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AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 1409.2010.05.1.1 1 www.analogictech.com 1. the maximum number of leds in each string is dependent upon the maximum v f of the diodes in that string. under no event should the voltage at lx be exceeded. general description the AAT1409 is a highly integrated, high efficiency led backlight solution for notebook computers, monitors and portable tvs. the device operates from dc inputs, ciga- rette lighter adapters, or multi-cell li-ion batteries over the 4.5v to 26v voltage range. an integrated boost (step-up) converter provides up to 45v output for driving series leds. eight precision cur- rent sinks are programmed up to 45ma per string through one external r set resistor, supporting up to 88 1 white leds at 360ma total output current. led strings may be disabled or operated in parallel for increased drive capability. the boost output voltage is set by the led string with the highest voltage require- ment, allowing a wide range of led characteristics. the pwm dimming range at 100hz is up to 1,000:1. the boost switching frequency is selectable (up to 1.3mhz) to allow optimum efficiency and the smallest external l/c filtering components. alternatively, the device may be synchronized to an external clock. boost current mode control provides fast response to line and load transients. integrated light-load mode ensures highest efficiency across the entire load range. fault tolerant circuitry extends system life by disabling open led strings. the unique high voltage current sinks prevent damage resulting from shorted leds. the AAT1409 is available in the pb-free, thermally enhanced 24-pin 3x4 tqfn package. features ? v in range: 4.5v to 5.5v / 5.0v to 26.0v ? lx rated to 50v ? maximum i out : 360ma ? up to 92% efficiency ? high efficiency light-load mode ? 8 led current sinks up to 45ma/each ? 2% accuracy (21ma) ? 2% matching (21ma) ? flexible configurations ? disable or parallel ? switching frequency options ? 675khz or 1.3mhz ? synchronize to system clock ? pwm direct dimming input ? up to 100khz prevents audio interference ? fast turn-on/off ? wide 1,000:1 dimming range (100hz) ? fault tolerant: open/short led(s) ? current limit protection ? over-voltage protection ? over-temperature protection ? soft-start minimizes inrush current ? tqfn34-24 low profile package ? -40c to +85c temperature range applications ? monitors ? notebook computers ? portable tv ? portable dvd players ? white led backlight datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 2 1409.2010.05.1.1 www.analogictech.com typical application lx r4 ovp d 1 up to 88 wled backlight AAT1409 tqfn34-24 r1 c3 r3 cs1 cs2 cs3 cs4 cs5 cs6 cs7 cs8 comp sync c4 2.2f 50v 0805 pgnd sgnd rset vin vcc gnd fset c1 2.2f 50v 0805 c2 2.2f 6.3v 0603 en pwm v out : 45v at 240ma r2 v in : 4.5vC26v l1 4.7h datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 1409.2010.05.1.1 3 www.analogictech.com pin descriptions pin # symbol function description 1 sync i synchronizes switching frequency to external system clock. tie to gnd to disable this feature. 2 fset i connect logic high to set internal oscillator to 1300khz. connect logic low to set internal oscil- lator to 675khz. 3, 4, 18, 21 gnd gnd connect to gnd 5 pwm i direct pwm input pin. connect logic level pwm input signal in the frequency range 100hz- 100khz to this pin to enable pwm dimming. 6 cs1 o output current sink 1. connect to sgnd to disable channel 1. 7 cs2 o output current sink 2. connect to sgnd to disable channel 2. 8 cs3 o output current sink 3. connect to sgnd to disable channel 3. 9 cs4 o output current sink 4. connect to sgnd to disable channel 4. 10 sgnd gnd current sink ground tied to return of internal current sinks cs1-cs8. 11 cs5 o output current sink 5. connect to sgnd to disable channel 5. 12 cs6 o output current sink 6. connect to sgnd to disable channel 6. 13 cs7 o output current sink 7. connect to sgnd to disable channel 7. 