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aat2845a four-channel backlight driver with dual ldos 2845a.2007.05.1.0 1 chargepump ? general description the aat2845a is a highly integrated power solu- tion for single-cell lithium-ion-based lcd display applications. it includes a four-channel led back- light driver and two integrated 200ma ldos as additional power supplies for display and camera- related chipsets. the backlight driver is a low noise, constant fre- quency charge pump dc/dc converter that uses a tri-mode load switch (1x), fractional (1.5x), and doubling (2x) conversion to maximize efficiency. each of the four channels is capable of driving up to 20ma per channel. analogictech's s 2 cwire? (simple serial control?) serial digital input is used to enable, disable, and set current for each led with 16 available settings down to 50a. the low current mode supply current can be as low as 50a to save power and maintain high efficiency. each led output is equipped with built-in protec- tion for short-circuit and auto-disable functions. built-in soft-start circuitry prevents excessive inrush current during start-up. a low current shut- down feature disconnects the load from v in and reduces quiescent current to less than 1a. the aat2845a is available in a pb-free, thermally- enhanced 20-pin 3x4mm tqfn package. features ? input voltage range: 2.7v to 5.5v ? four-channel led driver: tri-mode charge pump up to 20ma/channel easy control with single wire interface 16 current levels four low current settings down to 50a low i q (50a) for low current mode >90% peak efficiency ? dual 200ma ldos ? automatic soft-start ? over-temperature protection ? available in 3x4mm 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 d1 d2 d3 d4 200ma ldoa aat2845a gnd en/set s 2 cwire backlight control co 1 c out 1f c in 2.2f v bat 3.6v 200ma ldob co 2 enldo ldo enable cbp in fba fbb c byp 0.1f
aat2845a four-channel backlight driver with dual ldos 2 2845a.2007.05.1.0 pin descriptions pin configuration tqfn34-20 (top view) pin # symbol function 1 d2 current sink input #2. 2 d1 current sink input #1. 3 ldob output of ldo b. connect a 2.2f or larger ceramic capacitor to ground. 4 in input power supply for charge pump. requires a 1f or larger ceramic capacitor connected between this pin and ground. 5 pgnd power ground. 6 in input power pin for both ldos. connect a 1f or larger ceramic capacitor from this pin to pgnd. 7 fba feedback pin of ldo a. regulated at 1.2v. 8 ldoa output of ldo a. connect a 2.2f or larger ceramic capacitor to ground. 9 c2- flying capacitor 2 negative terminal. 10 c2+ flying capacitor 2 positive terminal. connect a 1f ceramic capacitor between c2+ and c2-. 11 out charge pump output to drive load circuit. connect a 1f or larger ceramic capacitor between this pin and pgnd. 12 c1- flying capacitor 1 negative terminal. 13 c1+ flying capacitor 1 positive terminal. connect a 1f ceramic capacitor between c1+ and c1-. 14 en/set s 2 cwire control pin for backlighting. 15 enldo enable pin for ldo a and b. 16 d4 current sink input #4. 17 d3 current sink input #3. 18 gnd ground. 19 cbp bypass pin for the internal reference. connect a 0.1f ceramic capacitor from this pin to gnd. 20 fbb feedback pin of ldo b. regulated at 1.2v. ep exposed paddle (bottom); connect to pgnd as closely as possible to the device. 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/set c1- out enldo d4 d3 gnd cbp fbb
aat2845a four-channel backlight driver with dual ldos 2845a.2007.05.1.0 3 absolute maximum ratings 1 t a = 25c, unless otherwise noted. thermal information 2, 3, 4 symbol description value units ja thermal resistance 50 c/w p d maximum power dissipation 2 w symbol description value units in, out, d1,d2, d3, d4 voltage to gnd -0.3 to 6.0 v c1+, c1-, c2+, c2- voltage to gnd -0.3 to v out +0.3 v ldoa, ldob, fba, fbb, en/set, enldo, cbp -0.3 to v in +0.3 v voltage to gnd pgnd voltage to gnd -0.3 to +0.3 v t j operating temperature range -40 to 150 c t lead maximum soldering temperature (at leads, 10 sec) 300 c 1. stresses above those listed in absolute maximum ratings may cause permanent damage to the device. functional operation at co ndi- tions other than the operating conditions specified is not implied. only one absolute maximum rating should be applied at any one time. 2. based on long-term current density limitation. 3. derate 20mw/ c above 40 c a mbient temperature. 4. mounted on an fr4 circuit board.
