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lt1942 1 1942fb the lt 1942 is a highly integrated quad switching regu- lator designed to provide all necessary power supply functions for tft displays, including the white led backlight driver. the tft supply incorporates two boost and one inverting dc/dc converters. the tft supply output voltages are independently set, unlike charge pump solutions which have many limitations. power sequencing for the tft supply is built into the part and is user programmable. the led driver is a boost dc/dc converter that can be independently controlled. the led driver has built-in dimming control for precise control of led current. an 8:1 dimming range is achieved by adjusting the ctrl4 volt- age. the user can elect to drive a single string or two strings of leds. an led ballast circuit is included to precisely match the led currents if two strings of leds are used. soft-start is built into the led driver as well as the primary tft supply. the lt1942 is available in a low profile (0.75mm) 24-lead qfn (4mm 4mm) package. triple output tft supply with built-in power sequencing integrated white led backlight driver integrated schottky diodes active ballast circuitry ensures precise current matching in white leds low noise 1mhz fixed frequency operation 2.6v to 16v input voltage range soft-start limits inrush current tft supply output voltages independently set (not charge pump derived) power good and output disconnect for tft supply built-in led dimming capability open led protection for led driver 24-lead qfn package (4mm 4mm) quad dc/dc converter for triple output tft supply plus led driver poly-silicon tft displays amorphous silicon tft displays ctrl4 sgnd/ agnd d3 sw3 lt1942 sw1 fb1 pgnd14 pgood sw4 d4 led1 led2 fb4 fb3 pgnd23 v out3 nfb2 d2 sw2 0.1 f 0.22 f 47 h v in 47 h shdn v cc ss1 ss4 ct 22 h 22 h cmdsh-3 si2301bds 33 h 301k 1m 100k v in 4.7pf 0.1 f 0.1 f 0.1 f 1942 ta01 0.22 f 2.2 f shutdown led control av dd 5v 40ma 4.7 f 4.7 f 698k 100k 10k v in 3v to 4.2v v on 10v 2ma v off ?0v 2ma 665k 4.99 ? 20ma 20ma tft bias and white led backlight power supply applicatio s u descriptio u features , lt, ltc and ltm are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. typical applicatio u
lt1942 2 1942fb order options tape and reel: add #tr lead free: add #pbf lead free tape and reel: add #trpbf lead free part marking: http://www.linear.com/leadfree/ v cc voltage............................................................. 16v sw1, sw2, sw3 voltage .......................... 0.4v to 36v sw4 .......................................................... 0.4v to 45v fb1, fb3 voltage ................................................... 2.5v fb4 voltage ....................................................... 400mv nfb2 voltage ................................................... 200mv shdn voltage ......................................................... 10v ctrl4 voltage ........................................................ 16v ss1, ss4 voltage .................................................. 1.5v current into d2 ......................................................... 1a d2 voltage ............................................................ 36v current out of d3 ..................................................... 1a d3 voltage .............................................................. 36v current out of d4 ..................................................... 4a d4 voltage .............................................................. 45v led1, led2 voltage ............................................... 45v current into led1, led2 ..................................... 35ma pgood voltage ...................................................... 16v v out3 voltage ......................................................... 