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1 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 general description the aat2847 is a highly integrated power solution for single cell li-ion/polymer based liquid crystal display (lcd) display applications. it includes a four channel light emitting diode (led) backlight driver and two inte- grated 200ma low dropout voltage regulators (ldos) as additional power supplies for display and camera related chipsets. the backlight driver in the aat2847 is a low noise tri- mode dc/dc charge pump converter. each of the four channels of the backlight driver is capable of delivering up to 20ma of bias currents for white leds. the white led (wled) backlight bias current matching is 1% which helps provide uniform display brightness. skyworks' as 2 cwire? (advanced simple serial control?) serial digital interface is used to enable, disable, and set the current for each backlight led channel. each led channel has sixteen available current level settings in three separate current scales, plus four available current level settings on a low level current scale. each led channel is equipped with built-in short circuit protection and auto disable functionality. a low shutdown current feature disconnects the load from the input and reduces quiescent current to less than 1 a. the aat2847 is available in the thermally enhanced 20-pin 3x4x0.75mm tqfn package. features input supply voltage range: 2.7v to 5.5v tri-mode (1x/1.5x/2x) charge pump: ? delivers up to 120ma of output current integrated lcd display solution: ? four-channel wled backlight user-programmable wled current scales: 30ma, 20ma and 15ma. ? sixteen programmable current level settings user selectable low level current scale ? four programmable current level settings ? dual 200ma ldos (w/separate enables) single-wire as 2 cwire serial interface for configuration/ control? four addressable registers ? fast, 1mhz serial interface > 90% peak efficiency ldo output voltages: ? aat2847-ee: user-programmable ? aat2847-qg: 2.8v and 1.5v ? aat2847-qi: 2.8v and 1.8v over-temperature protection available in 3x4x0.75mm tqfn34-20 package -40c to +85c temperature range applications camera function power supplies camera phone displays lcd modules white led backlighting typical application c1 1f c2 1f c1- c1+ c2- c2+ in out d1d2 d3 d4 200ma ldoa v bat 3.6v c in 2.2f aat 2847-ee en/set as 2 cwire backlight control c out 1f c ldoa 2. 2f 200ma ldob c ldob 2. 2f in fbafbb wleds osram lw m673 or equivalent gnd pgnd ena ldo a enable enb ldo b enable c1 1f c2 1f c1- c1+ c2- c2+ in out d1d2 d3 d4 v outa 2.8v, 200ma ldoa v bat 3.6v c in 2.2f aat 2847-qi gnd en/set as 2 cwire backlight control c out 1f c ldoa 2.2f ldob c ldob 2. 2f ena ldo a enable in wleds osram lw m673 or equivalent v outb 1.8v, 200ma enb ldo b enable pgnd downloaded from: http:///
2 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 pin descriptions pin # symbol function aat2847-ee aat2847-qg/qi 1d 2 d 2 led2 current channel input. connect to the cathode of backlight led 2. if not used, connect d2 to the out pin. 2d 1 d 1 led1 current channel input. connect to the cathode of backlight led 1. if not used, connect d1 to the out pin. 3 ldob ldob output of ldob. 4, 6 in in input voltage supply connection. 5 pgnd pgnd power ground. 7 fba nc aat2847-ee: feedback pin of ldoa. internally regulated at 1.2v. aat2847-qg/qi: no connection. do not make any connection to this pin. 8 ldoa ldoa output of ldoa. 9 c2- c2- negative terminal of ? ying capacitor 2. 10 c2+ c2+ positive terminal of ? ying capacitor 2. 11 out out charge pump output to drive load circuit. connect a 1 f or larger ceramic ca- pacitor between out and pgnd. 12 c1- c1- negative terminal of ? ying capacitor 1. 13 c1+ c1+ positive terminal of ? ying capacitor 1. 14 en/set en/set as 2 cwire control pin for backlight led current pro ? le selection and control. 15 enb enb enable pin for ldob. active logic high. 16 d4 d4 led4 current channel input. connect to the cathode of backlight led 4. if not used, connect d4 to the out pin. 17 d3 d3 led3 current channel input. connect to the cathode of backlight led 3. if not used, connect d3 to the out pin. 18 gnd gnd ground. 19 ena ena enable pin for ldoa. active logic high. 20 fbb n/c aat2847-ee: feedback pin of ldob. internally regulated at 1.2v. aat2847-qg/qi: no connection. do not make any connection to this pin. ep exposed pad (bottom). pin configuration aat2847-ee aat2847-qg/qi tqfn34-20 tqfn34-20 (top view) (top view) 1 3 2 5 4 6 16 14 15 12 13 11 9 10 7 8 18 17 20 19 d2 d1 ldob in pgnd in fba ldo a c2- c2+ c1+ en/se t c1-out enb d4 d3 gnd ena fbb 1 3 2 5 4 6 16 14 15 12 13 11 9 10 7 8 18 17 20 19 d2 d1 ldob in pgnd in n/c ldo a c2- c2+ c1+ en/setc1- out enb d4 d3 gnd ena n/c downloaded from: http:///