aat2845a four-channel backlight driver with dual ldos 4 2845a.2007.05.1.0 electrical characteristics 1 c in = c o1 = c o2 = 2.2f, c 1 = c 2 = 1.0f, c bp = 0.1f; t a = 25c, unless otherwise noted. typical values are at t a = 25c and v in = 3.6v. symbol description conditions min typ max units power supply v in supply voltage 2.7 5.5 v i shdn total shutdown current at vin en/set = enldo = gnd 1.0 a and ldoin charge pump 1x mode, 3.0 v in 5.5, 1.0 active, no load current 1.5x mode, 3.0 v in 5.5, 3.0 ma i cc operating current active, no load current 2x mode, 3.0 v in 5.5, 5.0 active, no load current 50a setting, 1x mode 50 a 20ma setting, t a = 25c 18 20 22 i dx average current accuracy 1ma setting, t a = 25c 0.9 1.0 1.1 ma i (d-match) current matching 2 v in - v f = 1.5v 0.5 1.0 % v th 1x to 1.5x or 1.5x to 2x transition 20ma setting, t a = 25c 150 mv threshold at any dx pin t ss soft-start time 100 s f clk clock frequency 1 mhz t sd over-temperature shutdown 140 c threshold t hys over-temperature shutdown 15 c hysteresis 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 i en/set en/set input leakage v en/set = v in = 5v -1 1 a 1. the aat2845a is guaranteed to meet performance specifications over the -40c to +85c operating temperature range and is ass ured 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.
aat2845a four-channel backlight driver with dual ldos 2845a.2007.05.1.0 5 electrical characteristics 1 c in = c o1 = c o2 = 2.2f, c 1 = c 2 = 1.0f, c bp = 0.1f; t a = 25c, unless otherwise noted. typical values are at t a = 25c and v in = 3.6v. symbol description conditions min typ max units ldos i in in operating current enldo = in, en/set = agnd, 80 150 a no load v fb feedback voltage i out = 1ma to 200ma 1.17 1.2 1.23 v v do dropout voltage i out = 150ma 150 300 mv v out / line regulation v in = (v out + 1v) to 5.0v 0.09 %/v v out * v in psrr power supply rejection ratio i out =10ma, 1khz 50 db ldo logic control v il en/set, enldo pins logic 0.4 v low threshold v ih en/set, enldo pins logic high 1.4 v threshold 1. the aat2845a is guaranteed to meet performance specifications over the -40c to +85c operating temperature range and is ass ured by design, characterization, and correlation with statistical process controls.
typical characteristics c in = c o1 = c o2 = 2.2f, c 1 = c 2 = 1.0f, c bp = 0.1f; t a = 25c, unless otherwise noted. typical values are at t a = 25c and v in = 3.6v. aat2845a four-channel backlight driver with dual ldos 6 2845a.2007.05.1.0 turn-off from 1.5x mode backlight time (100s/div) v f (2v/div) en/set (2v/div) i in (200ma/div) turn-on to 1.5x mode (v in = 3.5v; 20ma/ch load) time (100s/div) v out (2v/div) v sink (1v/div) en/set (2v/div) i in (200ma/div) turn-on to 2x mode (v in = 2.8v; 20ma/ch load) time (100s/div) v out (2v/div) v sink (500mv/div) en/set (2v/div) i in (500ma/div) backlight efficiency vs. supply voltage supply voltage (v) efficiency (%) 30 40 50 60 70 80 90 100 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 1ma/ch 15.2ma/ch 20ma/ch turn-on to 1x mode (v in = 4.2v; 20ma/ch load) time (100s/div) v out (2v/div) v sink (1v/div) en/set (2v/div) i in (100ma/div)
typical characteristics c in = c o1 = c o2 = 2.2f, c 1 = c 2 = 1.0f, c bp = 0.1f; t a = 25c, unless otherwise noted. typical values are at t a = 25c and v in = 3.6v. aat2845a four-channel backlight driver with dual ldos 2845a.2007.05.1.0 7 en/set latch timeout vs. supply voltage supply voltage (v) en/set latch timeout (s) 0 50 100 150 200 250 300 350 400 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 85 c 25 c -40 c en/set off timeout vs. supply voltage supply voltage (v) en/set off timeout (s) 0 50 100 150 200 250 300 350 400 450 500 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 85 c 25 c -40 c backlight operating characteristic (v in = 3.5v; 1.5x mode; 13.5ma/ch load) time (500ns/div) v in (20mv/div) v sink (20mv/div) v out (40mv/div) backlight operating characteristic (v in = 3.7v; 1.5x mode; 20ma/ch load) time (500ns/div) v in (20mv/div) v out (40mv/div) v sink (20mv/div) backlight operating characteristic (v in = 2.9v; 2x mode; 13.5ma/ch load) time (500ns/div) v in (20mv/div) v sink (40mv/div) v out (40mv/div) backlight operating characteristic (v in = 2.9v; 2x mode; 20ma/ch load) time (500ns/div) v in (20mv/div) v out (40mv/div) v sink (40mv/div)