36v ct current ........................................................... 1ma maximum junction temperature ......................... 125 c operating temperature range (note 2) .. 40 c to 85 c storage temperature range ................ 65 c to 125 c order part number (note 1) absolute axi u rati gs w ww u package/order i for atio uu w consult ltc marketing for parts specified with wider operating temperature ranges. lt1942euf t jmax = 125 c, ja = 37 c/w, jc = 4.3 c/w exposed pad (pin 25) is sgnd (must be soldered to pcb) the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v in = 3.3v, v shdn = v in , unless otherwise noted. (note 2) parameter conditions min typ max units quiescent current v shdn = 3.3v, v ctrl4 = 0v, not switching 710 ma v shdn = v ctrl4 = 0v, in shutdown 01 a input voltage range v cc pin 2.6 16 v av dd feedback voltage fb1 pin 1.225 1.25 1.275 v av dd feedback pin bias current (fb1) fb1 pin (note 3) 15 60 na av dd feedback voltage for power good signal fb1 pin voltage as a percent of nominal voltage 95 97 100 % v off feedback voltage nfb2 pin ?60 ?50 ?40 mv v off feedback pin bias current (nfb2) nfb2 pin (note 3) 25 60 na v on feedback voltage fb3 pin 1.225 1.25 1.275 v v on feedback pin bias current (fb3) fb3 pin (note 3) 25 60 na led feedback voltage fb4 pin, v ctrl4 = 3.3v 190 200 210 mv led feedback pin bias current (fb4) fb4 pin (note 3) 20 60 a led feedback voltage with dimming fb4 pin, v ctrl4 = 1v 85 95 105 mv electrical characteristics 24 23 22 21 20 19 7 8 9 top view 25 uf package 24-lead (4mm 4mm) plastic qfn 10 11 12 6 5 4 3 2 1 13 14 15 16 17 18 pgnd23 sw3 d3 v out3 fb3 nfb2 led1 led2 d4 fb4 fb1 pgood sw2 d2 v cc pgnd14 sw1 sw4 shdn ctrl4 ct agnd ss1 ss4 uf part marking 1942
lt1942 3 1942fb led1-led2 current matching current into each pin = 20ma, v led1 = v led2 0 1.5 % current into each pin = 20ma, |v led1 -v led2 | = 1v 1 2.5 % led1 voltage 20ma into pin, v led2 = 2v, fb4 = 0 1 1.2 v led2 voltage 20ma into pin, v led1 = 2v, fb4 = 0 1 1.2 v led1, led2 maximum current into either pin, v ledx < 1.5v, fb4 = 0 35 ma led1, led2 leakage current v shdn = 0v, v ledx = 45v 1 a av dd maximum duty cycle sw1 pin 88 93 % v off maximum duty cycle sw2 pin 75 86 % v on maximum duty cycle sw3 pin 75 86 % led maximum duty cycle sw4 pin 88 93 % av dd switch current limit at minimum dc (sw1) sw1 pin (note 4) 150 200 250 ma av dd switch current limit at maximum dc (sw1) sw1 pin (note 4) 80 140 200 ma v off switch current limit at minimum dc (sw2) sw2 pin (note 4) 50 80 110 ma v off switch current limit at maximum dc (sw2) sw2 pin (note 4) 30 60 90 ma v on switch current limit at minimum dc (sw3) sw3 pin (note 4) 50 80 110 ma v on switch current limit at maximum dc (sw3) sw3 pin (note 4) 30 60 90 ma led switch current limit at minimum dc (sw4) sw4 pin (note 4) 550 750 900 ma led switch current limit at maximum dc (sw4) sw4 pin (note 4) 450 600 850 ma v off schottky diode forward drop d2 pin, i = 60ma 0.65 v v off schottky diode leakage current d2 pin, v d2 = ?6v 1 a v on schottky diode forward drop d3 pin, i = 60ma 0.65 v v on schottky diode leakage current v d3 = 36v, sw3 = 0v, output disconnect pnp off 1 a led schottky diode forward drop i = 250ma 0.75 v led schottky diode leakage current v d4 = 36v, sw4 = 0v 1 a switching frequency 0.8 1 1.2 mhz shdn pin current v shdn = 3v 70 100 a v shdn = 0v 20 30 na ctrl4 pin current v ctrl4 = 3v 30 60 a v ctrl4 = 0v 60 ?50 na sw1-sw4 leakage current v swx = 36v 0.01 1 a sw1 v cesat i sw1 = 100ma (note 5) 200 300 mv sw2 v cesat i sw2 = 40ma (note 5) 150 250 mv sw3 v cesat i sw3 = 40ma (note 5) 150 250 mv sw4 v cesat i sw4 = 400ma (note 5) 280 400 mv ss1 charging current v ss = 0.5v 1 3 5 a ss4 charging current v ss = 0.5v 1 3 5 a shdn input voltage high 1v shdn input voltage low 0.4 v ctrl4 input voltage high 0.25 v ctrl4 input voltage low 0.1 v the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v in = 3.3v, v shdn = v in , unless otherwise noted. (note 2) parameter conditions min typ max units electrical characteristics
