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1 for more information www.linear.com/LTC3374A typical a pplica t ion fea t ures descrip t ion high accuracy 8-channel parallelable 1a buck dc/dcs the lt c ? 3374a is a multioutput power supply ic consisting of eight synchronous 1a buck converters, all powered from independent 2.25v to 5.5v input supplies. an upgraded pin-compatible version of the ltc3374, the LTC3374A, has higher efficiency, improved output voltage accuracy and an added overvoltage (ov) indicator. the dc/dcs may be used independently or in parallel to achieve higher output currents of up to 4a with a shared inductor. the common buck switching frequency may be programmed with an external resistor, synchronized to an external oscillator, or set to a default internal 2mhz clock. the operating mode for all dc/dcs may be programmed via the mode pin. to reduce input noise the buck converters are phased in 90 steps. precision enable pin thresholds simplify power- up sequencing. the LTC3374A is available in a 38-lead 5mm 7mm qfn package as well as a 38- lead exposed pad tssop package. eight synchronous 1a buck regulators buck efficiency vs i load a pplica t ions n 8-channel 1a independent step-down dc/dcs n master-slave configurable for up to 4a of output current with a single inductor n independent v in supplies for each dc/dc (2.25v to 5.5v) n all dc/dcs have 0.8v to v in output range n 1% v fb accuracy, for buck 1 (1a to 4a) n 1% pgood accuracy n precision enable pin thresholds for autonomous sequencing n 1mhz to 3mhz programmable/synchronizable oscillator frequency (2mhz default) n die temperature monitor output n thermally enhanced 38-lead 5mm 7mm qfn and tssop packages n pin-compatible with ltc3374 n general purpose multichannel power supplies n industrial/automotive/communications l , lt, ltc, ltm, linear technology, the linear logo and burst mode are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. buck 1 0.8v to v in1 up to 1a sw1 2.7v to 5.5v 2.25v to 5.5v 2.25v to 5.5v sw2 v in2 sw8 v in8 fb1 fb2 fb8 v in1 buck 2 0.8v to v in2 up to 1a en2 en8 2.25v to 5.5v en1 buck 8 0.8v to v in8 up to 1a gnd LTC3374A 3374a ta01a ? ? ? ? ? ? pgood_all temp v cc mode sync rt the eight bucks can be configured in 15 different master/slave combinations lt c3374a 3374af 100m 1 4 0 10 20 30 40 50 60 v out = 1.8v 70 80 90 100 efficiency (%) 3374a ta01b f osc = 1mhz v in = 3.3v v out = 1.8v burst mode operation 1a buck, l = 4.7h, l dcr = 40m 2a buck, l = 2.2h, l dcr = 13m 3a buck, l = 1.8h, l dcr = 10m 4a buck, l = 1.0h, l dcr = 8m load current (a) 1m 10m
2 for more information www.linear.com/LTC3374A p in c on f igura t ion a bsolu t e maxi m u m r a t ings v i n1 -8 , fb1 -8, e n1 -8, v cc , pgood_all , sync, rt, temp .......................................... C 0. 3v to 6v mode .................. C 0. 3v to lesser of (v cc + 0.3v ) or 6v i pgood_all ............................................................... 5ma (note 1) 13 14 15 16 top view 39 gnd uhf package 38-lead (5mm 7mm) plastic qfn 17 18 19 38 37 36 35 34 33 32 24 25 26 27 28 29 30 31 8 7 6 5 4 3 2 1fb1 v in1 sw1 sw2 v in2 fb2 fb3 v in3 sw3 sw4 v in4 fb4 fb8 v in8 sw8 sw7 v in7 fb7 fb6 v in6 sw6 sw5 v in5 fb5 en1 en2 temp v cc mode en7 en8 en4 en3 pgood_all sync rt en6 en5 23 22 21 20 9 10 11 12 t jmax = 150c, e ja = 34c/w exposed pad (pin 39) is gnd, must be soldered to pcb 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 top view fe package 38-lead plastic tssop 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 temp en2 en1 fb1 v in1 sw1 sw2 v in2 fb2 fb3 v in3 sw3 sw4 v in4 fb4 en4 en3 pgood_all sync v cc mode en7 en8 fb8 v in8 sw8 sw7 v in7 fb7 fb6 v in6 sw6 sw5 v in5 fb5 en5 en6 rt 39 gnd t jmax = 150c, e ja = 25c/w exposed pad (pin 39) is gnd, must be soldered to pcb o r d er i n f or m a t ion http://www.linear.com/product/LTC3374A#orderinfo lead free finish tape and reel part marking* package description temperature range LTC3374Aeuhf#pbf LTC3374Aeuhf#trpbf 3374a 38-lead (5mm = 7mm) plastic qfn C40c to 125c LTC3374Aiuhf #pbf LTC3374Aiuhf#trpbf 3374a 38-lead (5mm = 7mm) plastic qfn C40c to 125c LTC3374Ahuhf #pbf LTC3374Ahuhf#trpbf 3374a 38-lead (5mm = 7mm) plastic qfn C40c to 150c LTC3374Aefe #pbf LTC3374Aefe#trpbf LTC3374Afe 38-lead plastic tssop C40c to 125c LTC3374Aife #pbf LTC3374Aife#trpbf LTC3374Afe 38-lead plastic tssop C40c to 125c LTC3374Ahfe #pbf LTC3374Ahfe#trpbf LTC3374Afe 38-lead plastic tssop C40c to 150c consult ltc marketing for parts specified with wider operating temperature ranges. *the temperature grade is identified by a label on the shipping container. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. some packages are available in 500 unit reels through designated sales channels with #trmpbf suffix. i sw1-8 ....................................................................... 2. 6a operating junction temperature range (notes 2, 3) ............................................ C 40 c to 150 c storage temperature range .................. C 65 c to 150 c lt c3374a 3374af
3 for more information www.linear.com/LTC3374A the l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at t a = 25c (note 2). v cc = v in1-8 = 3.3v, unless otherwise specified. e lec t rical c harac t eris t ics symbol parameter conditions min typ max units v cc v cc voltage range l 2.7 5.5 v undervoltage lockout (uvlo) threshold on v cc v cc voltage falling v cc voltage rising l l 2.35 2.45 2.45 2.55 2.55 2.65 v v i cc v cc input supply current all switching regulators in shutdown 0 1 a one or more bucks active sync = 0v, all enabled bucks sleeping one buck enabled, not sleeping, sync?