typical characteristics c in = c o1 = c o2 = 2.2f, c 1 = c 2 = 1.0f, c bp = 0.1f; t a = 25c, unless otherwise noted. typical values are at t a = 25c and v in = 3.6v. aat2845a four-channel backlight driver with dual ldos 8 2845a.2007.05.1.0 ldos a and b line regulation (10ma load) supply voltage (v) error (%) -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 outa outb en/set low threshold voltage vs. supply voltage supply voltage (v) en/set low threshold voltage (v) 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 85 c 25 c -40 c en/set high threshold voltage vs. supply voltage supply voltage (v) en/set high threshold voltage (v) 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 85 c 25 c -40 c ldos a and b load regulation (v out = 1.2v) load current (ma) error (%) -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 0.1 1 10 100 100 outa outb ldos a and b line transient response (v out = 2.5v; 10ma load) time (40s/div) v out (10mv/div) v in (400mv/div) v in = 3.7v v in = 4.2v ldos a and b turn-on characteristic time (50s/div) v out (500mv/div) enldo (2v/div)
typical characteristics c in = c o1 = c o2 = 2.2f, c 1 = c 2 = 1.0f, c bp = 0.1f; t a = 25c, unless otherwise noted. typical values are at t a = 25c and v in = 3.6v. aat2845a four-channel backlight driver with dual ldos 2845a.2007.05.1.0 9 ldos a and b load transient response (v out = 2.5v) time (20s/div) v out (100mv/div) i out (100ma/div)
aat2845a four-channel backlight driver with dual ldos 10 2845a.2007.05.1.0 functional block diagram functional description the aat2845a is an integrated solution for lcd display applications with a built-in driver for white led backlight and two ldo voltage regulators for logic power supplies. the backlight driver is a tri-mode load switch (1x) and high-efficiency (1.5x or 2x) charge pump device. to maximize power conversion efficiency, an internal sensing circuit monitors the voltage required on each constant current sink input and sets the load switch and charge pump modes based on the input battery voltage and the current sink input voltage. as the battery discharges over time, the charge pump is enabled when any of the four current sink inputs nears dropout. the charge pump initially starts in 1.5x mode. if the charge pump output droops enough for any current source output to become close to dropout, the charge pump will automatically transition to 2x mode. the charge pump requires only four external compo- nents: two 1f ceramic capacitors for the charge pump flying capacitors (c 1 and c 2 ), one 1f ceramic input capacitor (c in ), and one 0.33f to 1f ceramic charge pump output capacitor (c out ). the four constant current sink inputs (d1 to d4) can drive four individual leds with a maximum cur- rent of 20ma each. the unused sink inputs must be connected to the out pin; otherwise the part will operate only in 2x charge pump mode. the s 2 cwire serial interface enables the charge pump and sets the current sink magnitudes. constant current output level settings the constant current sink levels for d1 to d4 are set via the s 2 cwire serial interface according to a logarithmic scale for the first 12 codes, and a sep- arate low-current scale for the last four codes. because the inputs d1 to d4 are true independent constant current sinks, the voltage observed on any single given input will be determined by the dif- ference between v out and the actual forward volt- age (v f ) of the led being driven. since the current level is programmable, no pwm (pulse width modulation) or additional control cir- tri-mode (1x, 1.5x and 2x) charge pump d/a d/a d/a d/a 6x16 bit rom s 2 cwire interface soft-start control 1mhz oscillator voltage reference in en/set gnd d4 d3 d2 d1 out c1+ c1- c2+ c2- ldo a in ldo a fba ldo b ldob fbb enldo cbp 1.2v reference
aat2845a four-channel backlight driver with dual ldos 2845a.2007.05.1.0 11 cuitry is needed to control led brightness. this feature greatly reduces the burden on a microcon- troller or system ic to manage led or display brightness, allowing the user to "set it and forget it." with its high-speed serial interface (>1mhz data rate), the led current drive can be changed suc- cessively to brighten or dim leds in smooth transi- tions (e.g., to fade out) or in abrupt steps, giving the user complete programmability and real-time con- trol of led brightness. the last four codes of the current level scale engage a reduced quiescent current mode that enhances the low-current setting efficiency. this mode is especially useful for low-current applica- tions where a continuous, low-current state is maintained for a substantial length of time. s 2 cwire serial interface the current sink magnitude is controlled by analogictech's s 2 cwire serial digital input. the interface records rising edges of