3 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 absolute maximum ratings 1 t a = 25c, unless otherwise noted. pin descriptions below apply to aat2847-ee (aat2847-qg/qi) symbol description value units v n [in, out, d1, d2, d3, d4] to gnd -0.3 to 6.0 v v n [c1+, c1-, c2+, c2-] to gnd -0.3 to v out + 0.3 v v n [ldoa, ldob, fba, fbb, en/set, ena, enb] to gnd -0.3 to v in + 0.3 v t j operating temperature range -40 to 150 c t lead maximum soldering temperature (at leads, 10 sec) 300 c thermal information 2, 3 symbol description value units ja thermal resistance 50 c/w p d maximum power dissipation 2 w 1. stresses above those listed in absolute maximum ratings may cause permanent damage to the device. functional operation at conditions other than the operating conditions specified in not implied. only one absolute maximum rating should be applied at any one time. 2. derate 20mw/c above 40c ambient temperature. 3. mounted on a fr4 circuit board. downloaded from: http:///
4 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 electrical characteristics 1 v in = 3.6v; c in = c ldoa = c ldob = 2.2 f; c out = 1 f; c1 = c2 = 1 f; t a = 25c, unless otherwise noted. typical values are at t a = 25c. symbol description conditions min typ max units power supply v in input voltage range 2.7 5.5 v i shdn total shutdown current at in v en/set = v ena = v enb = 0v 1.0 a charge pump i in input operating current 1x mode, 3.0 ? v in ?? 5.5, active, no load, v ena = v enb = 0v 1.0 ma 1.5x mode, 3.0 ? v in ?? 5.5, active, no load, v ena = v enb = 0v 4.0 2x mode, 3.0 ? v in ?? 5.5, active, no load, v ena = v enb = 0v 5.0 i dx average current accuracy data 1, 20ma range 18 20 22 ma data 2, address 4 0.9 1.0 1.1 data 1, 30ma range 30 data 1, 15ma range 15 i (d-match) current matching 2 v in - v f = 1.5v, 20ma range 0.5 1 % v th 1x to 1.5x or 1.5x to 2x transition threshold at any dx pin 20ma range 150 mv f clk clock frequency 1 mhz t sd over-temperature shutdown threshold 140 c t hys over-temperature shutdown hysteresis 15 c en/set logic control t en/set lo en/set low time 0.3 75 s t en/set_hi_min minimum en/set high time 50 ns t en/set_hi_max maximum en/set high time 75 s t off en/set off timeout 500 s t lat en/set latch timeout 500 s v il(en/set) en/set logic low threshold voltage 0.4 v v ih(en/set) en/set logic high threshold voltage 1.4 v i en/set en/set input leakage v en/set = v in = 5v -1 1 a 1. the aat2847 is guaranteed to meet performance specifications over the C40c to +85c operating temperature range is assured by design, characterization and correlation with statistical process controls. 2. current matching is defined as the deviation of any sink current from the average of all active channels. downloaded from: http:///
5 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 electrical characteristics 1 v in = 3.6v; c in = c ldoa = c ldob = 2.2 f; c out = 1 f; c1 = c2 = 1 f; t a = 25c, unless otherwise noted. typical values are at t a = 25c. symbol description conditions min typ max units ldos: aat2847-ee i in in operating current v ena = v enb = v in , v en/set = 0v, no load 80 150 a v ena = v in ; v enb = 0v; v en/set = 0v; no load 60 112 v fba , v fbb feedback voltage i ldo[a/b] = 1ma to 200ma 1.17 1.2 1.23 v v do dropout voltage i ldo[a/b] = 150ma 150 300 mv ? v out / v out * ? v in line regulation v in = (v ldo[a/b] + 1v) to 5v 0.09 %/v psrr power supply rejection ratio i ldo[a/b] =10ma, 1khz 50 db ldos: aat2847-qg i in in operating current v ena = v enb = v in , v en/set = 0v, no load 80 150 a v ena = v in ; v enb = 0v; v en/set = 0v; no load 60 112 ldoa ldoa voltage tolerance i ldoa = 1ma to 150ma 2.716 2.8 2.884 v ldob ldob voltage tolerance i ldob = 1ma to 150ma 1.455 1.5 1.545 v v do ldoa dropout voltage 2 i ldoa = 150ma 150 300 mv ? v ldo[a/b] / v ldo[a/b] * ? v in ldoa, ldob line regulation v in = (ldoa + 1v) to 5v; v in = (ldob + 1.2v) to 5v 0.09 %/v psrr ldoa, ldob power supply rejection ratio i ldo[a/b] =10ma, 1khz 50 db ldos: aat2847-qi i in in operating current v ena = v enb = v in , v en/set = 0v, no load 80 150 a v ena = v in ; v enb = 0v; v en/set = 0v; no load 60 112 ldoa ldoa voltage tolerance i ldoa = 1ma to 150ma 2.716 2.8 2.884 v ldob ldob voltage tolerance i ldob = 1ma to 150ma 1.746 1.8 1.854 v v do ldoa dropout voltage 2 i ldoa = 150ma 150 300 mv ? v ldo[a/b] / v ldo[a/b] * ? v in ldoa, ldob line regulation v in = (ldo[a/b] + 1v) to 5v 0.09 %/v psrr ldoa, ldob power supply rejection ratio i ldo[a/b] = 10ma, 1khz 50 db ldo logic control C all options v il(ena) , v il(enb) ena, enb input logic low threshold voltage 0.4 v v ih(ena) , v ih(enb) ena, enb input logic high threshold voltage 1.4 v i en[a/b] ena, enb input leakage v en[a/b] = v in = 5v -1 1 a 1. the aat2847 is guaranteed to meet performance specifications over the C40 ? c to +85c operating temperature range is assured by design, characterization and correlation with statistical process controls. 2. v do is defined as v in - ldoa when ldoa is 98% of nominal. downloaded from: http:///
6 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 typical characteristics backlight efficiency vs. input voltage input voltage (v) efficiency (%) 30 40 50 60 70 80 90 100 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 20ma/channel 1ma/channel 14.5ma/channel backlight current matching vs. temperature (i out = 20ma/channel; v in = 4.2v) temperature (c) led current (ma) 18.5 19 19.5 20 20.5 21 -40 -15 10 35 60 85 en/set latch timeout vs. input voltage input voltage (v) t lat (s) 50 100 150 200 250 300 350 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 -40c 85c 25c en/set off timeout vs. input voltage input voltage (v) t off (s) 50 100 150 200 250 300 350 400 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 -40c 85c 25c logic high threshold voltage vs. input voltage input voltage (v) v ih(ena/enb) , v ih(en/set) (v) 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 -40c 25c 85c logic low threshold voltage vs. input voltage input voltage (v) v il(ena/enb) , v il(en/set) (v) 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 -40c 25c 85c downloaded from: http:///
7 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 typical characteristics shutdown current vs. input voltage ( v en/set = v ena/enb = 0v) input voltage (v) shutdown current (na) 0 5 10 15 20 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5. 5 -40c 25c 85c backlight operating characteristic (v in = 3.7v; 1.5x mode; 20ma/channel load; ac coupled) time (500ns/div) v out (40mv/div) v dx (20mv/div) v in (20mv/div) backlight operating characteristic (v in = 3.5v; 1.5x mode; 14ma/channel load; ac coupled) time (500ns/div) v out (40mv/div) v dx (20mv/div) v in (20mv/div) backlight operating characteristic (v in = 2.9v; 2x mode; 20ma/channel load; ac coupled) time (500ns/div) v out (40mv/div) v dx (40mv/div) v in (20mv/div) backlight operating characteristic (v in = 2.9v; 2x mode; 14ma/channel load; ac coupled) time (500ns/div) v out (40mv/div) v dx (40mv/div) v in (20mv/div) downloaded from: http:///
8 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 typical characteristics turn on to 1x mode backlight (20ma/channel; address 0, data 1; v in = 4.2v) time (500ns/div) v out (2v/div) v en/set (2v/div) v dx (500mv/div) i in (100ma/div) turn on to 1.5x mode backlight (20ma/channel; address 0, data 1; v in = 3.5v) time (200s/div) v out (2v/div) v en/set (2v/div) v dx (500mv/div) i in (200ma/div) turn on to 2x mode backlight (20ma/channel; address 0, data 1; v in = 3.2v) time (200s/div) v out (2v/div) v en/set (2v/div) v dx (500mv/div) i in (200ma/div) turn off from 1.5x mode backlight (20ma/channel; address 0, data 1; v in = 3.6v ) time (100s/div) v out (2v/div) v en/set (2v/div) i led (20ma/div) ldoa/ldob load regulation load current (ma) output voltage error (%) -1.0 -0.5 0.0 0.5 1.0 0.1 1 10 100 1000 ldoa ldob ldoa/ldob line regulation input voltage (v) output voltage error (%) -1.000 -0.500 0.000 0.500 1.000 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 ldoa ldob downloaded from: http:///