=?0v all bucks enabled, not sleeping, sync = 2mhz 45 155 200 75 230 300 a a a f osc internal oscillator frequency v rt = v cc , sync = 0v v rt = v cc , sync = 0v r t = 400k, sync = 0v l l 1.9 1.75 1.85 2 2 2 2.1 2.25 2.15 mhz mhz mhz synchronization frequency t low , t high > 40ns l 1 3 mhz v sync sync level high sync level low l l 1.2 0.4 v v v rt rt servo voltage r t = 400k l 780 800 820 mv 1a buck regulators v in buck input voltage range l 2.25 5.5 v undervoltage lockout (uvlo) threshold on v in v in voltage falling v in voltage rising l l 1.95 2.05 2.05 2.15 2.15 2.25 v v v out buck output voltage range l v fb v in v i vin shutdown input current burst mode ? operation burst mode operation forced continuous mode operation buck in regulation, sleeping buck in regulation, not sleeping, i sw = 0a (note 4) i sw = 0a, v fb = 0v (note 4) 0 20.5 400 400 2 35 550 550 a a a a i lim pmos current limit 1 buck converter (note 5) 2 buck converters combined (note 5) 3 buck converters combined (note 5) 4 buck converters combined (note 5) 1.4 1.8 3.6 5.4 7.2 2.2 a a a a v fb1 feedback regulation voltage buck 1 buck 1 l 796 792 800 800 804 808 mv mv v fb2-8 feedback regulation voltage bucks 2 to 8 l 784 800 816 mv feedback pin leakage current C50 0 50 na maximum duty cycle v fb = 0v l 100 % r pmos pmos on-resistance i sw = 100ma, v in = 5.0v i sw = 100ma, v in = 3.3v 205 245 m m r nmos nmos on-resistance i sw = 100ma, v in = 5.0v i sw = 100ma, v in = 3.3v 125 135 m m pmos leakage current en = 0 C100 0 100 na nmos leakage current en = 0 C100 0 100 na soft-start time (note 6) l 0.25 1.3 3 ms rising pgood threshold voltage buck 1, as a percentage of the regulated v out bucks 2 to 8, as a percentage of the regulated v out l l 97 94 98 95 99 96 % % pgood hysteresis as a per centage of the regulated v out 0.5 1 1.5 % overvoltage indication as a percentage of the regulated v out l 106 107.5 109 % overvoltage hysteresis as a percentage of the regulated v out 2 3 4 % lt c3374a 3374af
4 for more information www.linear.com/LTC3374A the l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at t a = 25c (note 2). v cc = v in1-8 = 3.3v, unless otherwise specified. e lec t rical c harac t eris t ics 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 LTC3374A is tested under pulsed load conditions such that t j t a . the LTC3374Ae is guaranteed to meet specifications from 0c to 85c junction temperature. specifications over the C40c to 125c operating junction temperature range are assured by design, characterization and correlation with statistical process controls. the LTC3374Ai is guaranteed over the C40c to 125c operating junction temperature range and the LTC3374Ah is guaranteed over the C40c to 150c operating junction temperature range. high junction temperatures degrade operating lifetimes; operating lifetime is derated for junction temperatures greater than 125c. note that the maximum ambient temperature consistent with these specifications is determined by specific operating conditions in conjunction with board layout, the rated package thermal impedance, and other environmental factors. the junction temperature (t j in c) is calculated from ambient temperature (t a in c) and power dissipation (p d in watts) according to the formula: t j = t a + (p d ? ja ) where ja (in c/w) is the package thermal impedance. symbol parameter conditions min typ max units temperature monitor v temp temp voltage at 25c v temp slope 200 220 7 240 mv mv/ c ot overtemperature shutdown (note 3) temperature rising hysteresis 170 10 c c interface logic pins i oh output high leakage current 5.5v at the pgood_all pin C1 0 1 a v ol output low voltage 3ma into the pgood_all pin 0.1 0.4 v v ih input high threshold mode pin l 1.2 v v il input low threshold mode pin l 0.4 v i ih input high leakage current mode, en 1-8 C100 0 100 na i il input low leakage current mode, en 1-8 C100 0 100 na en rising threshold first regulator turning on one regulator already in use l l 400 380 730 400 1200 420 mv mv en falling threshold l 300 320 340 mv note 3: the LTC3374A includes overtemperature protection which protects the device during momentary overload conditions. junction temperatures will exceed 150c when overtemperature protection is active. continuous operation above the specified maximum operating junction temperature may impair device reliability. note 4: static current, switches not switching. actual current may be higher due to gate charge losses at the switching frequency. note 5: the current limit features of this part are intended to protect the ic from short term or intermittent fault conditions. continuous operation above the maximum specified pin current rating may result in device degradation over time. note 6: the soft-start time is the time from the start of switching until the fb pin reaches 775mv. when a buck is enabled there is a 100s (typical) delay before switching commences. lt c3374a 3374af
5 for more information www.linear.com/LTC3374A typical p er f or m ance c harac t eris t ics v cc quiescent current vs temperature v cc quiescent current vs temperature rt programmed oscillator frequency vs temperature default oscillator frequency vs temperature oscillator frequency vs v cc v cc undervoltage threshold vs temperature buck v in undervoltage threshold vs temperature v cc quiescent current vs temperature v cc = 2.7v v cc = 3.3v v cc = 5.5v v cc = 2.7v v cc = 3.3v v cc = 5.5v v cc = 2.7v v cc = 3.3v v cc = 5.5v v cc = 2.7v v cc = 3.3v v cc = 5.5v v cc = 2.7v v cc = 3.3v v cc = 5.5v t a = 25c, unless otherwise noted. lt c3374a 3374af 75 2.00 2.05 2.10 2.15 2.20 f osc (mhz) 3374a g06 temperature (c) ?50 ?25 100 0 25 50 75 100 125 150 1.80 1.85 1.90 125 1.95 2.00 2.05 2.10 2.15 2.20 f osc (mhz) 3374a g07 r t = 400k v rt = v cc 150 v cc (v) 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 1.80 2.35 1.85 1.90 1.95 2.00 2.05 2.10 2.15 2.20 f osc (mhz) 3374a g08 2.40 temperature (c) ?50 ?25 0 25 50 75 100 125 150 2.45 0 50 100 150 200 250 300 350 400 i vcc (a) 2.50 3374a g05 all bucks enabled, not sleeping sync = 2mhz 2.55 2.60 v cc rising 2.65 uv threshold (v) 3374a g01 v in rising v in falling temperature (c) ?50 ?25 0 25 v cc falling 50 75 100 125 150 1.95 2.00 2.05 2.10 2.15 temperature (c) 2.20 2.25 uv threshold (v) 3374a g02 all enabled bucks sleeping temperature (c) ?50 ?25 0 25 ?50 50 75 100 125 150 0 20 40 60 80 ?25 100 i vcc (a) 3374a g03 one buck enabled, not sleeping sync = 0v temperature (c) ?50 ?25 0 25 50 0 75 100 125 150 0 50 100 150 200 250 25 300 350 400 i vcc (a) 3374a g04 r t = 400k temperature (c) ?50 ?25 0 50 25 50 75 100 125 150 1.80 1.85 1.90 1.95