the en/set pin and decodes them into 16 different states. the 16 current level settings available are indicated in table 1. table 1: current level settings. the s 2 cwire serial interface has flexible timing. data can be clocked-in at speeds higher than 1mhz, or much slower, such as 15khz. after data is applied, en/set is held high to latch the data. once en/set has been held in the logic high state for time t lat (500s), the programmed current becomes active and the internal data register is reset to zero. for subsequent current level pro- gramming, the number of rising edges correspon- ding to the desired code must be applied on the en/set pin. when the en/set pin is held low for an amount of time longer than t off (500s), the aat2845a enters shutdown mode and draws less than 1a from the input. an internal data register is reset to zero during shutdown. auto-disable feature the charge pump in the aat2845a is equipped with an auto-disable feature for each led channel. after the ic is enabled and started up, a test cur- rent of 100a (typical) is forced through each sink channel. the channel will be disabled if the voltage of that particular dx pin does not drop to a certain threshold. this feature is convenient for disabling an unused channel or during an led fail-short event. low dropout regulators the aat2845a includes two ldo linear regulators. the regulators run from the same 2.7v to 5.5v input voltage as the charge pump. the regulators use a single on/off control input, enldo. the ldo output voltages are set through a resistive voltage divider from the output (outa or outb) to the feedback input (fba or fbb). the ratio of resistor values determines the ldo output voltage. the low 200mv dropout voltage at 200ma load current allows the regulator to maintain output voltage regulation. each ldo regulator can supply a continuous load current up to 200ma. both ldos include current limiting and thermal overload protection to prevent damage to the load or to the ldos. thermal protection the charge pump has a built-in thermal protection circuit that will shut down the charge pump and the ldos if the die temperature rises above the ther- mal limit, as is the case during a short-circuit of the out pin. output output data (ma/ch) data (ma/ch) 1 20 9 6.8 2 18.4 10 5.2 3 16.8 11 3.5 4 15.2 12 2.0 5 13.5 13 1.0 6 11.9 14 0.5 7 10 15 0.10 8 8.4 16 0.05
aat2845a four-channel backlight driver with dual ldos 12 2845a.2007.05.1.0 applications information led selection the aat2845a is specifically intended for driving white leds. however, the device design will allow the aat2845a to drive most types of leds with for- ward voltage specifications ranging from 2.0v to 4.7v. led applications may include mixed arrange- ments 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 sinks are matched with negligible voltage depend- ence, the constant current channels will be matched regardless of the specific led forward voltage (v f ) levels. the low dropout current sinks in the aat2845a maximize performance and make it capable of driv- ing leds with high forward voltages. multiple chan- nels can be combined to obtain a higher led drive current without complication. device switching noise performance the aat2845a operates at a fixed frequency of approximately 1mhz to control noise and limit har- monics that can interfere with the rf operation of cellular telephone handsets or other communica- tion devices. back-injected noise appearing on the input pin of the charge pump is 20mv peak-to- peak, typically ten times less than inductor-based dc/dc boost converter white led backlight solu- tions. the aat2845a soft-start feature prevents noise transient effects associated with inrush cur- rents during start-up of the charge pump circuit. shutdown since the sink switches are the only power returns for all loads, there is no leakage current when all of the sink switches are disabled. to activate the shut- down mode, hold the en/set input low for longer than t off (500s). in this state, the aat2845a typ- ically draws less than 1a from the input. data and address registers are reset to 0 in shutdown. ldo output voltage programming the output voltages for ldoa and ldob are pro- grammed by an external resistor divider network. as shown below, the selection of r8 and r9 is a straightforward matter. r9 is chosen by considering the tradeoff between the feedback network bias current and resistor value. higher resistor values allow stray capaci- tance to become a larger factor in circuit perform- ance, whereas lower resistor values increase bias current and decrease efficiency. figure 2: selection of external resistors. figure 1: s 2 cwire serial interface timing. r 8 (r10) r 9 (r11) v out outa (outb) fba (fbb) v ref = 1.2v 1 en/set 2 n-1 n 16 data reg 0 n-1 0 t hi t lo t lat t off