9 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 typical characteristics ldoa/ldob quiescent current vs. input voltage (v out = 1.2v) input voltage (v) quiescent current (a) 0 20 40 60 80 100 120 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 85c 25c -40c ldoa load transient response (v in = 3.6v; v ldoa = 1.2v) time (20s/div) v ldoa (100mv/div) i ldoa (100ma/div) 200ma 10ma ldob load transient response (v in = 3.6v; v ldob = 1.2v) time (20s/div) v ldob (100mv/div) i ldob (100ma/div) 200ma 10ma ldoa line transient response (10ma load) time (40s/div) v ldoa (20mv/div) v in (400mv/div) v in = 4.2v v in = 3.6v ldob line transient response (10ma load) time (40s/div) v ldob (20mv/div) v in (400mv/div) v in = 3.6v v in = 4.2v downloaded from: http:///
10 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 typical characteristics ldoa/ldob turn on (v in = 3.6v; v ldo(a/b) = 2.8v; dc coupled) time (40s/div) v ldo(a/b) (1v/div) v en(a/b) (2v/div) ldoa/ldob turn on (v in = 3.6v; v ldo(a/b) = 1.8v; dc coupled) time (40s/div) v ldo(a/b) (1v/div) v en(a/b) (2v/div) ldoa/ldob turn on (v in = 3.6v; v ldo(a/b) = 1.5v; dc coupled) time (40s/div) v ldo(a/b) (500mv/div) v en(a/b) (2v/div) ldoa/ldob turn on (v in = 3.6v; v ldo(a/b) = 1.2v; dc coupled) time (40s/div) v ldo(a/b) (500mv/div) v en(a/b) (2v/div) downloaded from: http:///
11 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 functional description the aat2847 is an integrated solution for lcd display applications with a built-in four channel white led driver (charge pump) and dual 200ma ldo voltage regulators. the aat2847 incorporates a tri-mode charge pump with load switch (1x) functionality and high efficiency (1.5x or 2x) performance. to maximize power conversion effi- ciency, an internal sensing circuit monitors the voltage required at each white led cathode input pin (d1-d4) and sets the load switch and charge pump mode based on the input battery voltage and the white led cathode pin voltage. the voltage threshold for 1x to 1.5x and 1.5x to 2x mode transitions is v th . the charge pump in the aat2847 starts-up in 1x mode (default); under this condition, if the led cathode input pin voltage is below v th the aat2847 will transition into 1.5x mode. when 1.5x mode does not provide enough current through the white leds for backlight applica- tions, which occurs during the normal discharge of the input battery power source, the led cathode input pin voltage will drop below v th and the aat2847 will transi- tion into 2x mode. the charge pump requires only four external capacitors, 1 f ceramic capacitors for the flying (c1 and c2), input (c in ), and output (c out ) capacitors. the four led cathode input pins (d1-d4) can drive indi- vidual leds with a maximum current of 30ma each. the unused led cathode input pins have to be connected to the out pin, otherwise the aat2847 will operate in 2x mode only. operating in 2x mode when it is not neces- sary will result in a significant reduction in efficiency. the as2cwire serial interface enables the charge pump and sets the current flowing into the led cathode input pins. the aat2847 also contains dual ldo voltage regulators that have separate enable pins from each other and the charge pump. the separate enable pins for each dc/dc device in the aat2847 allow for every possible device operational combination. the two ldo regulators require 2.2 f output capacitors for stable operation. functional block diagram tri-mode (1x, 1.5x and 2x) charge pump d/a d/a d/a d/a 6 x16 bit rom as 2 cwire interface 1mhz oscillator voltage reference in en/set gnd d4 d3 d2 d1 out c1+ c1- c2+ c2- ldo a in ldoa (2.8v/2.8v) fba (nc) ldo b ldob (1.5v/1.8v) fbb (nc) ena 1.2v reference aat 2847-ee (aat 2847-qg/-qi) (aat 2847-qg/-qi) pgnd enb downloaded from: http:///
12 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 0.0 5.0 10.0 15.0 20.0 25.0 30.0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 2 3 4 code led current (ma) address 0 address 4 figure 1: led current control profile. as 2 cwire serial interface each white led channel input on the aat2847 (d1-d4) is controlled by skyworks' as 2 cwire serial digital interface. the as 2 cwire interface uses the number of rising edges on the en/set pin to address and load the led configura- tion registers. as 2 cwire latches data or addresses after the en/set pin has been held logic high for longer than t lat (500 s). addresses and data are differentiated by the number of en/set rising edges. since the data reg-isters are 4 bits each, the differentiating number of pulses is 24 or 16, so that address 0 is signified by 17 rising edges, address 1 by 18 rising edges, address 2 by 19 rising edges, and so on. data is set to any number of