lt1942 4 1942fb the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v in = 3.3v, v shdn = v in , unless otherwise noted. (note 2) parameter conditions min typ max units electrical characteristics pgood leakage current pgood npn off, v pgood = 5v 0 0.1 a pgood sink current pgood npn on, v pgood = 1v 0.5 0.7 ma ct charging current 12 a ct reference voltage 0.8 v v out3 leakage current output disconnect pnp off, d3 = 36v, v out = 0v 0 1 a v out3 source current output disconnect pnp on, d3 = 3v, v out = 2.5v 10 15 ma minimum d3/v out3 operating voltage minimum d3 voltage for proper output 3 v disconnect pnp operation d4 led open-circuit voltage 38 42 44 v note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: the lt1942 is guaranteed to meet performance specifications from 0 c to 70 c. specifications over the 40 c to 85 c operating temperature range are assured by design, characterization and correlation with statistical controls. note 3: current flows out of the pin. note 4: current limit guaranteed by design and/or correlation to static test. note 5: v cesat 100% tested at wafer level. typical perfor a ce characteristics uw v fb1 voltage temperature ( c) ?0 voltage (v) 1.26 1.27 1.28 20 60 1942 g01 1.25 1.24 ?0 0 40 80 100 1.23 1.22 temperature ( c) ?0 ?55 voltage (mv) ?54 ?52 ?51 ?50 ?45 ?48 0 40 60 1942 g02 ?53 ?47 ?46 ?49 ?0 20 80 100 temperature ( c) ?0 voltage (v) 1.26 1.27 1.28 20 60 1942 g01 1.25 1.24 ?0 0 40 80 100 1.23 1.22 nfb2 voltage v fb3 voltage
lt1942 5 1942fb typical perfor a ce characteristics uw fb4 voltage v fb4 vs ctrl4 oscillator frequency temperature ( c) ?0 190 v fb4 (mv) 192 196 198 200 210 204 0 40 60 1942 g04 194 206 208 202 ?0 20 80 100 ctrl4 (v) 0 0 v fb4 (mv) 50 100 150 200 300 0.5 1 1.5 2 1942 g05 2.5 3 250 t a = 40 c t a = 85 c t a = 25 c temperature ( c) ?0 oscillator frequency (khz) 1000 1100 1200 20 60 1942 g06 900 800 ?0 0 40 80 100 700 600 quiescent current ct timer delay time sw1 saturation voltage temperature ( c) ?0 5.0 quiescent current (ma) 5.5 6.5 7.0 7.5 10.0 8.5 0 40 60 1942 g07 6.0 9.0 9.5 8.0 ?0 20 80 100 temperature ( c) ?0 0 delay time (ms) 1 3 4 5 10 7 0 40 60 1942 g08 2 8 9 6 ?0 20 80 100 c t = 0.1 f sw1 current (ma) 0 0 sw1 saturation voltage (mv) 100 200 300 400 50 100 200 150 175 1942 g09 500 600 25 75 125 t a = 25 c sw3 saturation voltage sw2 saturation voltage sw4 saturation voltage sw3 current (ma) 0 sw3 saturation voltage (mv) 150 200 250 30 50 1942 g10 100 50 0 10 20 40 300 350 400 60 t a = 25 c sw2 current (ma) 0 sw2 saturation voltage (mv) 150 200 250 30 50 1942 g10 100 50 0 10 20 40 300 350 400 60 t a = 25 c sw4 current (ma) 0 sw4 saturation voltage (mv) 300 400 500 300 700 1942 g12 200 100 0 100 200 500 600 400 600 700 800 800 t a = 25 c
lt1942 6 1942fb typical perfor a ce characteristics uw led1 to led2 current matching v out3 vs i out3 led open-circuit protection voltage d4 forward voltage v off diode forward voltage av dd switcher current limit led switcher current limit v on diode forward voltage led2 current (ma) 2 6 10 14 18 26 30 led1 current matching error (%) 0 1.0 1942 g13 ?.0 2.0 22 34 2.0 0.5 0.5 ?.5 1.5 t a = 85 c t a = 40 c t a = 25 c v led1 = v led2 + 1v i out3 current (ma) 0.01 200 d3-v out3 voltage drop (mv) 250 300 350 400 0.1 1 10 1942 g14 150 100 50 0 450 500 t a = 85 c t a = 40 c t a = 25 c temperature ( c) ?0 42.0 v out4 voltage (v) 42.2 42.6 42.8 43.0 44.0 43.4 0 40 60 1942 g08 42.4 43.6 43.8 43.2 ?0 20 80 100 d4 current (ma) 400 d4 forward voltage (mv) 800 1200 1400 0.1 10 100 1000 1942 g16 0 1 1000 600 200 t a = 25 c v off diode current (ma) 400 v off diode forward voltage (mv) 800 1200 1400 0.1 10 100 1000 1942 g17 0 1 1000 600 200 t a = 25 c duty cycle (%) 20 i lim (ma) 200 250 300 50 70 1942 g18 150 100 30 40 60 80 90 50 0 t a = 25 c v on diode current (ma) 400 v on diode forward voltage (mv) 800 1200 1400 0.1 10 100 1000 1942 g19 0 1 1000 600 200 t a = 25 c duty cycle (%) 20 0 i lim (ma) 100 300 400 500 60 900 1942 g20 200 40 30 70 80 50 90 600 700 800 t a = 25 c