6 for more information www.linear.com/LTC3374A oscillator frequency vs r t en pin rising threshold vs temperature v temp vs temperature typical p er f or m ance c harac t eris t ics en pin falling threshold vs temperature buck v in quiescent current vs temperature buck v in quiescent current vs temperature v fb vs temperature en pin rising threshold vs temperature r t (k) 250 f osc (mhz) 2.0 2.5 3.0 650 750700 3374a g09 1.5 1.0 0 350 450 550 300 800 400 500 600 0.5 4.0 3.5 v cc = 3.3v v in = 2.25v v in = 3.3v v in = 5.5v v in = 2.25v v in = 3.3v v in = 5.5v pmos current limit vs temperature v in = 2.25v v in = 3.3v v in = 5.5v t a = 25c, unless otherwise noted. lt c3374a 3374af 75 10 20 30 40 50 i vin (a) 3374a g14 burst mode operation fb = 850mv v in = 3.3v temperature (c) 100 ?50 ?25 0 25 50 75 100 125 150 1.4 125 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 i lim (a) 3374a g17 150 temperature (c) ?50 ?25 0 25 50 75 100 125 150 ?200 0 50 100 150 200 250 300 350 400 450 0 500 550 i vin (a) 3374a g15 forced continuous mode fb = 0v temperature (c) ?50 ?25 0 25 200 50 75 100 125 150 792 794 796 798 800 400 802 804 806 808 v fb (mv) 3374a g16 600 800 ideal v temp 1000 1200 v temp (mv) 3374a g10 first buck turning on temperature (c) ?50 ?25 0 25 actual v temp 50 75 100 125 150 500 550 600 650 700 temperature (c) 750 800 850 900 en threshold (mv) 3374a g11 one buck already enabled temperature (c) ?50 ?25 ?50 0 25 50 75 100 125 150 380 385 390 ?25 395 400 405 410 415 420 en threshold (mv) 3374a g12 temperature (c) ?50 0 ?25 0 25 50 75 100 125 150 300 305 25 310 315 320 325 330 335 340 en threshold (mv) 3374a g13 temperature (c) 50 ?50 ?25 0 25 50 75 100 125 150 0
7 for more information www.linear.com/LTC3374A typical p er f or m ance c harac t eris t ics 1a buck efficiency vs i load, v out ?=?3.3v 2a buck efficiency vs i load, v out ?=?1.2v 2a buck efficiency vs i load, v out ?=?1.8v 2a buck efficiency vs i load, v out ?=?2.5v 1a buck efficiency vs i load, v out? =?1.2v 1a buck efficiency vs i load, v out ?=?1.8v 1a buck efficiency vs i load, v out ?=?2.5v pmos r ds(on) vs temperature nmos r ds(on) vs temperature t a = 25c, unless otherwise noted. v in = 2.25v v in = 3.3v v in = 5.5v v in = 2.25v v in = 3.3v v in = 5.5v lt c3374a 3374af load current (a) 60 70 80 90 100 efficiency (%) 3374a g23 burst mode operation forced continuous mode v in = 2.25v 1m v in = 3.3v v in = 5.5v v in = 2.25v v in = 3.3v v in = 5.5v l = 1.0h l dcr = 13m f osc = 2mhz load current (a) burst mode operation 1m 10m 10m 100m 1 2 0 10 20 30 40 50 60 100m 70 80 90 100 efficiency (%) 3374a g24 forced continuous mode v in = 2.8v v in = 3.3v v in = 5.5v 1 v in = 2.8v v in = 3.3v v in = 5.5v load current (a) 1m 10m 100m 1 2 0 0 10 20 30 40 50 60 70 80 90 100 10 efficiency (%) 3374a g26 l = 1.0h l dcr = 13m f osc = 2mhz burst mode operation i pmos = 100ma temperature (c) ?50 ?25 0 25 20 50 75 100 125 150 150 200 250 300 350 30 400 450 resistance (m) 3374a g18 i nmos = 100ma temperature (c) ?50 ?25 0 25 40 50 75 100 125 150 75 100 125 150 175 forced continuous mode 50 200 225 250 resistance (m) 3374a g19 forced continuous mode v in = 2.5v v in = 3.3v v in = 5.5v v in = 2.5v 60 v in = 3.3v v in = 5.5v l = 1.0h l dcr = 13m f osc = 2mhz load current (a) 1m 10m 100m 1 2 0 70 10 20 30 40 50 60 70 80 90 100 80 efficiency (%) 3374a g25 burst mode operation 90 100 efficiency (%) 3374a g20 burst mode operation forced continuous mode v in = 2.25v v in = 2.5v v in = 3.3v v in = 5.5v v in = 2.5v v in = 3.3v v in = 5.5v l = 2.2h l dcr = 21m f osc = 2mhz load current (a) 1m 10m v in = 3.3v 100m 1 0 10 20 30 40 50 60 70 v in = 5.5v 80 90 100 efficiency (%) 3374a g21 burst mode operation forced continuous mode v in = 2.8v v in = 3.3v v in = 5.5v v in = 2.25v v in = 2.8v v in = 3.3v v in = 5.5v l = 2.2h l dcr = 21m f osc = 2mhz burst mode operation load current (a) 1m 10m 100m 1 v in = 3.3v 0 10 20 30 40 50 60 70 80 90 v in = 5.5v 100 efficiency (%) 3374a g22 forced continuous mode v in = 4.2v v in = 5.5v v in = 4.2v v in = 5.5v l = 2.2h l dcr = 21m f osc = 2mhz load current (a) l = 2.2h l dcr = 21m f osc = 2mhz 1m 10m 100m 1 0 10 20 30 40 50
8 for more information www.linear.com/LTC3374A 4a buck efficiency vs i load, v out ?=?1.2v 4a buck efficiency vs i load, v out ?=?1.8v 4a buck efficiency vs i load, v out ?=?2.5v 1a buck efficiency vs frequency (forced continuous mode) typical p er f or m ance c harac t eris t ics 1a buck efficiency vs frequency (forced continuous mode) 1a buck efficiency vs i load (across operating frequency) t a = 25c, unless otherwise noted. 3a buck efficiency vs i load, v out ?=?1.2v 3a buck efficiency vs i load, v out ?=?1.8v 3a buck efficiency vs i load, v out ?=?2.5v lt c3374a 3374af load current (a) 2.2 2.4 2.6 2.8 3.0 0 10 20 30 40 1m 50 60 70 80 90 100 efficiency (%) 3374a g33 v out = 1.8v l = 3.3h 10m v in = 3.3v i load = 100ma i load = 500ma i load = 20ma frequency (mhz) 1 1.2 1.4 1.6 1.8 100m 2.0 2.2 2.4 2.6 2.8 3.0 0 10 20 30 1 40 50 60 70 80 90 100 efficiency (%) 3374a g34 forced continuous mode 4 f osc = 1mhz, l = 3.3h f osc = 2mhz, l = 2.2h f osc = 3mhz, l = 1.0h f osc = 1mhz, l = 3.3h f osc = 2mhz, l = 2.2h f osc = 3mhz, l = 1.0h load current (a) 1m 10m 100m 0 1 0 10 20 30 40 50 60 70 80 10 90 100 efficiency (%) 3374a g35 v in = 3.3v, v out = 1.8v burst mode operation forced continuous mode v in = 2.25v v in = 3.3v v in = 5.5v 20 v in = 2.25v v in = 3.3v v in = 5.5v l = 0.8h l dcr = 5m f osc = 2mhz load current (a) 1m 10m 100m 1 3 30 0 10 20 30 40 50 60 70 80 90 forced continuous mode 40 100 efficiency (%) 3374a g27 burst mode operation forced continuous mode v in = 2.5v v in = 3.3v v in = 5.5v v in = 2.5v v in = 3.3v 50 v in = 5.5v l = 0.8h l dcr = 5m f osc = 2mhz load current (a) 1m 10m 100m 1 3 0 10 60 20 30 40 50 60 70 80 90 100 efficiency (%) 70 3374a g28 burst mode operation forced continuous mode v in = 2.8v v in = 3.3v v in = 5.5v v in = 2.8v v in = 3.3v v in = 5.5v l = 0.8h l dcr = 5m f osc = 2mhz 80 load current (a) 1m 10m 100m 1 3 0 10 20 30 90 40 50 60 70 80 90 100 efficiency (%) 3374a g29 burst mode operation 100 efficiency (%) 3374a g30 burst mode operation v in = 2.25v forced continuous mode l = 0.6h l dcr = 4m f osc = 2mhz v in = 2.5v v in = 3.3v v in = 5.5v v in = 2.5v v in = 3.3v v in = 5.5v load current (a) 1m v in = 3.3v 10m 100m 1 4 0 10 20 30 40 50 v in = 5.5v 60 70 80 90 100 efficiency (%) 3374a g31 burst mode operation forced continuous mode burst mode v in = 2.25v v in = 2.8v v in = 3.3v v in = 5.5v v in = 2.8v v in = 3.3v v in = 5.5v load current (a) 1m 10m 100m v in = 3.3v 1 4 0 10 20 30 40 50 60 70 v in = 5.5v 80 90 100 efficiency (%) 3374a g32 burst mode operation l = 0.6h l dcr = 4m f osc = 2mhz v out = 1.8v l = 3.3h i load = 100ma l = 0.6h l dcr = 4m f osc = 2mhz v in = 2.25v v in = 3.3v v in = 5.5v frequency (mhz) 1 1.2 1.4 1.6 1.8 2.0