rising edges between, and including, 1 to 16. a typical write protocol consist of the following: first a burst of en/set rising edges that identify/target a par- ticular address followed by en/set being held logic high for the t lat timeout period to latch the address value in the address register, then another burst of rising edges that signify data with the accompanying t lat timeout period to latch the data value in the data register. once an address is set, then multiple writes to the correspond- ing data register are allowed without having to write to the address for every value change in the data register. when en/set is held low longer than t off (500 s), the aat2847 enters shutdown mode operation and draws less than 1 a from the input supply voltage. data and address registers are cleared (0 for the address register and 1 for the data registers) in shutdown mode operation. as 2 cwire serial interface addressing address en/set edges addressed register 0 17 d1-d4 current control 3 20 current scale 4 21 low current control 5 22 independent led control table 1: as 2 cwire serial interface addressing. current operation (address 0) use address 0 to program all four led channels with the current values in table 2. all four white led channels are programmed to the same current level by writing to address 0 followed by any data between, and including, 1 to 16. current scale (address 3) the aat2847 has three selectable current scales for the four white led channels: 30ma, 20ma, and 15ma. only one of the three current scales can be active at any given time. by default, the 20ma current scale is active upon start-up. to change to the 30ma or 15ma current scale, or go back to the 20ma scale, write to address 3 with the appropriate data between, and including, 1 to 3. to enable low current mode, write data 4 to address 3. low current mode results in the four white led channels reverting to the current set by the low current settings in address 4. data 30ma scale 20ma scale 15ma scale 1 30.0 20.0 15.0 2 28.5 19.0 14.3 3 26.6 17.7 13.3 4 25.2 16.8 12.6 5 23.3 15.5 11.6 6 21.8 14.5 10.9 7 19.8 13.2 9.9 8 18.5 12.3 9.2 9 16.5 11.0 8.3 10 15.0 10.0 7.5 11 13.1 8.7 6.5 12 11.6 7.7 5.8 13 9.8 6.5 4.9 14 8.3 5.5 4.1 15 6.3 4.2 3.2 16 4.8 3.2 2.4 table 2: current settingsaddress 0. downloaded from: http:///
13 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 data current scale 1 20ma scale 2 30ma scale 3 15ma scale 4 low current mode table 3: current scale settingsaddress 3. low current operation (address 4) all four led channels are programmed to the same low current level by writing to address 4 followed by any data between, and including, 1 to 4. this operational mode is especially useful for low current applications where a continuous low current state is maintained for a substantial length of time. data ma 1 0.5 2 1.0 3 1.5 4 2.0 table 4: low current settingsaddress 4. independent led current control (address 5) independent led control allows for individual leds to be enabled and disabled to form custom arrangement of active leds. to enable independent control write address 5 with data between, and including, 1 to 16. data d4 d3 d2 d1 1 o no no no n 2 o no no no f f 3 on on off on 4 on on off off 5 on off on on 6 on off on off 7 on off off on 8 on off off off 9 off on on on 10 off on on off 11 off on off on 12 off on off off 13 off off on on 14 off off on off 15 off off off on 16 off off off off table 5: independent led control settings address 5. address data 1 en/set 2 19 20 a ddress data 3 data 0 1 2 . . . n 16 03 11 n t hi t lo t lat t lat figure 2: as 2 cwire serial interface timing. downloaded from: http:///
14 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 auto disable feature the charge pump in the aat2847 is equipped with an auto-disable feature for each led channel. after the ic is enabled and successively starts-up, a test current of 100 a (typical) is forced through each led channel. the channel will be disabled if the voltage on that particular dx pin does not drop to certain threshold. this feature is convenient for disabling an unused channel or during an led short circuiting event. low dropout regulators the aat2847 incorporates two ldo voltage regulators. the two regulators run from the same 2.7v to 5.5v input voltage as the charge pump and have separate on/off control inputs, ena and enb. for the aat2847-ee, the ldo output