aat2845a four-channel backlight driver with dual ldos 2845a.2007.05.1.0 13 to select appropriate resistor values, first choose r9 such that the feedback network bias current is reasonable. then, according to the desired v out , calculate r8 according to the equation below. an example calculation follows. r9 is chosen to be 120k, resulting in a small feed- back network bias current of 1.2v/120k = 10a. the desired output voltage is 1.8v. from this infor- mation, r8 is calculated from the equation below. the result is r8 = 60k. since 60k is not a standard 1% value, 60.4k is selected. from this example calculation, for v out = 1.8v, use r9 = 120k and r8 = 60.4k. a table of example output voltages and corresponding resistor values is provided below. table 2: example output voltages and corresponding resistor values power efficiency and device evaluation the charge pump efficiency discussion in the fol- lowing sections accounts only for efficiency of the charge pump section itself. due to the unique circuit architecture and design of the aat2845a, it is very difficult to measure efficiency in terms of a percent value comparing input power over output power. since the aat2845a outputs are pure constant cur- rent sinks and typically drive individual loads, it is difficult to measure the output voltage for a given output (d1 to d4) to derive an overall output power measurement. for any given application, white led forward voltage levels can differ, yet the out- put drive current will be maintained as a constant. this makes quantifying output power a difficult task when taken in the context of comparing to other white led driver circuit topologies. a better way to quantify total device efficiency is to observe the total input power to the device for a given led current drive level. the best white led driver for a given application should be based on trade-offs of size, external component count, reliability, operating range, and total energy usage... not just % efficiency . the aat2845a efficiency may be quantified under very specific conditions and is dependent upon the input voltage versus the output voltage seen across the loads applied to outputs d1 through d4 for a given constant current setting. depending on the combination of v in and voltages sensed at the current sinks, the device will operate in load switch mode. when any one of the voltages sensed at the current sinks nears dropout, the device will operate in 1.5x or 2x charge pump mode. each of these modes will yield different efficiency values. refer to the following two sections for explanations for each operational mode. 1x mode efficiency the aat2845a 1x mode is operational at all times and functions alone to enhance device power con- version efficiency when v in is higher than the volt- age across the load. when in 1x mode, voltage conversion efficiency is defined as output power divided by input power: the expression to define the ideal efficiency ( ) can be rewritten as: -or- standard 1% values (r9, r11 = 120k) v out (v) r8, r10 ( ) 2.8 160k 2.5 130k 2.0 79.6k 1.8 60.4k 1.5 30.1k (%) = 100 v out v in ?? ?? = p out = v out i out = v out p in v in i out v in = p ou t p in r8 = r9(v out - 1.2v) 1.2v
aat2845a four-channel backlight driver with dual ldos 14 2845a.2007.05.1.0 1.5x and 2x charge pump mode efficiency the aat2845a contains a fractional charge pump which will boost the input supply voltage in the event where v in is less than the voltage required to supply the output. the efficiency ( ) can be simply defined as a linear voltage regulator with an effec- tive output voltage that is equal to one and one half or two times the input voltage. efficiency ( ) for an ideal 1.5x charge pump can typically be expressed as the output power divided by the input power. in addition, with an ideal 1.5x charge pump, the output current may be expressed as 2/3 of the input current. the expression to define the ideal efficiency ( ) can be rewritten as: -or- for a charge pump with an output of 5v and a nom- inal input of 3.5v, the theoretical efficiency is 95%. due to internal switching losses and ic quiescent current consumption, the actual efficiency can be measured at 93%. these figures are in close agreement for output load conditions from 1ma to 100ma. efficiency will decrease substantially as load current