14 cs8 o output current sink 8. connect to sgnd to disable channel 8. 15 rset i connect resistor to ground to set maximum current through the led strings. 16 comp i connect an external resistor and capacitor to ground to compensate the boost converter. 17 ovp i over-voltage protection pin. connect resistive divider between vout and gnd. care should be taken to ensure that the voltage at lx does not exceed its maximum rating under extreme operating conditions. 19 lx o switching node of boost converter. connect an inductor between this pin and input voltage source. connect the anode of schottky diode between this pin and the boost output capacitor. 20 pgnd gnd power ground; tied to source of integrated nmos switching device. 22 vcc i/o internal regulated voltage when operating from input voltage range 5.0v to 26.0v. de-couple with a 2.2 f capacitor to ground. do not source current from this node. input voltage pin when operating from input voltage range 4.5v to 5.5v. 23 en i logic high enable pin. pull logic high or tie to in to enable the device. pull low to disable the device and minimize quiescent current; pulling low also disables the internal linear regulator. 24 in i input voltage to ic. tied to input voltage source and input boost inductor. ep gnd exposed paddle. connect to pcb gnd plane. pcb paddle should maintain acceptable junction temperature. pin configuration tqfn34-24 (top view) 1 2 3 4 5 6 7 8 9 24 23 22 21 20 10 11 12 19 18 17 16 15 14 13 sync fset gnd gnd pwm cs1 cs2 cs3 cs4 sgnd cs5 cs6 comp ovp rset cs8 cs7 gnd lx ep pgnd gnd vcc en in datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 4 1409.2010.05.1.1 www.analogictech.com 1. stresses above those listed in absolute maximum ratings may cause permanent damage to the device. functional operation at co nditions 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. mounted on an fr4 board. 4. derate 20mw/c above 25c. absolute maximum ratings 1 symbol description value units v lx lx voltage to gnd 50 v v in,en input voltage, en to gnd -0.3 to 30 v csx output current sinks cs1 ? cs8 to gnd -0.3 to 32 v cc vcc voltage to gnd -0.3 to 7.0 ovp, comp, pwm, sync, rset, ovp, comp, pwm, sync, clk voltage to gnd -0.3 to v cc + 0.3 i out maximum dc output current 2 375 ma t j maximum junction operating temperature -40 to +150 c t lead maximum soldering temperature (at leads, 10 sec) 300 p d maximum power dissipation 3 2w ja thermal resistance 3,4 50 c/w recommended operating conditions symbol description value units v in input voltage range 5 to 26 v v out output voltage range v in + 3 to 45 f pwm pwm dimming frequency range 0.1 to 100 khz i out dc output current 160 to 240 ma t a operating ambient temperature -40 to 85 c t j operating junction temperature -40 to 125 c datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 1409.2010.05.1.1 5 www.analogictech.com 1. the AAT1409 is guaranteed to meet performance specifications over the -40c to +85c operating temperature range and is assu red by design, characterization, and correla- tion with statistical process controls. 2. output voltage must result in a voltage lower than the lx maximum rating under all operating conditions. electrical characteristics 1 v in = 12v; c in = 4.7 f, c out = 2.2 f; c vcc = 2.2 f; l 1 = 10 h; r set =7.5k (i csx = 21ma); t a = -40 o c to 85 o c unless otherwise noted. typical values are at t a = 25 o c. symbol description conditions min typ max units power supply, current sinks v in input voltage range v in = v cc 4.5 5.5 v v cc = open 5.0 26.0 v uvlo under voltage threshold v in rising 4.3 v hysteresis 500 mv v in falling 3.2 v v cc v cc output voltage en = logic high, i cc(out) = 0ma 4.0 4.5 6 v v cx current sink voltage en = logic high, i csx = 21ma (r set = 7.5k ) 0.5 v i q in quiescent current (no switching) i csx = 0% , v csx = 0.5v, en = logic high 1.5 ma i sd in pin shutdown current cs1-cs8 = open, en = logic low, does not include lx leakage current 40.0 a i csx current sink accuracy i csx = 21ma -5 2 +5 % i csx-matching current matching between any sink channel