voltages are set through a resistive voltage divider from the output (ldoa or ldob) to the feedback input (fba or fbb). the ratio of the voltage divider resis- tor values determines the ldo output voltage. for the aat2847-qg option, ldoa is internally set to 2.8v and ldob is internally set to 1.5v. for the aat2847-qi option, ldoa is also 2.8v and ldob is internally set to 1.8v. each ldo regulator can supply a continuous load current up to 200ma, and both ldos include current limiting and thermal overload protection to prevent dam- age to the load or to the ldo. thermal protection the charge pump has built-in thermal protection cir- cuitry that will shut down the charge pump and the ldos if the die temperature rises above the thermal limit, as is the case during an out pin short circuit event. applications informationled selection the charge pump in the aat2847 is specifically intended for driving white leds. however, the aat2847 can drive most types of leds with forward voltage specifications ranging from 2.0v to 4.7v. led applications may include mixed arrangements for display backlighting, color (rgb) leds, infrared (ir) diodes and any other load needing a constant current source generated from a varying input voltage. since the d1 to d4 constant current channels are matched with negligible voltage dependence, the constant current channels will be matched regardless of the specific led forward voltage (v f ) levels. multiple channels can be combined to obtain a higher led drive current without complication. aat2847-ee ldo outputvoltage programming the output voltages for ldoa and ldob are programmed by an external resistor divider network. as shown in figure 3, the selection of r1 and r2 is a straightforward matter. r1 is chosen by considering the tradeoff between the feedback network bias current and resistor value. higher resistor values allow stray capacitance to become a larger factor in circuit performance, whereas lower resistor values decrease efficiency. v ldo(a/b) r2(a/b) v ref = 1.2v r1(a/b) ldo(a/b) fb(a/b) figure 3: selection of external resistors. to select appropriate resistor values, first choose a value for r1 that will produce a reasonable feedback network bias current. then, according to the desired v ldo(a/b) , cal- culate r2 according to the equation below. an example calculation follows. r1 is chosen to be 120k , resulting in a small feedback network bias current of 10 a (v fb(a/b) /r1 = 1.2v/120k ). the desired output voltage is 1.8v. from this informa- tion, r2 is calculated from the equation below: downloaded from: http:///
15 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 r2 (a/b) = r1 (a/b) (v ldo(a/b) - 1.2v) 1.2v the result is r2 = 60k . since 60k is not a standard 1% resistor value, 60.4k is selected. from this exam- ple calculation, for v out = 1.8v, use r1 = 120k and r2 = 60.4k . a table of example output voltages and cor- responding resistor values is provided below. r2 standard 1% values (r1 = 120k ) v ldo(a/b) (v) r2 ( ) 2.8 160k 2.5 130k 2 79.6k 1.8 60.4k 1.5 30.1k table 6: example output voltages and corresponding resistor values. device power efficiency the aat2847s charge pump conversion efficiency is defined as the power delivered to the white led load divided by the input power: = = p leds p in v led1 i led1 + ... + v led4 i led4 v in i in v ledx = white led forward voltage (v f ) i ledx = white led bias current (i d ) the expression to define the estimated ideal efficiency ( ) for the aat2847 in 1x mode is as follows: = = p leds p in v led1 i led1 + ... + v led4 i led4 v in i in = ; x = 1, 2, 3 or 4 and i in = 4 i ledx = 4 v ledx i ledx v in i in v ledx v in the aat2847s charge pump is a fractional charge pump which will boost the input supply voltage in the event where v in is less then the required output voltage across the white led load. the efficiency can be simply defined as a linear voltage regulator with an effective white led forward voltage that is equal to one and a half (1.5x mode) or two (2x mode) times the input voltage. with an ideal 1.5x charge pump, the input current is 1.5x of the output current. the expression to define the estimated ideal efficiency ( ) for the aat2847 in 1.5x mode is as follows: = = p leds p in v led1 i led1 + ... + v led4 i led4 v in i in = ; x = 1, 2, 3 or 4 and i in = 1.5(4 i ledx ) = 4 v ledx i ledx v in i in v ledx 1.5v in the same calculations