lt1942 7 1942fb uu u pi fu ctio s pgnd23 (pin 1): power ground for v off and v on switcher. tie directly to local ground plane. sw3 (pin 2): switch pin for v on switcher. this is the collector of an internal npn power switch. minimize the metal trace area connected to this pin to minimize emi. d3 (pin 3): output of v on switcher. place output decoup- ling capacitor from this pin to local ground plane. v out3 (pin 4): collector of internal output disconnect pnp transistor for the v on switcher. place a capacitor from this pin to local ground plane of at least 0.1 f. fb3 (pin 5): feedback pin for v on switcher. reference voltage is 1.25v. connect resistive divider tap here. minimize trace area at fb3. set v out3 according to v out3 = 1.25(1 + r5/r6). nfb2 (pin 6): feedback pin for v off switcher. reference voltage is ?50mv. connect resistive divider tap here. minimize trace area at nfb2. set v out2 according to v out2 = ( 0.15)(1 + r3/r4). shdn (pin 7): shutdown. tie to 1v or greater to enable the part. tie to 0.4v or lower to disable. this pin is the global shutdown pin for all four switching regulators. ctrl4 (pin 8): shutdown for the led switcher. tie to 0.25v or greater to enable the led switcher. tie to 0.1v or lower to disable. ctrl4 can also override the default 200mv reference for the led switcher. if ctrl4 is tied to 2.5v or greater, the reference voltage is 200mv. if ctrl4 is less than 2.5v, the led reference voltage is approximately v ctrl4 /10. this allows an 8:1 dimming range for the leds. refer to the applications section for more information. ct (pin 9): programmable delay for the tft supplies. place a capacitor from this pin to local ground plane. after the delay, the output disconnect pnp for the v on supply is turned on. the delay time is initiated when av dd reaches 97% of its final value. agnd (pin 10): analog ground. tie directly to local ground plane. ss1 (pin 11): soft-start pin for av dd switcher. place a soft-start capacitor from this pin to ground. upon start-up, 3 a of current charges the capacitor to 1.25v. use larger capacitor for slower start-up. leave floating if not in use. ss4 (pin 12): soft-start for led switcher. place a soft- start capacitor from this pin to ground. upon start-up, 3 a of current charges the capacitor to 1.25v. use larger capacitor for slower start-up. leave floating if not in use. pgood (pin 13): power good indication for av dd switcher. open-collector npn. stays open until the v fb1 voltage reaches 97% of target value at which point the pin will pull down. fb1 (pin 14): feedback pin for av dd switcher. connect resistive divider tap here. minimize trace area at fb1. set v out1 according to v out1 = 1.25(1 + r1/r2). fb4 (pin 15): feedback pin for led switcher. place a resistor from this node to ground. choose r7 to set led current (i led ) according to the following formula: if v ctrl4 2.5v, r7 = 0.2/i led in this case, i led is the total led current. if two strings of leds are used, i led is the sum of the current in the two strings. if only a single string of leds is used, i led is simply the single string current. for dimming led current, drive v ctrl4 to a lower voltage. see the applications section for more information. d4 (pin 16): output of led switcher. place output de- coupling capacitor from this pin to local ground plane. led2 (pin 17): second input of current mirror for an led string. connect the negative end of second string of leds to this pin. if not in use, leave floating.