9 for more information www.linear.com/LTC3374A 1a buck regulator load regulation (forced continuous mode) 4a buck regulator load regulation (forced continuous mode) 1a buck regulator line regulation (forced continuous mode) f osc = 2mhz l = 2.2h v in = 2.25v v in = 3.3v v in = 5.5v f osc = 2mhz l = 2.2h v in = 2.25v v in = 3.3v v in = 5.5v f osc = 2mhz l = 2.2h i load = 1ma i load = 500ma typical p er f or m ance c harac t eris t ics 1a buck regulator, transient response (forced continuous mode) 4a buck regulator, transient response (forced continuous mode) 4a buck regulator, transient response (burst mode operation) 40s/div v out 100mv/div ac-coupled inductor current 250ma/div 3374a g42 load step: 100ma to 700ma v in = 3.3v l = 2.2h v out = 1.8v 0ma 40s/div v out 100mv/div ac-coupled inductor current 1a/div 3374a g43 load step: 400ma to 2.8a v in = 3.3v l = 0.6h v out = 1.8v 0a 40s/div 0a v out 100mv/div ac-coupled inductor current 1a/div 3374a g44 load step: 400ma to 2.8a v in = 3.3v l = 0.6h v out = 1.8v 1a buck regulator no-load start-up transient 4a buck regulator no-load start-up transient 1a buck regulator, transient response (burst mode operation) 400s/div v out 500mv/div inductor current 250ma/div 3374a g39 v in = 3.3v l = 2.2h 0ma en 2v/div 0v 0v 400s/div v out 500mv/div inductor current 2a/div 3374a g40 v in = 3.3v l = 0.6h en 2v/div 0a 0v 0v 40s/div v out 100mv/div ac-coupled inductor current 250ma/div 3374a g41 load step: 100ma to 700ma v in = 3.3v l = 2.2h v out = 1.8v 0ma t a = 25c, unless otherwise noted. lt c3374a 3374af 1.790 1.795 1.800 1.805 1.810 1.815 1.820 v out (v) 3374a g36 dropout dropout load current (a) 1m 10m 100m 1 4 1.780 1.785 1.790 1.795 load current (a) 1.800 1.805 1.810 1.815 1.820 v out (v) 3374a g37 v in (v) 2 2.5 1m 3 3.5 4 4.5 5 5.5 1.780 1.785 1.790 1.795 10m 1.800 1.805 1.810 1.815 1.820 v out (v) 3374a g38 100m 1 1.780 1.785
10 for more information www.linear.com/LTC3374A p in func t ions (qfn/tssop) fb1 (pin 1/pin 4): feedback pin for buck regulator 1. program the output voltage and close the control loop by connecting this pin to the middle node of a resistor divider between the output and ground. v in1 (pin 2/pin 5): buck regulator 1 input supply. bypass to gnd with a 10f or larger ceramic capacitor. sw1 (pin 3/pin 6): switch node for buck regulator 1. connect an external inductor to this pin. sw2 (pin 4/pin 7): switch node for buck regulator 2. connect an external inductor to this pin. v in2 (pin 5/pin 8): buck regulator 2 input supply. bypass to gnd with a 10f or larger ceramic capacitor. short to v in1 when buck regulator 2 is combined with buck regula - tor 1 for higher current. fb2 (pin 6/pin 9) : feedback pin for buck regulator 2. program the output voltage and close the control loop by connecting this pin to the middle node of a resistor divider between the output and ground. to combine buck regulator 2 with buck regulator 1 for higher current, connect fb2 to v in2 . up to four converters may be combined in this way. fb3 (pin 7/pin 10): feedback pin for buck regulator 3. program the output voltage and close the control loop by connecting this pin to the middle node of a resistor divider between the output and ground. t o combine buck regula - tor? 3 with buck regulator 2 for higher current, connect fb3 to v i n3 . up to four converters may be combined in this way. v i n3 (pin 8/pin 11): buck regulator 3 input supply. bypass to gnd with a 10f or larger ceramic capacitor. short to v in2 when buck regulator 3 is combined with buck regula - tor 2 for higher current. sw3 (pin 9/pin 12) : switch node for buck regulator 3. connect an external inductor to this pin. sw4 (pin 10/pin 13): switch node for buck regulator 4. connect an external inductor to this pin. v in4 (pin 11/pin 14): buck regulator 4 input supply. bypass to gnd with a 10f or larger ceramic capacitor. short to v in3 when buck regulator 4 is combined with buck regulator 3 for higher current. fb4 (pin 12/pin 15): feedback pin for buck regulator 4. program the output voltage and close the control loop by connecting this pin to the middle node of a resistor divider between the output and ground. to combine buck regula - tor?4 with buck regulator 3 for higher current, connect fb4 to v i n4 . up to four converters may be combined in this way. en4 (pin 13/pin 16): enable input for buck regulator 4. active high. do not float. e n3 (pin 14/pin 17): enable input for buck regulator 3. active high. do not float. pgood_all (pin 15/pin 18) : pgood status pin. open- drain output. when the regulated output voltage of any enabled switching regulator falls below its pgood threshold or rises above its overvoltage threshold, this pin is driven low. when all buck regulators are disabled pgood_all is driven low. sync (pin 16/pin 19): oscillator synchronization pin. driving sync with an external clock signal synchronizes all switchers to the applied frequency. the slope com - pensation is automatically adapted to the external clock frequency . the absence of an external clock signal enables the frequency programmed by the rt pin. sync should be held at ground if not used. do not float. rt (pin 17/pin 20) : oscillator frequency pin. connect a resistor from rt to ground to program the switching frequency. tie rt to v cc to use the default internal 2mhz oscillator. do not float. en6 (pin 18/pin 21): enable input for buck regulator 6. active high. do not float. en5 (pin 19/pin 22): enable input for buck regulator 5. active high. do not float. fb5 (pin 20/pin 23): feedback pin for buck regulator 5. program the output voltage and close the control loop by connecting this pin to the middle node of a resistor divider between the output and ground. to combine buck regula - tor?5 with buck regulator 4 for higher current, connect fb5 to v i n5 . up to four converters may be combined in this way. lt c3374a 3374af
