (1/ r )( v bright )] i led = 120 i set w here r = 15 k? and v set = voltage at i set pin (1.18 v) . v bright 04867-0-028 i led 2.5v 0ma 1.6v 7.2ma 0.8v 13.6ma 0v 20ma figure 27 . pwm brightness control application diagram using a dc voltage applied to v bri ght
adm8845 rev. c | page 14 of 20 applications layout consideration s and noise because of the s switching behavior of the adm8845, pcb trace layout is an important consideration. to ensure optimum performance, a ground plane should be used, and all capacitors (c1, c2, c3, c4) must be located with minimal track lengths to the pins of the adm8845. white led shorting if an led is shorted, the adm8845 continues to drive the remaining leds with i led per led (i led = i set 120 ma). this is because the adm8845 uses six internal currents sinks to produce the led current. if an led is shorted, the adm8845 continues to sink (i set 120 ma) as programmed by r set through the shorted led. driving fewer than s ix led s the adm8845 can be operated with fewer than six leds in parallel by simply leaving the unused fbx pins floating or connected to gnd. for example , figure 28 shows five leds being powered by the adm8845, and figure 29 shows three main leds and one sub led. v out fb1 fb2 fb3 fb4 fb5 fb6 v cc 2.6v?5.5v ctrl1 ctrl2 gnd adm8845 04867-0-029 lcd figure 28 . driving five white leds v out fb1 fb2 fb3 fb4 fb5 fb6 v cc 2.6v?5.5v ctrl1 ctrl2 gnd adm8845 r set i set 04867-0-030 main display sub display figure 29 . driving three main leds and one sub led v out fb1 fb2 fb3 fb4 fb5 fb6 v cc 2.6v?5.5v ctrl1 ctrl2 gnd adm8845 r set i set 04867-0-002 main display sub display figure 30 . typical application diagram
adm8845 rev. c | page 15 of 20 driving flash led s the adm8845 can be operated with any two fbx pins used in parallel to double the combined led current supplied by the adm8845. for example , if three f lash leds need to be driven with 60 ma/led, the adm8 845 can be configured as in figure 31 (see also figure 21 ). v out fb1 fb2 fb3 fb4 fb5 fb6 v cc 2.6v?5.5v ctrl1 ctrl2 gnd adm8845 r set 4.27k? 04867-0-031 60ma 60ma 60ma figure 31 . driving three flash leds driving camera light , main , and s ub led s the adm8845 can be configur ed to power a camera light that is com posed of four white leds in parallel, along with the main and sub display bundled in to one package . fb1 to fb4 now power the camera light , and fb5 and fb6 power the main display. the sub display led is powered from the adm8845 by using an external current mirror to control the current flowing through the sub white led ( see figure 32 ) . al l white leds have 15 ma/led. t otal load on the adm8845 charge pump is therefore 105 ma, and the max i mum load on the adm8845 c harge pump i s 180 ma ( see figure 21 ). ?? current control 1 current control 2 current control 3 current control 4 current control 5 current control 6 control logic v ref charge pump 1/1.5/2 mode osc led current control circuit fb1 current controlled sinks fb2 fb3 fb4 fb5 fb6 v out c4 4.7f vcc c1 1f ctrl1 ctrl2 c2 1f r set 9.44k? i set gnd c3 2.2f adm8845 04867-0-032 15ma/led 15ma/led 15ma/led current control7 r camera main sub figure 32 . drivi ng camera light, t wo main leds, and o ne sub led