lt1942 8 1942fb uu u pi fu ctio s led1 (pin 18): first input of current mirror for an led string. connect the negative end of first string of leds to this pin. if not in use, leave floating. sw4 (pin 19): switch pin for led switcher. this is the collector of an internal npn power switch. minimize the metal trace area connected to this pin to minimize emi. sw1 (pin 20): switch pin for av dd switcher. this is the collector of an internal npn power switch. minimize the metal trace area connected to this pin to minimize emi. pgnd14 (pin 21): power ground for led switcher and av dd switcher. tie directly to local ground plane. v cc (pin 22): input supply. must be locally bypassed. d2 (pin 23): anode connection of internal schottky diode for v off switcher. sw2 (pin 24): switch pin for v off switcher. this is the collector of an internal npn power switch. minimize the metal trace area connected to this pin to minimize emi. sgnd (pin 25): signal ground. this is the exposed pad, which must be soldered directly to a local ground plane to achieve optimum thermal performance.
lt1942 9 1942fb block diagra w 14 + + + + 28mv fb1 pgood enable ss1 r one shot qs s rq 1.250v reference soft-start comparator av dd boost converter driver 11 sw1 q1 q2 q3 q4 20 pgnd14 13 7 shdn 22 v cc 8 ctrl4 10 agnd ramp-pulse generator + 6 + + nfb2 s rq ?50mv reference 1mhz oscillator comparator v off inverting converter driver sw2 24 d2 d2 ramp-pulse generator + 23 5 + + fb3 s rq 1.250v reference comparator v on boost converter driver sw3 2 d3 d3 3 pgnd23 sw4 ramp-pulse generator + 1 + + fb4 90k 10k 200mv s rq comparator 40v led boost converter driver 19 ss4 enable enable enable ramp-pulse generator + 21 v out3 4 ct 9 d4 d4 pgnd14 1942bd pnp drive delay generator soft-start 12 16 q5 fb4 led2 17 q6 led1 18 15 q7
lt1942 10 1942fb operatio u refer to the figure on the first page of this data sheet and the block diagram when following the description of the operation of the lt1942. the lt1942 contains four switch- ing regulators. three switchers are designed to be used as the power supply for driving small to medium sized tft displays. the fourth switcher is designed to power an led backlight. all four switching regulators use a constant frequency, current mode control scheme to provide excel- lent line and load regulation. tft supply the three switching regulators for the tft supply are named av dd , v off and v on . both the av dd and v on switchers are boost type, while the v off is an inverting type. power sequencing circuitry is integrated into the lt1942 to properly power up the tft power supply. when the shdn pin is driven above 1v initially, only the av dd switcher is enabled. after the output of the av dd switcher reaches 97% of its final value, the pgood pin is driven low and both the v off and v on switchers are enabled. this event is latched rejecting any later drops on av dd below 97%. the output-disconnect circuitry (q5 in the block diagram) for the v on switcher is not activated until the programmable delay set by the ct pin has elapsed. once the output-disconnect circuitry is enabled, the v out3 pin is driven to nearly the same voltage as d3. the v out3 pin can only source current and is limited to 15ma nominally. all three switching regulators are internally compensated and operated at a fixed frequency of 1mhz. the av dd switch- ing regulator has integrated soft-start. simply place a capacitor from the ss1 pin to gnd to implement soft-start. led supply the fourth switching regulator in the lt1942 is designed to drive up to 20 leds (2 strings of 10) to power a backlight. the led switcher has an integrated current ballaster (q6 and q7 in the block diagram) which enables two strings of leds to have active current matching. the current into led1 and led2 will always be actively matched, regardless of which led string has the highest voltage drop. the led ballast circuitry can be left unused when