11 for more information www.linear.com/LTC3374A p in func t ions (qfn/tssop) v in5 (pin 21/pin 24): buck regulator 5 input supply. bypass to gnd with a 10f or larger ceramic capacitor. short to v in4 when buck regulator? 5 is combined with buck regulator 4 for higher current. sw5 (pin 22/pin 25): switch node for buck regulator 5. connect an external inductor to this pin. sw6 (pin 23/pin 26): switch node for buck regulator 6. connect an external inductor to this pin. v in6 (pin 24/pin 27): buck regulator 6 input supply. bypass to gnd with a 10f or larger ceramic capacitor. short to v in5 when buck regulator 6 is combined with buck regulator 5 for higher current. fb6 (pin 25/pin 28): feedback pin for buck regulator 6. program the output voltage and close the control loop by connecting this pin to the middle node of a resistor divider between the output and ground. to combine buck regula - tor?6 with buck regulator 5 for higher current, connect fb6 to v i n6 . up to four converters may be combined in this way. fb7 (pin 26/pin 29): feedback pin for buck regulator?7. program the output voltage and close the control loop by connecting this pin to the middle node of a resistor divider between the output and ground. to combine buck regula - tor?7 with buck regulator 6 for higher current, connect fb7 to v i n7 . up to four converters may be combined in this way. v in7 (pin 27/pin 30): buck regulator 7 input supply. bypass to gnd with a 10f or larger ceramic capacitor. short to v in6 when buck regulator? 7 is combined with buck regulator 6 for higher current. sw7 (pin 28/pin 31): switch node for buck regulator 7. connect an external inductor to this pin. sw8 (pin 29/pin 32): switch node for buck regulator 8. connect an external inductor to this pin. v in8 (pin 30/pin 33): buck regulator 8 input supply. bypass to gnd with a 10f or larger ceramic capacitor. short to v in7 when buck regulator 8 is combined with buck regulator 7 for higher current. fb8 (pin 31/pin 34): feedback pin for buck regulator?8. program the output voltage and close the control loop by connecting this pin to the middle node of a resistor divider between the output and ground. to combine buck regula - tor?8 with buck regulator?7 for higher current, connect fb8 to v i n8 . up to four converters may be combined in this way. en8 (pin 32/pin 35): enable input for buck regulator 8. active high. do not float. en7 (pin 33/pin 36): enable input for buck regulator 7. active high. do not float. mode (pin 34/pin 37): mode selection logic input. programs burst mode functionality for all buck switch - ing regulators when the pin is set low. when the pin is set high, all buck switching regulators operate in for ced continuous mode. v cc (pin 35/pin 38): internal bias supply. bypass to gnd with a 10f or larger ceramic capacitor. temp (pin 36/pin 1): temperature indication pin. temp outputs a voltage of 220mv (typical) at 25c. the temp voltage changes by 7mv/c (typical) giving an external indication of the ltc3374 a internal die temperature. tie temp to v cc to disable the temperature monitor and save 12a (typical) of quiescent current on v cc . en2 (pin 37/pin 2): enable input for buck regulator 2. active high. do not float. e n1 (pin 38/pin 3): enable input for buck regulator 1. active high. do not float. gnd (exposed pad pin 39/exposed pad pin 39) : ground. the exposed pad must be connected to a continuous ground plane on the printed circuit board directly under the ltc3374 a for electrical contact and rated thermal performance. lt c3374a 3374af
12 for more information www.linear.com/LTC3374A b lock diagra m (pin numbers denote qfn package) 13 39 en4 12 fb4 10 sw4 11 v in4 14 en3 7 fb3 9 sw3 8 v in3 37 en2 6 fb2 4 sw2 master/slave lines master/slave lines master/slave lines master/slave lines gnd (exposed pad) master/slave lines master/slave lines master/slave lines 5 v in2 38 en1 1 fb1 3 sw1 clk 8 pgood 2 19 20 22 21 18 25 23 24 33 26 28 27 32 31 29 30 v in1 en5 3374a bd fb5 sw5 v in5 en6 fb6 sw6 v in6 en7 fb7 sw7 v in7 en8 fb8 sw8 v in8 36 temp pgood_all buck regulator 4 1a buck regulator 3 1a buck regulator 2 1a buck regulator 1 1a buck regulator 5 1a buck regulator 6 1a buck regulator 7 1a buck regulator 8 1a pgood logic 17 rt 16 sync 34 mode 35 v cc 15 clk ref mode sd pgood clk ref mode sd pgood clk ref mode sd pgood clk ref mode sd pgood clk ref mode sd pgood clk ref mode sd pgood clk ref mode sd pgood clk ref mode sd pgood bandgap oscillator uvlo temp monitor ref 8 ot uv sd lt c3374a 3374af
13 for more information www.linear.com/LTC3374A o pera t ion buck switching regulators the ltc3374 a is an upgraded, pin-compatible version of the ltc3374 with higher efficiency and improved accuracy. the major differences between them are outlined in table 1. the LTC3374A contains eight 1a monolithic peak current mode controlled synchronous buck switching regulators. all of the switching regula - tors are internally compensated and need only external feedback resistors to set the output voltage. the switch - ing regulators offer two operating modes: burst mode operation (when the mode pin is set low) for higher efficiency at light loads and forced continuous pwm mode (when the mode pin is set high) for lower noise at light loads. the mode pin collectively sets the operating mode for all enabled buck switching regulators. in burst mode operation at light loads, the output capacitor is charged to a voltage slightly higher than its regulation point. the regulator then goes into a sleep state, during which time the output capacitor provides the load current. in sleep most of the regulator s circuitry is powered down, helping conserve input power. when the output capaci - tor