i csx = 21ma -3 2 +3 % v ovp over-voltage threshold v out rising 1.1 1.2 1.3 v over-voltage hysteresis v out falling 100 mv r ds(on)lo low side switch on resistance v cc = 4.5v 200 m d max maximum duty cycle 90 % t min minimum on-time 100 ns i csx / i rset current set ratio i csx /i rset , v rset = 0.6v 262 a/a i limit low side switch current limit 3.0 6.5 a i leak lx pin leakage en = logic low; v lx = 40v 1 a csx pin leakage en = logic low, csx = 30v 10 a f osc oscillator frequency fset = logic low; v in = 5.0 to 26.0v; v in = v cc = 4.5 to 5.5v 550 675 800 khz fset = logic high; v in = 5.0 to 26.0v; v in = v cc = 4.5 to 5.5v 1100 1300 1500 khz f sync sync frequency f osc 20% khz f sync sync duty cycle range f osc 20% 10 90 % f pwm(max) maximum direct pwm frequency 50 100 khz t ss soft-start time v out = 35v, c comp = 18nf, r comp = 10k 1ms logic level inputs: en pin v en(l) threshold low 0.4 v v en(h) threshold high 2.5 v i len input leakage enable pin v en = 5v, v in = 5v 3 a logic level inputs: sync, pwm, fset pins v (h) threshold low 0.4 v v (h) threshold high 1.4 v i lk input leakage v sync = v pwm = v fset = 5v -1 1 a t pwm(on/off) pwm turn on/off delay pwm transition to 95%/5% i rset 1 s thermal protection t j(sd) t j thermal shutdown threshold 140 c t j(hys) t j thermal shutdown hysteresis 15 c datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 6 1409.2010.05.1.1 www.analogictech.com typical characteristics boost efficiency vs. input voltage (l = 10h; v cc = 4.7v; pwm = v cc ; f set = gnd; i out = 360ma) input voltage (v) efficiency (%) 61014182226 812162024 20 30 40 50 60 70 80 90 100 v out = 29v v out = 36v boost efficiency vs. load current (l = 10h; v cc = 4.7v; pwm = v cc ; f set = gnd) output current (ma) efficiency (%) 10 80 150 220 290 45 115 185 255 360 325 20 30 40 50 60 70 80 90 100 v in = 9v, v out = 28v v in = 12v, v out = 36v v in = 24v, v out = 46v boost efficiency vs. pwm duty cycle (l = 10h; v cc = 4.7v; f set = gnd) pwm duty cycle (%) efficiency (%) 0 20 40 60 80 100 10 30 50 70 90 20 30 40 50 60 70 80 90 100 v in = 9v, v out = 29v v in = 12v, v out = 36v v in = 24v, v out = 45v output current vs. pwm duty cycle (v in = 12v; i csx = 20ma/ch) pwm duty cycle (%) total output current (ma) 0 20 40 60 80 100 10 30 50 70 90 0 20 40 60 80 100 120 140 160 low side switch current limit vs. temperature (v in = 5v to 26v) temperature (c) current limit (a) -40 -15 10 35 60 85 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 v cc line regulation vs. input voltage input voltage (v) v cc (v) 61014182226 812162024 4.3 4.35 4.4 4.45 4.5 4.55 4.6 4.65 4.7 85c 25c -40c datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 1409.2010.05.1.1 7 www.analogictech.com typical characteristics quiescent current vs. input voltage (non-switching; v csx = 0.5v; i csx =0ma) input voltage (v) quiescent current (ma) 61014182226 812162024 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 85c 25c -40c shutdown current vs. input voltage (v lx = v csx = open) input voltage (v) shutdown current (a) 61014182226 812162024 0 2 4 6 8 10 12 14 16 18 20 85c 25c -40c switching frequency vs. temperature (v in = 12v) temperature (c) switching frequency error (%) -40 -15 10 35 60 85 -4 -3 -2 -1 0 1 2 3 4 fset = gnd fset = v cc over-voltage threshold vs temperature (v in = 12v) temperature (c) ovp voltage (v) -40 -15 10 35 60 85 1.1 1.12 1.14 1.16 1.18 1.2 1.22 1.24 1.26 1.28 1.3 current sink accuracy vs. temperature (v in = 12v; v csx = 0.8v; i csx = 21ma/channel) temperature (c) current sink accuracy (%) -40 -15 10 35 60 85 -4 -3 -2 -1 0 1 2 3 4 current sink matching vs. temperature (v in = 12v; v csx = 0.8v; i csx = 21ma/channel) temperature (c) current sink matching (%) -40 -15 10 35 60 85 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 8 1409.2010.05.1.1 www.analogictech.com typical characteristics startup (v in = 12v; v out = 37v; c out = 2.2f; l = 4.7h; i out = 160ma) time (100s/div) en (10v/div) v out (20v/div) i out (100ma/div) i lx (2a/div) 12v switching waveforms (v