drops below 1ma or when the level of v in approaches v out . the same calculations apply for 2x mode, where the output current then becomes 1/2 of the input current. capacitor selection careful selection of the four external capacitors c in , c 1 , c 2 , and c out is important because they will affect turn-on time, output ripple, and transient per- formance. optimum performance will be obtained when low equivalent series resistance (esr) ceramic capacitors are used; in general, low esr may be defined as less than 100m . a value of 1f for all four capacitors is a good starting point when choosing capacitors. if the constant current sinks are only programmed for light current levels, then the capacitor size may be decreased. capacitor characteristics ceramic composition capacitors are highly recom- mended over all other types of capacitors for use with the aat2845a. ceramic capacitors offer many advantages over their tantalum and aluminum elec- trolytic counterparts. a ceramic capacitor typically has very low esr, is lowest cost, has a smaller pcb footprint, and is non-polarized. low esr ceramic capacitors help maximize charge pump transient response. since ceramic capacitors are non-polar- ized, they are not prone to incorrect connection dam- age. equivalent series resistance esr is an important characteristic to consider when selecting a capacitor. esr is a resistance internal to a capacitor that is caused by the leads, internal connections, size or area, material composition, and ambient temperature. capacitor esr is typi- cally measured in milliohms for ceramic capacitors and can range to more than several ohms for tanta- lum or aluminum electrolytic capacitors. ceramic capacitor materials ceramic capacitors less than 0.1f are typically made from npo or c0g materials. npo and c0g materials generally have tight tolerance and are very stable over temperature. larger capacitor values are usually composed of x7r, x5r, z5u, or y5v dielec- tric materials. large ceramic capacitors (i.e., larger than 2.2f) are often available in low-cost y5v and z5u dielectrics, but capacitors larger than 1f are not typically required for aat2845a applications. capacitor area is another contributor to esr. capacitors that are physically large will have a lower esr when compared to an equivalent material smaller capacitor. these larger devices can improve circuit transient response when compared to an equal value capacitor in a smaller package size. (%) = 100 v out 1.5v in ?? ?? = p out = v out i out = v out p in v in 1.5i out 1.5v in = p out p in
aat2845a four-channel backlight driver with dual ldos 2845a.2007.05.1.0 15 evaluation board layout figure 3: aat2845a evaluation board figure 4: aat2845a evaluation board top layer. bottom layer. 1. the "+" indicates that these buttons are pressed and released together. evaluation board user interface the user interface for the aat2845a evaluation board is provided by three buttons and two connec- tion terminals. the board is operated by supplying external power and pressing individual buttons or button combinations. the table below indicates the function of each button or button combination. to power-on the evaluation board, connect a power supply or battery to the dc- and dc+ termi- nals. close the board's supply connection by posi- tioning the j1 jumper to the on position. a red led indicates that power is applied. the evaluation board is made flexible so that the user can disconnect the enable lines from the microcontroller and apply external enable signals. by removing the jumpers from j2, and/or j3, exter- nal enable signals can be applied to the board. external enable signals must be applied to the on pin of each j2, or j3 terminal. when applying external enable signals, considera- tion must be given to the voltage levels. the exter- nally applied voltages should not exceed the sup- ply voltage that is applied to the in pins of the device (dc+). the ldo loads can be connected directly to the evaluation board. for adequate performance, be sure to connect the load between outa/outb and dc- as opposed to some other gnd in the system. table 3: evaluation board user interface. button(s) pushed 1 description data increment the backlight data setting. hold down the button to auto-cycle through the brightness levels. light toggle on/off the backlighting section. set the brightness level using the data button. light+data decrement the backlight data setting. hold down to auto-cycle. enldo toggle on/off the ldos. data+light+enldo reset. clear data and bring all enable lines low.