droops below its programmed value, the circuitry is powered on and another burst cycle begins. the sleep time decreases as load current increases. in burst mode operation, the regulator will burst at light loads whereas at higher loads it will operate in constant frequency p wm mode. in forced continuous mode, the oscillator runs continu - ously and the buck switch currents are allowed to reverse under light load conditions to maintain regulation. this mode allows the buck to run at a fixed frequency with minimal output ripple. each buck switching regulator has its own v in , sw, fb and en pins to maximize flexibility. the enable pins have two different enable threshold voltages depending on the operating state of the LTC3374A. with all regulators dis - abled, the enable pin threshold is set to 730mv (typical). once any regulator is enabled, the enable pin thresholds of the remaining regulators are set to a bandgap-based 400mv and the en pins are each monitored by a precision comparator . this precision en threshold may be used to provide event-based power-up sequencing by connect - ing the enable pin to the output of another buck through a resistor divider. all buck regulators have forward and reverse-current limiting, soft-start to limit inrush current during start-up, and short-circuit protection. when a buck is enabled there is a 100s (typical) delay before switching commences and the soft start ramp begins. if a buck is the first one to be enabled there is an additional 1.5ms delay. the buck switching regulators are phased in 90 steps to reduce noise and input ripple. the phase step determines the fixed edge of the switching sequence, which is when the pmos turns on. the pmos off (nmos on) phase is subject to the duty cycle demanded by the regulator. bucks 1 and 2 are set to 0 , bucks 3 and 4 are set to 90, bucks 5 and 6 are set to 180, and bucks 7 and 8 are set to 270. in shutdown all sw nodes are high impedance. table 1. LTC3374A vs ltc3374 feature LTC3374A ltc3374 buck power stages 8 8 buck 1 accuracy* 1% 2.5% bucks 2-8 accuracy* 2% 2.5% pgood buck 1 98% 92.5% pgood buck 2 95% 92.5% ov indication 107.5% - i vcc , shutdown 0a 8a *over temperature lt c3374a 3374af
14 for more information www.linear.com/LTC3374A buck regulators with combined power stages up to four adjacent buck regulators may be combined in a master-slave configuration by connecting their sw pins together, connecting their v in pins together, and connecting the higher numbered bucks fb pin(s) to the input supply. the lowest numbered buck is always the master. in figure?1, buck regulator 1 is the master. the feedback network connected to the fb1 pin programs the output voltage to 1.2v. the fb2 pin is tied to v in , which configures buck regulator 2 as the slave. the sw1 and sw2 pins must be tied together, as must the v in1 and v in2 pins. the slave buck control circuitry draws no dc quiescent current. the enable of the master buck (e n1) controls the operation of the combined bucks; the enable of the slave buck (en2) must be tied to ground. any combination of 2, 3, or 4 adjacent buck regulators may be combined to provide up to 2a, 3a or 4a of output load current, respectively. for example, buck regulator 1 and buck regulator 2 may run independently, while buck regulators 3 and 4 may be combined to provide 2a, while buck regulators 5 through 8 may be combined to provide 4a. buck regulator 1 is never a slave, and buck regulator 8 is never a master. fifteen unique output power stage con - figurations are possible to maximize application flexibility. o pera t ion power failure reporting via pgood_all pin power failure conditions are reported back via the pgood_all pin. all buck switching regulators have an internal power good (pgood) signal. when the regu - lated output voltage of an enabled switcher rises above 98% of its programmed value for buck 1 or 95% for bucks 2 through 8, the pgood signal transitions high. if the regulated output voltage subsequently falls below 97% of the programmed value for buck 1 or 94% for bucks 2 through 8, the pgood signal is pulled low. if any internal pgood signal stays low for greater than 100s, then the pgood_all pin is pulled low, indicating to a microprocessor that a power failure fault has occurred. the 100s filter time prevents the pin from being pulled low during a load transient. in addition, whenever pgood transitions high there will be a 100s assertion delay. the ltc3374 a also reports overvoltage conditions at the pgood_all pin. if any enabled buck regulators output voltage rises above 107.5% of the programmed value, the pgood_all pin is pulled low after 100s . similarly, if all enabled outputs that are overvoltage subsequently fall below 104.5% of the programmed value, the pgood_all pin transitions high again after 100s. an error condition that pulls the pgood_all pin low is not latched. when the error condition goes away, the pgood_all pin is released and is pulled high if no other error condition exists. pgood_all is also pulled low in the following scenarios: if no buck switching regulators are enabled, if any enabled buck is in uvlo, if the v cc supply is in uvlo, or if the LTC3374A is in ot (see below). temperature monitoring and overtemperature protection to prevent thermal damage to the LTC3374A and its surrounding components, the LTC3374A incorporates an overtemperature (ot) function. when the LTC3374A die temperature reaches 170c (typical) all enabled buck switching regulators are shut down and remain in shutdown until the die temperature falls to 160c (typical). figure 1. buck regulators configured as master-slave buck regulator 1 (master) v in v in v in sw1 c out v out 1.2v 2a 400k l1 800k fb1 en1 buck regulator 2 (slave) sw2 en2 v in1 v in2 fb2 3374a f01 lt c3374a 3374af