in = 12v; v out = 37v; c out = 2.2f; l = 4.7h; i out = 160ma) time (500ns/div) v out (ac coupled) (200mv/div) v in (ac coupled) (50mv/div) i lx (1a/div) pwm switching waveforms (v in = 12v; v out = 37v; c out = 2.2f; l = 4.7h; i out = 160ma) time (100s/div) i out (100ma/div) v out (1v/div) pwm (5v/div) i lx (1a/div) 37v datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 1409.2010.05.1.1 9 www.analogictech.com functional description the AAT1409 is a highly integrated, high efficiency white led backlight solution for notebook computers, monitors and portable tvs. the device operates from regulated dc inputs, cigarette lighter adapters, and multi-cell li-ion batteries over a voltage range from 4.5v to 26v. the integrated boost (step-up) converter provides up to 45v output to drive multiple strings of series leds. the maximum number of leds is dependent upon the for- ward voltage of each led. eight precision current sinks can provide constant current drive for up to 88 white leds depending upon led v f . the led current is set by a single external resistor up to 45ma per string for a total output current capability of 360ma. the controller derives output feedback from the channel with the lowest current sink voltage while maintaining the programmed current in each led string. this ensures the lowest pos- sible output voltage, highest efficiency and continuous operation with mismatched led strings. the AAT1409 is designed for maximum flexibility. the led strings may be disabled or used in parallel for increased current capability. thus, the AAT1409 allows operation with fewer than 8 led strings with the maximum number of leds per channel set by the led v f and the output volt- age of the boost converter. a lower number of leds can also be used. unused current sinks are disabled by tying them to ground. the unique high voltage current sinks support non-matching led strings (led quantity, type, etc.). for high current applications, such as high- bright- ness leds, multiple current sinks may be connected in parallel providing up to 360ma per led string. the AAT1409 supports a high input pwm frequency to help eliminate potential audio emissions caused by har- monic/sub-harmonic resonance of the power stage. the pwm dimming range is up to 1,000:1 (see figure 1). the output voltage is regulated by the string with the highest voltage requirement, allowing a wide range of led characteristics. the boost switching frequency is functional block diagram logic lx cs1 in vcc linear reg en sync cs2 cs3 cs4 rset gnd pgnd cs5 cs6 cs7 cs8 ovp v ref comp pwm sgnd p p s s osc fset datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 10 1409.2010.05.1.1 www.analogictech.com adjustable up to 1300khz for optimum efficiency and the smallest external filtering components. alternatively, the device may be synchronized to an external clock. current mode control provides fast response to line and load transients. integrated light load mode ensures highest efficiency across the entire input voltage and load range. fault tolerant circuitry extends system life by disabling open led strings. the high voltage current sinks main- tain normal operation with non-matched strings while also preventing damage due to shorted leds. the AAT1409 is available in a pb-free, thermally enhanced 24-pin 3x4mm tqfn package. pwm dimming the AAT1409 provides direct pwm dimming. after initial power-up or when en is cycled, the device is enabled with brightness (default) controlled by the pwm duty cycle and the r set resistor value. the ultra-fast 1 s turn-on and turn-off time of the boost regulator and current sinks ensures high performance and excellent dimming range in applications requiring high frequency pwm dimming. the high pwm dimming frequency eliminates audio interference. the integrated current sinks ensure good timing between strings (pwm matching) while the fast response yields a linear pwm duty-cycle versus led current characteristic. pwm inputs from 100hz to 100khz are recommended. AAT1409 dimming range vs. pwm