adm8845 rev. c | page 16 of 20 driving four backlight whi te led s and flash led s the adm8845 can be configured to power four backlight w hite leds and a camera flash, bundled into one package. fb1 to fb4 power the backlight li ght , fb5 and fb6 power two of the f lash leds , while the third is powered by an external c urrent mirror to control the current flowing t hrough the third flash led ( see figure 33) . all the backlight white leds have 15 ma/led, and the flash c urrent is 20 ma/led. t he total load on the adm8845 charge pump is 120 ma; the max imum load on the adm8845 charge pump is 180 ma ( see figure 21 ). ctrl1 controls the f lash on/off , and ctrl2 controls the back - light on/off and bright ness control. because the r set resistor sets the current that each of the six current control blocks can sink, a pwm signal is used to change the current in the backlight from 20 ma to 5 ma/led. the ctrl 2 duty cycle is 15/20 to give 15 ma/ backlight led. 04867-0-034 current control 1 current control 2 current control 3 current control 4 current control 5 current control 6 control logic v ref charge pump 1/1.5/2 mode osc led current control circuit fb1 current controlled sinks fb2 fb3 fb4 fb5 fb6 v out c4 4.7f v cc ctrl1 ctrl2 c2 1f c1 1f r set 7.32k? i set gnd c3 2.2f adm8845 15ma/led 20ma/led current control 7 r back- light flash figure 33 . driving four backlight leds and flash led
adm8845 rev. c | page 17 of 20 power efficiency the adm8845 power efficiency ( ) e quations are = p out / p in p in = (( v cc i load gain ) + ( i q v cc )) p out = 6 ( v f i led ) where: i q is the q uiescent current of the adm8845, 2.6 ma. v f is the led forward voltag e. gain is equal to the charge p ump mod e (1 , 1.5 , 2 ). fb1 fb2 fb3 fb4 fb5 fb6 v out ctrl1 ctrl2 r set i set adm8845 04867-0-033 v cc 3.4v v cc gnd i load i in figure 34 . charge pump power efficiency diagram e xample s 1 and 2 show calculations of the adm 8845 power efficiency . s ee figure 34 as well . example 1 the adm8845 d riving six white led with 20 ma/led at v cc = 3.4 v (1.5 mode) , led v f = 4. 5 v. p in = (( v cc i load gain ) + ( v cc i q )) p in = ((3.4 120 ma 1.5) + (3.4 2.6 ma)) p in = ((0.612) + (0.00884)) p in = 0.62084 p out = 6 ( v f i led ) p out = 6 ( 4. 5 v 20 ma ) p out = 0.54 = p out / p in = 0.54 /0.62084 = 87 % example 2 the adm8845 driving six white led with 20 ma/led at v cc = 3.4 (1 .5 mode) , led v f = 3.6 v. p in = (( v cc i load g ain ) + ( v cc i q )) p in = ((3.4 120 ma 1.5) + (3.4 2.6 ma)) p in = ((0.612) + (0.00884)) p in = 0.62084 p out = 6 ( v f i led ) p out = 6 ( 3.6 v 20 ma ) p out = 0.432 = p out / p in = 0.432 / 0.62084 = 70 %
adm8845 rev. c | page 18 of 20 outline dimensions 1 0.50 bsc 0.60 max pin 1 indicator 1.50 ref 0.50 0.40 0.30 0.25 min 0.45 2.75 bsc sq top view 12 max 0.80 max 0.65 typ seating plane pin 1 indicator 1.00 0.85 0.80 0.30 0.23 0.18 0.05 max 0.02 nom 0.20 ref 3.00 bsc sq * 1.45 1.30 sq 1.15 exposed pad 16 5 13 8 9 12 4 (bottom view) * compliant to jedec standards mo-220-veed-2 except for exposed pad dimension. 072208-a for proper connection of the exposed pad, refer to the pin configuration and function descriptions section of this data sheet. figure 35 . 16 - lead lead frame chip scale package [lfcsp_vq] 3 mm x 3 mm body, very thin qu ad (cp - 16 - 2) dimensions shown in millimeters ordering guide model 1 temperature range package description package option branding adm8845acpz - reel ? 40 c to + 85 c 16- lead lfcsp _vq cp -16 -2 m5g adm8845acpz - reel7 ? 40 c to + 85 c 16- lead lfcsp _vq cp -16 -2 m5g adm8845eb - eval z evaluation board 1 z = rohs compliant part.
adm8845 rev. c | page 19 of 20 notes
adm8845 rev. c | page 20 of 20 notes ? 200 4C 201 1 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. d04867 -0-1/11(c)

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