15 for more information www.linear.com/LTC3374A o pera t ion the die temperature may be read by sampling the analog temp pin voltage. the temperature, t, indicated by the temp pin voltage is given by: t = v temp C 45mv 7mv ? 1c (1) the typical voltage at the temp pin is 220mv at 25c and is valid for die temperatures higher than 25c. if tempera - ture monitoring functionality is not needed, then the user may shut down the temperature monitor in order to lower quiescent current (by 12a typical) by tying temp to v cc . in this case all enabled buck switching regulators are still shut down when the die temperature reaches 170c (typi - cal) and remain in shutdown until the die temperature falls to 160c (typical). if none of the buck switching regula - tors are enabled, the temperature monitor is shut down to further reduce quiescent current. programming the operating frequency selection of the operating frequency is a trade-off between efficiency and component size. high frequency operation allows the use of smaller inductor and capacitor values. operation at lower frequencies improves efficiency by reducing internal gate charge losses but requires larger inductance values and/or capacitance to maintain low output voltage ripple. the operating frequency for all of the ltc3374 a regulators is determined by an external resistor that is connected between the rt pin and ground. the operating frequency is calculated using the following equation: f osc = 2mhz 400k r t ? ? ? ? ? ? (2) while the ltc3374 a is designed to function with operating frequencies between 1mhz and 3mhz , it has safety clamps that prevent the oscillator from running faster than 4mhz (typical) or slower than 250khz (typical). tying the rt pin to v cc sets the oscillator to the default internal operating frequency of 2mhz (typical). the LTC3374A s internal oscillator can alternatively be synchronized through an internal pll circuit to an exter - nal frequency by applying a square wave clock signal to the sync pin. during synchronization, the top mosfet turn-on of buck switching regulators 1 and 2 are locked to the rising edge of the external frequency sour ce. all other buck switching regulators are locked to the appro - priate phase of the external frequency sour ce (see buck switching regulators). while syncing, the buck switching regulators operate in for ced continuous mode, even if the mode pin is low. the synchronization frequency range is 1mhz to 3mhz. after detecting an external clock on the first rising edge of the sync pin, the internal pll starts up at the current frequency being programmed by the rt pin. the internal pll then requires a certain number of periods to gradually adjust its operating frequency to match the frequency and phase of the sync signal. when the external clock is removed the LTC3374A needs approximately 5s to detect the absence of the external clock. during this time, the pll will continue to provide clock cycles before it recognizes the lack of a sync input. once the external clock removal has been identified, the oscillator will gradually adjust its operating frequency to match the desired frequency programmed at the rt pin. sync should be connected to ground if not used. lt c3374a 3374af
16 for more information www.linear.com/LTC3374A a pplica t ions i n f or m a t ion buck switching regulator output voltage and feedback network the output voltage of the buck switching regulators is programmed by a resistor divider connected from the switching regulator s output to its feedback pin and is given by v out = v fb (1 + r2/r1) as shown in figure 2. typical values for r1 range from 40k to 1m. the buck regulator transient response may improve with an optional capacitor c ff that helps cancel the pole created by the feedback resistors and the input capacitance of the fb pin. experimentation with capacitor values between 2pf and 22pf may improve transient response. figure 2. feedback components buck switching regulator v out c out (optional) c ff r2 r1 fb 3374a f02 + input and output decoupling capacitor selection the ltc3374 a has individual input supply pins for each buck switching regulator and a separate v cc pin that supplies power to all top level control and logic. each of these pins must be decoupled with low esr capacitors to gnd. these capacitors should be placed as close to the pins as possible. ceramic dielectric capacitors are a good compromise between high dielectric constant and stability versus temperature and dc bias. note that the capacitance of a capacitor deteriorates at higher dc bias. it is important to consult manufacturer data sheets to obtain the true capacitance of a capacitor at the operating dc bias voltage. for this reason, avoid the use of y5v dielectric capacitors. the x5r/x7r dielectric capacitors offer good overall performance. v cc , pin 35/38, and the input supply voltage pins 2/5, 5/8, 8/11, 11/14, 21/24, 24/27, 27/30, and 30/33 (qfn/ tssop packages) all need to be decoupled with at least 10f capacitors. additionally, all buck regulator outputs should be bypassed with at least 22f to ground for the 1a configuration. combined buck regulators a single 2a buck regulator can be made by combining two adjacent 1a buck regulators together. likewise a 3a or 4a buck regulator can be made by combining any three or four adjacent buck regulators, respectively. tables 3, 4 and?5 show recommended inductors for these configurations. for a 2a combined buck regulator, the input supply should be decoupled with a 22f capacitor and the output should be decoupled with a 47f capacitor. similarly, for 3a and 4a configurations, the input and output capacitance should be scaled up to account for the increased load. refer to the capacitor selection section for details on selecting a proper capacitor. the efficiency of a buck at a given load current may be higher if another buck is combined with it. the combined buck operates at the same load current and that point on its efficiency curve may be higher than that of the single buck. for example, a buck running at a 900ma load may have higher efficiency when two bucks are combined to make a 2a buck, as the 900ma load will be closer to the peak efficiency point of the 2a buck than it was for the 1a buck. it is therefore a good idea to explore combining any unused buck with active bucks in a given application. otherwise, any unused buck regulator should have it s fb and en pins tied to ground. the v in pin may be tied to ground and the sw pin can float. buck regulators all eight buck regulators are optimized to be used with a 2.2h inductor in the 1a, 2mhz configuration. for opera - tion at different frequencies, the inductor value should be scaled inversely proportional to the switching frequency . for combined buck regulators, the inductor value should also be scaled inversely proportional to the number of combined stages. for example, both a 1a buck running at 2mhz and a 2a buck running at 1mhz should use a 2.2h inductor. choose the nearest standard value inductor for the desired configuration. scaling the inductor for differ - ent configurations maintains good transient response. t ables? 2,?3,?4 and 5 show recommended inductor values for the different configurations. lt c3374a 3374af