pin frequency pwm frequency (hz) dimming range 1 10 100 1000 10000 100000 1 10 100 1000 10000 100000 figure 1: pwm input frequency vs. dimming range. fault tolerant operation the AAT1409 device is protected from faults arising from led opens and/or shorts. an led open condition will be detected by the controller at startup and during normal operation. the low voltage on the current sink is detected by the controller, which disables the feedback to the boost converter from that current sink. the remaining led strings continue to operate normally. the controller re-enables the current sink feedback if the led open condition is removed dur- ing a power or en cycle. this feature extends backlight life and reliability, which is otherwise limited by intermit- tent conditions in the led string(s) and/or circuit board interconnections. under all conditions, the over-voltage protection circuitry prevents the switching node (lx) from exceeding the maximum operating voltage prior to disabling the current sink. over-voltage protection (ovp) disables boost switch- ing while maintaining the programmed led current. boost switching is re-enabled when ovp hysteresis is satisfied. a led short condition results in a higher voltage appear- ing on the affected channels' current-sink pin. the affected current sink automatically compensates for the additional voltage. the current sink can withstand a high voltage indefinitely. however, the increased voltage across the current sink causes an increase in power dissipation. the channel will continue to operate until the over-tem- perature protection activates. integrated over-current protection is provided. over- current protection prevents inductor saturation and any resulting damage to the switching device occurring dur- ing an overload fault condition. datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 1409.2010.05.1.1 11 www.analogictech.com lx ovp r2 c1 c4 d1 l1 r3 r4 1.2v vin v out v cc i r2 262 .i r2 v rset = 0.6v figure 2: over-voltage protection and current sink setting circuit. application information ovp protection with open led failure the ovp protection consists of a resistive divider net- work (r3 and r4) as shown in figure 2. the resistor divider must be selected so that the voltage at the ovp pin exceeds the ovp rising threshold when the output is at v out(max) . r3 = r4 - 1 v out(max) v ovp(max) when the ovp rising threshold is exceeded, the con- verter stops switching. the open led channel is removed from the boost converter feedback loop. when the volt- age at the ovp pin falls below the ovp hysteresis volt- age, the boost converter can resume switching. it is important that during normal operation the current sinks are given enough headroom so that the ovp threshold is not tripped. the output voltage at the minimum ovp threshold is v out(min) = v ovp(min) + 1 r 3 r 4 the maximum voltage of each led string including the current sink headroom should not exceed v out(min) . v out(min) > v csx + n v fled(max) v ovp(min) + 1 > v csx + n v fled(max) r 3 r 4 r3 > r4 v csx + n v fled(max) - v ovp(min) v ovp(min) where: n is the number of leds in each string. v ovp(min) = 1.1v is minimum over voltage threshold. v csx = 0.5v is the current sink voltage. v fled(max) is the maximum led forward voltage at 20ma. datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 12 1409.2010.05.1.1 www.analogictech.com another factor in setting the ovp voltage using the resis- tive divider is that the maximum voltage at the lx pin does not exceed v lx(max) = 50v. v lx(max) = v out(max) + v d1 + v ring v d1 is the forward voltage of the schottky diode d1 v ring is the voltage spike at the lx node caused by the delay of d1 at turn on. measurements should confirm that the maximum switch- ing node voltage v lx(max) is less than 50.0v under worst case conditions. for example, if the number of white leds in each string is n =11, the resistor divider r3 can be calculated by selecting r4 = 12.1k : r3 > 12.1k = 441.1k 0.5v + 11 3.7v - 1.1 1.1 choose r3 = 442k . the