driving a single string of leds. simply leave the led1 and led2 inputs floating and return the led string directly to the fb4 pin. the led switcher has an independent control pin which serves two functions: shutdown and reference adjustment. the ctrl4 pin needs to be driven above 0.25v to enable the led switcher. when ctrl4 is between 0.25v and 2.5v, the internal reference for the led switcher is attenuated. if ctrl4 is above 2.5v, the internal refer- ence is limited to 200mv no matter how high ctrl4 is. this feature allows an 8:1 dimming range for the leds. the led switching regulator is internally compensated and operates at a fixed frequency of 1mhz. the led switching regulator has led open-circuit protection. if any led fails open, d4 is not allowed to exceed 42v (typical). this prevents damage to the power switch. the led switching regulator also has built in soft-start. by placing a capacitor from the ss4 pin to gnd, the user can program the soft-start time.
lt1942 11 1942fb applicatio s i for atio wu uu setting the output voltages unlike charge-pump-based tft supplies, the lt1942 tft outputs can all be independently set. the av dd , v off and v on outputs are all inductively based dc/dc converters. as such, the output voltages are set by choosing the right feedback divider ratio. the av dd feedback pin is fb1 and the reference voltage is 1.25v. the v off feedback pin is nfb2 and the reference voltage is 150mv. the v on feedback pin is fb3 and the reference voltage is 1.25v. the led driver is also an inductively based dc/dc converter. output disconnect the v on switching regulator has built in output discon- nect. when the v on supply is enabled, the boost converter will charge up the d3 node. with the output disconnect pnp (q5) turned off, the voltage on v out3 will be zero. once the power sequencing circuitry turns on the pnp, v out3 will go to nearly the same voltage as d3. the v off switching regulator naturally achieves output disconnect due to the switching topology (inverting con- figuration). when the lt1942 is in shutdown, v off will go to zero volts. the av dd switching regulator provides a pgood pin to be used for an external output disconnect function. this pin can drive the gate of a pmos device. when the lt1942 is first enabled, the av dd switching regulator begins to charge up the output capacitor. since pgood is still an open collector at this point, the pmos device is turned off, leaving the av dd output at zero volts. once the output capacitor charges to 97% of the final value, pgood latches low turning on the pmos device and bringing the av dd output quickly to the desired voltage. soft-start the higher current regulators, av dd and led, have user programmable soft-start functions built into the part. simply place a capacitor from the ss1 pin to gnd to achieve soft-start for the av dd switcher. for the led switcher, place a capacitor from the ss4 pin to gnd. a good value for both soft-start capacitors is 0.1 f. the soft-start time is dependent on the load characteristics which will vary depending on the type and size of the tft display. it is a good practice to experiment to determine the best value for the soft-start capacitors. power sequencing the tft supply has integrated supply sequencing built-in to ensure proper initiation of the tft display. figure 1 shows a state diagram of the power sequencing circuitry. the power sequencing circuitry insures that the av dd supply comes up first, then the negative v off supply and lastly the v on positive supply. to pick the ct capacitor for a particular delay, use the following equation: c at v t delay = 10 07 . figure 2 shows the power sequencing during start-up of the tft power supply for the circuit shown in the figure on the first page of this data sheet. all bias supplies start up in a well controlled and well timed manner. the led backlight driver is independently controlled via the ctrl4 pin.