apply for the aat2847 in 2x mode where for an ideal 2x charge pump, the input current is 2x of the output current. the expression for the esti- mated ideal efficiency ( ) for the aat2847 in 2x mode is as follows: = = p leds p in v led1 i led1 + ... + v led4 i led4 v in i in = ; x = 1, 2, 3 or 4 and i in = 2(4 i ledx ) = 4 v ledx i ledx v in i in v ledx 2v in capacitor selectioncareful selection of the six external capacitors c in , c1, c2, c ldoa , c ldob , and c out are important because they will affect turn on time, output ripple and transient perfor- mance. optimum performance will be obtained when low esr (<100m ) ceramic capacitors are used. in general, low esr is defined as a resistance that is less than 100m . x7r and x5r type ceramic capacitors are highly recom- mended over all other types of capacitors for use with the aat2847. for the charge pump section, a 1 f or greater capacitor is required for the fly (c1 and c2) and output (c out ) capacitors. the dual ldos require a 2.2 f or greater output capacitor. the required input capacitor (c in ) is 2.2 f or greater. ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counterparts. a ceramic capacitor typically has very low esr, is lowest cost, has a smaller printed circuit board (pcb) footprint, and is non-polarized. low esr ceramic capacitors maxi- mize charge pump transient response. downloaded from: http:///
16 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 before choosing a particular capacitor, verify the capaci- tors performance with the characteristics illustrated in the components data sheet. performance verification will help avoid undesirable component related perfor- mance deficiencies. pcb layout to achieve adequate electrical and thermal performance, careful attention must be given to the pcb layout. in the worst-case operating condition, the chip must dissipate considerable power at full load. adequate heat-sinking must be achieved to ensure intended operation. figures 5 and 6 illustrate an example pcb layout. the bottom of the package features an exposed metal pad. the exposed pad acts, thermally, to transfer heat from the chip and, electrically, as a ground connection. the junction-to-ambient thermal resistance ( ja ) for the connection can be significantly reduced by following a couple of important pcb design guidelines. the pcb area directly underneath the package should be plated so that the exposed paddle can be mated to the top layer pcb copper during the reflow process. multiple copper plated thru-holes should be used to electrically and thermally connect the top surface pad area to additional ground plane(s). the chip ground is internally connected to both the exposed pad and to the agnd and pgnd pins. it is good practice to connect the gnd pins to the exposed pad area with traces as shown in figure 4. the flying capacitors (c1 and c2), input capacitor (c4), and output capacitors (c3, c5, and c6) should be con- nected as close as possible to the ic. in addition to the external passive components being placed as close as possible to the ic, all traces connecting the aat2847 should be as short and wide as possible to minimize path resistance and potential coupling. pin #1 figure 4: aat2847 package layout. downloaded from: http:///
17 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 evaluation board layout figure 5: aat2847 evaluation board figure 6: aat2847 evaluation board component side layout. solder side layout. evaluation board schematic c1 c2 c3 c4 d1 d2 d3 d4 c5 r8 r9 c6 r10 r11 dc+ 1 2 3 j1 d2 1 fbb 20 d1 2 ldob 3 in 4 pgnd 5 in 6 fba 7 l doa 8 c2- 9 c2+ 10 out 11 c1- 12 c1+ 13 en/set 14 enb 15 d4 16 d3 17 gnd 18 ena 19 u1aat2847 dc+ 1 2 3 j2 dc+ 1 2 3 j3 r12 r13 r14 en/set ldob ldoa figure 7: aat2847 section schematic. downloaded from: http:///
18 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 vdd 1 gp5 2 gp4 3 gp3 4 gp2 5 gp1 6 gp0 7 vss 8 pic12f675 u2 c8 r5 red led7 1 2 3 j4 r7 r6 data light sw dc+ dc+ r1 r2 r3 en/set figure 8: mcu section schematic. downloaded from: http:///
19 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 ordering information package low dropout regulators marking 1 part number (tape and reel) 2 ldoa ldob tqfn34-20 programmable programmable ylxxy AAT2847IML-EE-T1 tqfn34-20 2.8v 1.5v aat2847iml-qg-t1 tqfn34-20 2.8v 1.8v zdxyy aat2847iml-qi-t1 skyworks green? products are compliant with all applicable legislation and are halogen-free. for additional information, refer to skyworks de?ition of green , document number sq04-0074. 1. xyy = assembly and date code. 2. sample stock is generally held on part numbers listed in bold . downloaded from: http:///