maximum output voltage with the selected values of r4, r3 is v out(max) = v ovp(max) + 1 = 48.8v r 3 r 4 led current sink setting the current sink is controlled by the r set voltage (0.6v) and the r set resistor (r2). for maximum accuracy, a 1% tolerance resistor is recommended. the r set resistor (r2) value can be calculated as follows: r 2 = 262 0.6v i csx(max) where v rset = 0.6v. for example, if the maximum current for each string of leds is 30ma, this corresponds to a minimum resistor value of 5.23k . r 2 = = 5.23k 262 0.6v 30ma maximum i led current (ma) r2 (k ) 45 3.48 30 5.23 25 6.19 20 7.87 15 10.5 10 15.8 5 31.6 table 2: maximum led current sink vs. r set resistor (r2) values. schottky diode selection to ensure minimum forward voltage drop, high voltage schottky diodes are considered the best choice for the white led boost converter. the output diode is sized to maintain acceptable efficiency and reasonable operating junction temperature under full load operating condi- tions. forward voltage (v f ) and package thermal resis- tance ( ja ) are the dominant factors to consider in selecting a diode. the diode non-repetitive peak forward surge current rating (i fsm ) should be considered for high pulsed load applications. i fsm rating drops with increasing conduction period. manufacturers? datasheets should be consulted to verify reliability under peak loading condi- tions. the diode?s published current rating may not reflect actual operating conditions and should be used only as a comparative measure between similarly rated devices. during the on-time, the output voltage on the output cap is applied to the cathode of the external schottky diode. the rectifier's reverse breakdown voltage rating should be greater than the maximum output voltage rating of the boost. 40v rated schottky diodes are recommended for outputs less than 30v, while 60v rated schottky diodes are recommended for outputs greater than 35v. the average diode current is equal to the output cur- rent. i avg = i out datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 1409.2010.05.1.1 13 www.analogictech.com the approximate power loss on the schottky diode can be determined: p loss-diode = i avg v f = i out v f diode junction temperature can be estimated. t j = t amb + ja p loss-diode output diode junction temperature should be maintained below 110c, but may vary depending on application and/or system guidelines. the diode ja can be minimized with additional pcb area on the cathode. pcb heat-sink- ing the anode may degrade emi performance. the reverse leakage current of the rectifier must be consid- ered to maintain low quiescent (input) current and high efficiency under light load. the rectifier reverse current increases dramatically at elevated temperatures. inductor selection the white led boost (step-up) converter is designed to operate with a minimum inductor value of 4.7 h for all input and output voltage combinations. the inductor saturation current rating should be greater than the nmos current at maximum duty cycle. d max = (v out + v f - v in(min) ) v out + v f the inductor (l) is selected to avoid saturation at mini- mum input voltage, maximum output load conditions. peak current may be calculated from the following equa- tion, again assuming continuous conduction mode. worst-case peak current occurs at minimum input volt- age (maximum duty cycle) and maximum load. i peak = + i out 1 - d max d max v in(min) 2 f s l output capacitor the high output ripple inherent in the boost converter necessitates low impedance output filtering. multi-layer ceramic (mlc) capacitors provide small size and adequate capacitance, low parasitic equivalent series resistance (esr) and equivalent series inductance (esl), and are well suited for use with the white led boost regulator. mlc capacitors of type x7r or x5r are recommended to ensure good capacitance stability over the full operating temperature range. the output capacitor is sized to maintain the output load without significant voltage droop ( v out ) during