lt1942 12 1942fb applicatio s i for atio wu uu av dd enabled v off disabled v on disabled shutdown i q < 1 a tft supply sequence complete v off enabled v on enabled fb1 > (97% of 1.25v) start v shdn > 1v pgood goes low output disconnect pnp turns on ct timer starts v shdn < 0.4v v ct v be 1942 f01 figure 1. power sequencing state diagram figure 2. power sequencing during tft supply start-up (refer to figure 4 node names) v c1 5v/div v avdd 5v/div v off 10v/div v d3 10v/div v on 10v/div 2ms/div 1942 f02 v shdn 1v/div
lt1942 13 1942fb layout hints proper layout techniques must be followed to achieve advertised performance of the part. keep all sw and fb traces short and small. there are several power ground pins on the lt1942 and it is important to implement the grounding properly. pgnd14 is the power ground pin for the av dd and led switchers. the output capacitor for both the av dd and led switcher must be returned back to this pin before being allowed to mix into the ground plane. similarly, pgnd23 is the power ground pin for the v on and v off switcher. again, both output capacitors for the v on and v off switchers need to return to the pgnd23 pin before mixing with the ground plane. place the input decoupling capacitor, which ties from the v cc pin to gnd, as close to the part as possible. please refer to figure 3 for a recommended layout of the power path components. the component names are those shown in the circuit of figure 4. applicatio s i for atio wu uu v in v in led1 string led2 string led output 1942 f03 c2 l5 c6 c5 c1 d1 l1 c4 l2 l4 l3 c3 v on output gnd plane lt1942 1 v off output av dd output figure 3: power path component recommended layout (refer to figure 4 component names)
lt1942 14 1942fb typical applicatio s u figure 4. tft bias (5v, 10v, ?0v) and white led backlight supply from single li-ion cell ctrl4 sgnd/ agnd d3 sw3 lt1942 sw1 fb1 pgnd14 pgood sw4 d4 led1 led2 fb4 fb3 pgnd23 v out3 nfb2 d2 sw2 c5 0.1 f 16v c6 c2 0.22 f 16v l2 47 h v in l5 47 h shdn v cc ss1 ss4 ct l3 22 h l1 22 h l4 33 h r1 301k d1 r8 1m r2 100k v in 4.7pf m1 pmos c7 0.1 f c9 0.1 f c8 0.1 f 1942 f04a c3 0.22 f 16v c5 2.2 f c1 to c9: x5r or x7r d1: cmdsh-3 central semiconductor l1: 22 h murata lqh32cn220k53 l2, l5: 47 h taiyo yuden lb2012b470 l3: 22 h taiyo yuden lb2012b220 l4: 33 h sumida cdph4d19-330mc m1: si2301bds siliconix shutdown led control av dd 5v 40ma c1 4.7 f 6.3v c4 4.7 f 25v x5r r5 698k r6 100k r4 10k v in 3v to 4.2v v on 10v 2ma v off ?0v 2ma r3 665k r7 4.99 ? 20ma 20ma led control voltage >2.5v 0.25v <0.1v led current 20ma 2.5ma disabled total led current (ma) 5 efficiency (%) 80 85 90 20 30 1942 f04b 75 70 10 15 25 35 40 65 60 v in = 4.2v v in = 3.6v v in = 3v av dd load = 40ma v off load = 2ma v on load = 2ma v avdd 5v/div v off 10v/div v on 10v/div 2ms/div 1942 f04c v shdn 1v/div v avdd 20mv/div ac-coupled i li 50ma/div 100 s/div 1942 f04d efficiency av dd transient response, i load stepped from 30ma 40ma 30ma tft power supply sequencing