20 aat2847 data sheet four-channel backlight driver with dual ldos skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 202068a skyworks proprietary information products and product information are subject to change without notice. june 15, 2012 copyright ? 2012 skyworks solutions, inc. all rights reserved. information in this document is provided in connection with skyworks solutions, inc. (skyworks) products or services. these materials, including the information contained herein, are provided by sky works as a service to its customers and may be used for informational purposes only by the customer. skyworks assumes no responsibility fo r errors or omissions in these materials or the information contained herein. sky- works may change its documentation, products, services, speci ? cations or product descriptions at any time, without notice. skyworks makes no commitment to update the materials or information and shall have no responsibility whatsoever for con ? icts, incompatibilities, or other dif ? culties arising from any future changes. no license, whether express, implied, by estoppel or otherwise, is granted to any intellectual property rights by this document. skyworks assumes no liability for any materials, products or informatio n provided here- under, including the sale, distribution, reproduction or use of skyworks products, information or materials, except as may be provided in skyworks terms and conditions of sale. the materials, products and information are provided as is without warranty of any kind, whether express, implied, statutory, or otherwise, including fitness for a particular purpose or use, merchantability, performance, quality or non-infringement of any intellectual property right; all such warranti es are hereby expressly disclaimed. skyworks does not warrant the accuracy or completeness of the information, text, graphics or other items contained within these materials. skyworks shall not be liable for any damages, in- cluding but not limited to any special, indirect, incidental, statutory, or consequential damages, including without limitation, lost revenues or lost profits that may result from the use of the materials or information, whether or not the recipient of materials has been advised of the possibility of such damage. skyworks products are not intended for use in medical, lifesaving or life-sustaining applications, or other equipment in which the failure of the skyworks products could lead to personal injury, death, physical or en- vironmental damage. skyworks customers using or selling skyworks products for use in such applications do so at their own risk and agree to fully indemnify skyworks for any damages resulting from such improper use or sale. customers are responsible for their products and applications using skyworks products, which may deviate from published speci ? cations as a result of design defects, errors, or operation of products outside of pub- lished parameters or design speci ? cations. customers should include design and operating safeguards to minimize these and other risks. skyworks assumes no liabi lity for applications assistance, customer product design, or damage to any equipment resulting from the use of skyworks products outside of stated published speci ? cations or parameters. skyworks, the skyworks symbol, and breakthrough simplicity are trademarks or registered trademarks of skyworks solutions, inc., in the united states and other countries. third-party brands and names are for identi ? cation purposes only, and are the property of their respective owners. additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference. package information 1 tqfn34-20 top view side view detail "a" bottom view 3.00 0.05 1.55 0.05 0.40 0.100 detail "a" 4.00 0.05 0.025 0.025 0.75 0.05 0.214 0.036 2.55 0.05 0.50 bsc 0.24 0.060 all dimensions in millimeters. 1. the leadless package family, which includes qfn, tqfn, dfn, tdfn, and stdfn, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. a solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder c onnection. downloaded from: http:///

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