the power switch on interval, when the output diode is not conducting. a ceramic output capacitor from 2.2 f to 4.7 f is recommended. typically, 50v rated capacitors are required for the 42v maximum boost output. ceramic capacitors sized as small as 0805 or 1206 are available which meet these requirements. mlc capacitors exhibit significant capacitance reduction with applied voltage. output ripple measurements should confirm that output voltage droop and operating stability are acceptable. voltage derating can minimize this fac- tor, but results may vary with package size and among specific manufacturers. the output capacitor size can be estimated using the equation: c out = i out d max f s ?v out to maintain stable operation at full load, the output capacitor should be sized to maintain v out between 100mv and 200mv. the wled boost converter input current flows during both on and off switching intervals. the input ripple current is less than the output ripple and, as a result, less input capacitance is required. compensation component selection the AAT1409 boost architecture uses peak current mode control to eliminate the double pole effect of the output l&c filter and simplifies the compensation loop design. the current mode control architecture simplifies the transfer function of the control loop to be a one-pole, one left plane zero and one right half plane (rhp) system in the frequency domain. the dominant pole can be cal- culated by: f p = 1 2 r 0 c 4 datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 14 1409.2010.05.1.1 www.analogictech.com c4 d1 l1 r o esr vin vout i out figure 3: AAT1409 equivalent output stage. the esr zero of the output capacitor (see figure 3) can be calculated by: f z_esr = 1 2 r esr c 4 where: c 4 is the output filter capacitor r o is the equivalent load resistor value r esr is the equivalent series resistance of the output capacitor. the right half plane (rhp) zero can be calculated by: f z_esr = v in 2 2 l 1 i out v out it is recommended to design the bandwidth to one decade lower than the frequency of rhp zero to guaran- tee the loop stability. a series capacitor and resistor network (r1 and c3) connected to the comp pin sets the pole and zero which are given by: f p_com = 1 2 r ea c 3 f z_com = 1 2 r 1 c 3 where: c 3 is the compensation capacitor r 1 is the compensation resistor r ea is the output resistance of the error amplifier (2.97m ). a 15nf (c3) capacitor and a 5k (r1) resistor in series are chosen for optimum phase margin and fast transient response. datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 1409.2010.05.1.1 15 www.analogictech.com r3 442k r4 12.1k mss1p6 d1 v in 5v - 26v c4 2.2f 50v 0805 r2 7.5k r1 4.99k c1 10f 35v c2 2.2f 10v c3 15nf jp4 jp2 v out pwm 5 cs2 7 gnd cs1 6 cs3 8 cs4 9 sgnd cs5 11 rset 15 comp 16 ovp 17 gnd gnd fset 2 sync 1 cs6 12 cs7 13 cs8 14 lx 19 pgnd gnd in 24 en 23 vcc 22 AAT1409 u1 tqfn34-24 10 leds in series 4 3 10 18 21 20 ep l1 sumida, cdrh5d28rhpnp-4r7n, 4.7h, 3.7a, dcr = 43.1m d1 vishay, schottky barrier diode, mss1p6, 1a, 60v c1 taiyo yuden, gmk325bj106kn-t, 10f, 35v, x5r,1210; or murata grm32er71h106k, 10f, 50v, x7r, 1210 c2 2.2f, 10v, 0603 c3 cap, 15nf, 10v, 0603 c4 murata, grm31cr71h225ka88l, 2.2f, 50v, x7r, 1206 r1, r2, r3, r4 carbon film resistors, 1%, 0603 l1 4.7h jp1 jp3 figure 4: AAT1409imk evaluation board schematic. figure 5: AAT1409imk evaluation board figure 6: AAT1409imk evaluation board top side layout. bottom side layout. datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 16 1409.2010.05.1.1 www.analogictech.com 60v or higher output voltage applications the maximum voltage of the lx pin cannot exceed 50v that limits the output voltage of AAT1409 to less than 50v. for larger panel driver applications where the num- ber of leds in each string exceeds the maximum leds supported by the AAT1409, a high voltage external n-channel mosfet q1 is stacked to the lx pin to protect the internal low-side switch from the output voltage greater than 50v. as illustrated in figure 