aat2845a four-channel backlight driver with dual ldos 16 2845a.2007.05.1.0 figure 5: aat2845a section schematic. d1 d2 d3 d4 vout outb out a dc+ 1 2 3 j1 en/set enl c9 100f c6 2.2f c4 2.2f c5 2.2f r8 60.4k r9 120k c3 1.0f c1 1.0f c7 0.1f c2 1.0f r10 160k r11 120k d2 1 fbb 20 d1 2 ldob 3 in 4 pgnd 5 in 6 fba 7 ldoa 8 c2- 9 c2+ 10 outcp 11 c1- 12 c1+ 13 en/set 14 enldo 15 d4 16 d3 17 gnd 18 cbyp 19 u1 aat2845a programmed for 2.8v output programmed for 1.8v output optional 100f capacitor to bypass lab supply
aat2845a four-channel backlight driver with dual ldos 2845a.2007.05.1.0 17 figure 6: mcu section schematic. evaluation board component listing component part# description manufacturer u1 AAT2845AIML-EE-T1 four-channel backlight driver with dual ldos analogictech u2 pic12f675 8-bit cmos, flash mcu; 8-pin pdip microchip d1 - d4 lw m673 mini topled white led; smt osram c1 - c3 grm18x 1.0f, 10v, x5r, 0603, ceramic murata c4 - c6 grm18x 2.2f, 10v, x5r, 0603, ceramic murata c7 grm18x 0.1f, 16v, x7r, 0603, ceramic murata c8 grm31x 1f, 10v, x5r, 1206, ceramic murata c9 tajbx 100f, 10v, 10a, tantalum avx r1 - r3 chip resistor 1k, 5%, 1/4w; 1206 vishay r4, r7 chip resistor 100k, 5%, 1/4w; 1206 vishay r5 chip resistor 330, 5%, 1/4w; 1206 vishay r6 chip resistor 220, 5%, 1/4w; 1206 vishay r8 chip resistor 60.4k, 1%, 1/10w; 0603 vishay r9, r11 chip resistor 120k, 1%, 1/10w; 0603 vishay r10 chip resistor 160k, 1%, 1/10w; 0603 vishay j1 - j3 prpn401paen conn. header, 2mm zip sullins electronics led7 cmd15-21src/tr8 red led; 1206 chicago miniature lamp sw1 - sw3 pts645tl50 switch tact, spst, 5mm itt industries vdd 1 gp5 2 gp4 3 gp3 4 gp2 5 gp1 6 gp0 7 vss 8 pic12f675 u2 c8 1f r5 330 r4 100k r7 100k led7 red 1 2 3 1 2 3 j2 220 r6 data sw1 light sw2 enldo sw3 vin en/set vin 1k r1 1k r2 1k r3 dc- j3 enl
aat2845a four-channel backlight driver with dual ldos 18 2845a.2007.05.1.0 ordering information package information 3 tqfn34-20 all dimensions in millimeters. package marking 1 part number (tape and reel) 2 tqfn34-20 yexyy AAT2845AIML-EE-T1 1. xyy = assembly and date code. 2. sample stock is generally held on part numbers listed in bold . 3. 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 re quired to ensure a proper bottom solder connection. all analogictech products are offered in pb-free packaging. the term pb-free means semiconductor products that are in compliance with current rohs standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. for more information, please visit our website at http://www.analogictech.com/pbfree. top view side view detail "a" bottom view 3.00
aat2845a four-channel backlight driver with dual ldos 2845a.2007.05.1.0 19 advanced analogic technologies, inc. 830 e. arques avenue, sunnyvale, ca 94085 phone (408) 737- 4600 fax (408) 737- 4611 ? advanced analogic technologies, inc. analogictech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an analogictech pr oduct. no circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. analogictech reserves the right to make changes to their products or specifications or to discontinue any product or service with- out notice. except as provided in analogictechs terms and conditions of sale, analogictech assumes no liability whatsoever, an d analogictech disclaims any express or implied war- ranty relating to the sale and/or use of analogictech products including liability or warranties relating to fitness for a part icular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. in order to minimize risks associated with the customers applications, adequa te design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. testing and other quality control techniques are utilized to the extent an alogictech deems necessary to support this warranty. specific testing of all parameters of each device is not necessarily performed. analogictech and the analogictech logo are trad emarks of advanced analogic technologies incorporated. all other brand and product names appearing in this document are registered trademarks or trademarks of their respective holder s.

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