lt1942 15 1942fb u package descriptio uf package 24-lead plastic qfn (4mm 4mm) (reference ltc dwg # 05-08-1697) 4.00 0.10 (4 sides) note: 1. drawing proposed to be made a jedec package outline mo-220 variation (wggd-x)?o be approved 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side, if present 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package pin 1 top mark (note 6) 0.38 0.10 24 0.23 typ (4 sides) 23 1 2 bottom view?xposed pad 2.45 0.10 (4-sides) 0.75 0.05 r = 0.115 typ 0.25 0.05 0.50 bsc 0.200 ref 0.00 ?0.05 (uf24) qfn 1103 recommended solder pad pitch and dimensions 0.70 0.05 0.25 0.05 0.50 bsc 2.45 0.05 (4 sides) 3.10 0.05 4.50 0.05 package outline information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
lt1942 16 1942fb linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2004 lt/lt 1106 rev b ? printed in usa related parts part number description comments lt1613 550ma (i sw ), 1.4mhz high efficiency step-up v in : 0.9v to 10v, v out(max) = 34v, i q = 3ma, i sd < 1 a, thinsot package dc/dc converter lt1615/lt1615-1 300ma/80ma (i sw ), constant off-time, high efficiency v in : 1.2v to 15v, v out(max) = 34v, i q = 20 a, i sd < 1 a, step-up dc/dc converter thinsot package lt1930/lt1930a 1a (i sw ), 1.2mhz/2.2mhz high efficiency step-up v in : 2.6v to 16v, v out(max) = 34v, i q = 4.2ma/5.5ma, i sd < 1 a, dc/dc converter thinsot package lt1932 constant current, 1.2mhz, high efficiency white v in : 1v to 10v, v out(max) = 34v, i q = 1.2ma, i sd < 1 a, led boost regulator thinsot package lt1943 (quad) quad output, 2.6a buck, 2.6a boost, 0.3a boost, v in : 4.5v to 22v, v out(max) = 40v, i q = 10ma, i sd < 35 a, 0.4a inverter, 1.2mhz tft dc/dc converter tssop28e package lt1944/lt1944-1 dual output 350ma/100ma (i sw ), constant off-time, v in : 1.2v to 15v, v out(max) = 34v, i q = 20 a, i sd < 1 a, ms10 package (dual) high efficiency step-up dc/dc converter lt1945 dual output, pos/neg, 350ma (i sw ), constant off-time, v in : 1.2v to 15v, v out(max) = 34v, i q = 20 a, i sd < 1 a, ms10 package high efficiency step-up dc/dc converter lt1947 adjustable output tft-lcd triple switching regulator v in : 2.7v to 8v, v out(max) = 30v, i q = 9.5ma, i sd < 1 a, ms10 package ltc3450 triple output power supply for small tft-lcds v in : 1.5v to 4.6v, v out(max) = 15v, i q = 75 a, i sd < 1 a, dfn package lt3461/lt3461a 0.3a (i sw ), 1.3mhz/3mhz, high efficiency step-up v in : 2.5v to 16v, v out(max) = 38v, i q = 2.8ma, i sd < 1 a, dc/dc converter with integrated schottky sc70, thinsot packages lt3464 0.08a (i sw ), high efficiency step-up dc/dc converter v in : 2.3v to 10v, v out(max) = 34v, i q = 25 a, i sd < 1 a, with integrated schottky, output disconnect thinsot package lt3465/lt3465a constant current, 1.2mhz/2.7mhz high efficiency v in : 2.7v to 16v, v out(max) = 34v, i q = 1.9ma, i sd < 1 a, white led boost regulator with integrated schottky thinsot package lt3466 dual constant current, 2mhz, high efficiency white led v in : 2.7v to 24v, v out(max) = 40v, i q = 5ma, i sd < 16 a, dfn package boost regulator with integrated schottky lt3467/lt3467a 1.1a (i sw ), 1.3mhz/2.1mhz, high efficiency step-up v in : 2.4v to 16v, v out(max) = 40v, i q = 1.2ma, i sd < 1 a, dc/dc converter with integrated soft-start thinsot package

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