7, two AAT1409s are connected in master and slave configuration in order to drive 16 parallel strings with 18 leds in series for each string. the master has a boost configuration with inductor l1, schottky diode d1, and high voltage n-channel mosfet q1, while the slave operates as addi- tional 8-channel current sinks. the lx pins, vout, ovp pins, sync pins, and pwm pins of the master and slave should be connected together for synchronization. the gate of q1 is connected to the input voltage via a resis- tive divider (r9 and r10) to keep its gate to source volt- age within the maximum rating (20v). high voltage mosfet selection during the off-time, the energy stored in the inductor boosts-up the drain terminal of q1 to v out + v d1 . during the on-time, the lx node pulls-down the source terminal of q1 to gnd. therefore, the n-channel mosfet q1 must have a maximum operating v dss exceeding the maximum output voltage (v out(max) = 60v for 18 leds in series). the conduction loss (p loss ) for a given mosfet r ds(on) can be calculated in the following equation: p loss = d r ds(on) i l(avg) 2 + ?i l 2 12 where: d is the duty cycle i l(avg) is average inductor current ? i l is the peak-to-peak inductor current. datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 1409.2010.05.1.1 17 www.analogictech.com r3 732k 12.1k r4 ss38 d1 v in c4 2.2f 100v 1210 15nf c3 4.99k r1 7.5k r2 c1 10f 35v c2 2.2f 10v v out = 60v pwm 5 cs2 7 gnd cs1 6 cs3 8 cs4 9 sgnd cs5 11 rset 15 comp 16 ovp 17 gnd gnd fset 2 sync 1 cs6 12 cs7 13 cs8 14 lx 19 pgnd gnd in 24 en 23 vcc 22 AAT1409 u1 18 leds in series 4.7h 4 3 10 18 21 20 ep l1 12v-26v 732k r7 12.1k r8 c8 2.2f 100v 1210 15nf c7 4.99k r5 7.5k r6 c5 10f 35v c6 2.2f 10v v out = 60v pwm 5 cs2 7 gnd cs1 6 cs3 8 cs4 9 sgnd cs5 11 rset 15 comp 16 ovp 17 gnd gnd fset 2 sync 1 cs6 12 cs7 13 cs8 14 lx 19 pgnd gnd in 24 en 23 vcc 22 AAT1409 u2 18 leds in series 4 3 10 18 21 20 ep si4480dy q1 sync pwm r9 100k r10 200k c9 2.2f 35v q1: fairchild, fdd86102, n-channel, 8a, v ds = 100v, d-pak l1: cooper bussmann, dr1050-4r7-r, 4.7h, 6.7a, dcr = 11.9m d1: fairchild, schottky barrier diode, ss38, 3a, 80v c1, c5: taiyo yuden, gmk325bj106kn-t, 10f, 35v, x5r, 1210; or murata grm32er71h106k, 10f, 50v, x7r, 1210 c2, c6: 2.2f, 10v, 0603 c3, c7: cap, 15nf, 10v, 0603 c4, c8: murata, grm32er72a225ka35l, 2.2f, 100v, x7r, 1210 figure 7: application schematic for 60v/320ma output, 288leds using master and slave configuration. datasheet.in
AAT1409 8 channel led backlight driver with integrated boost and high frequency direct pwm dimming switchreg tm product datasheet 18 1409.2010.05.1.1 www.analogictech.com advanced analogic technologies, inc. 3230 scott boulevard, santa clara, ca 95054 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 speci cations or to discontinue any product or service without notice. except as provided in analogictech?s terms and conditions of sale, analogictech assumes no liability whatsoever, and analogictech disclaims any express or implied warranty re lating to the sale and/or use of analogictech products including liability or warranties relating to tness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right . in order to minimize risks associated with the customer?s applications, adequate 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 analogictech deems necessary to support this warranty. speci c testing of all parameters of each device is not necessarily performed. analogictech and the analogictech logo are trademarks of advanced analogic technologies incorporated. all other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders. 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 required to ensure a proper bottom solder c onnection. ordering information package marking 1 part number (tape and reel) 2 tqfn34-24 d1xyy AAT1409imk-t1 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/aboutus/quality.php. package information tqfn34-24 3 3.000 all dimensions in millimeters. datasheet.in

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