17 for more information www.linear.com/LTC3374A a pplica t ions i n f or m a t ion table 2. recommended inductors for 1a buck regulators f osc part number l (h) max i dc (a) max dcr (m) size in mm (l w h) manufacturer 1mhz xfl4020-472me 4.7 2.7 57.4 4 4 2.1 coilcraft 74408943047 4.7 2.2 52 4.8 4.8 3.8 wurth elektronik 2mhz xfl4020-222me 2.2 3.7 23.5 4 4 2.1 coilcraft dfe252012p-2r2m 2.2 2.2 84 2.5 2.0 1.2 toko ihlp1212bzer2r2m-11 2.2 3 46 3 3.65 2.0 vishay 3mhz 74438336015 1.5 3.7 39 3 3 2 wurth elektronik dfe252012f-1r5m 1.5 2.7 58 2.5 2 1.2 toko table 3. recommended inductors for 2a buck regulators f osc part number l (h) max i dc (a) max dcr (m) size in mm (l w h) manufacturer 1mhz xel4020-222me 2.2 5.5 38.7 4 4 2.1 coilcraft 74438356022 2.2 4.7 35 4.1 4.1 2.1 wurth elektronik 2mhz xfl4020-102me 1 5.4 11.9 4 4 2.1 coilcraft ihlp1212bzer1r0m-11 1 4.5 24 3 3.65 2.0 vishay spm4020t-1r0m-lr 1 5.6 28.1 4.1 4.4 2 tdk 3mhz 744383360068 0.68 4.5 27 3 3 2 wurth elektronik ihlp1212aeerr68m-11 0.68 5.4 22 3 3.65 1.5 vishay table 4. recommended inductors for 3a buck regulators f osc part number l (h) max i dc (a) max dcr (m) size in mm (l w h) manufacturer 1mhz xel4020-152me 1.5 7.4 23.6 4 4 2.1 coilcraft ihlp2020czer1r5m11 1.5 7 18.5 5.18 5.49 3 vishay 2mhz xel4020-821me 0.82 10.2 13 4 4 2 coilcraft fdv0530-h-r75m 0.75 9.7 7.6 6.2 5.8 3 toko 744383560068 0.68 8.2 9 4.1 4.1 2.1 wurth elektronik 3mhz fdsd0420d-r47m 0.47 6.8 18 4.2 4.2 2 toko ihlp1212aeerr47m-11 0.47 6.7 15 3 3.65 1.5 vishay table 5. recommended inductors for 4a buck regulators f osc part number l (h) max i dc (a) max dcr (m) size in mm (l w h) manufacturer 1mhz xel4020-102me 1 9 14.6 4 4 2.1 coilcraft 744316100 1 11.5 5.225 5.3 5.5 4.0 wurth elektronik 2mhz xel4020-561me 0.56 11.3 8.8 4 4 2.1 coilcraft fdv0530-h-r56m 0.56 11.1 6.3 6.2 5.8 3 toko spm4020t-r47m-lr 0.47 8.7 11.8 4.1 4.4 2 tdk 3mhz xel4014-331me 0.33 9 12 4 4 1.4 coilcraft 744383560033 0.33 9.6 7.2 4.1 4.1 2.1 wurth elektronik lt c3374a 3374af
18 for more information www.linear.com/LTC3374A a pplica t ions i n f or m a t ion pcb considerations when laying out the printed circuit board, the following list should be followed to ensure proper operation of the LTC3374A: 1. the exposed pad of the package (pin 39) should connect directly to a large ground plane to minimize thermal and electrical impedance. see the linear technology application note, application notes for thermally en - hanced leaded plastic packages, for the proper size and layout of the thermal vias and solder stencils. 2. all the input supply pins should each have a local de - coupling capacitor. 3. the connections to the switching regulator input supply pins and their respective decoupling capacitors should be kept as short as possible. the gnd side of these capacitors should connect directly to the ground plane of the part. these capacitors provide the ac current to the internal power mosfets and their drivers. it is important to minimize inductance from these capacitors to the v in pins of the LTC3374A. 4. the switching power traces connecting sw1, sw2, sw3, sw4, sw5, sw6, sw7, and sw8 to their respective inductors should be minimized to reduce radiated emi and parasitic coupling. due to the large voltage swing of the switching nodes, high input impedance sensitive nodes, such as the feedback nodes, should be kept far away or shielded from the switching nodes or poor performance could result. 5. the gnd side of the switching regulator output capaci - tors should connect directly to the thermal ground plane of the part. minimize the trace length from the output capacitor to the inductor(s)/pin(s). 6. in a combined buck regulator application the trace length of switch nodes to the inductor should be kept equal to ensure proper operation. lt c3374a 3374af
19 for more information www.linear.com/LTC3374A figure 3. detailed front page application (all 1a outputs) LTC3374A exposed pad 2.2h v in1 sw1 fb1 v in8 sw8 fb8 3374a f03 2.2h 536k 357k 232k 464k 10f 2.25v to 5.5v 2.0v 1a 1.2v 1a 22f 22f 10f 2.25v to 5.5v 2.2h v in2 sw2 fb2 v in7 sw7 fb7 2.2h 590k 475k 511k 162k 10f 3.3v to 5.5v 1.8v 1a 3.3v 1a 22f 22f 10f 2.25v to 5.5v 2.2h v in3 sw3 fb3 v in6 sw6 fb6 2.2h 715k 806k 549k 200k 10f 3.0v to 5.5v 1.5v 1a 3.0v 1a 22f 22f 10f 2.25v to 5.5v 2.2h v in4 sw4 fb4 402k rt en1 en2 en3 en4 en5 en6 en7 en8 sync mode v in5 sw5 fb5 v cc pgood_all temp microprocessor control 2.2h 255k 1.02m 665k 309k 10f 2.5v to 5.5v 1.0v 1a 2.5v 1a 22f 22f 2.7v to 5.5v microprocessor control 10f 2.25v to 5.5v 10f 1m a pplica t ions i n f or m a t ion lt c3374a 3374af
20 for more information www.linear.com/LTC3374A a pplica t ions i n f or m a t ion figure 4. buck regulators with sequenced start-up driven from a high voltage upstream buck converter (all 1a outputs) LTC3374A exposed pad 2.2h v in1 sw1 fb1 v in8 sw8 fb8 3374a f04 2.2h 536k 357k 232k 1m 464k 10f 1.2v 1a 3.3v 1a 3.0v 1a 2.5v 1a 2.0v 1a 10f 10f 10f 10f 10f 10f 10f 22f 22f 22f 22f 1.8v 1a 1.5v 1a 1.0v 1a 22f 22f 22f 22f 2.2h v in2 sw2 fb2 v in7 sw7 fb7 2.2h 590k 475k 511k 162k 2.2h v in3 sw3 fb3 v in6 sw6 fb6 2.2h 715k 806k 549k 200k 2.2h v in4 sw4 fb4 402k rt en1 en2 en3 en4 en5 en6 en7 en8 v in5 sw5 fb5 v cc pgood_all temp 2.2h 255k 1.02m 665k 309k microprocessor control 10f sync mode 0.1f c in 22f v in 5.5v to 36v intv cc 34.8k 470pf 100k 100k mtop, mbot: si7850dp l1 coilcraft ser1360-802kl c out : sanyo 10tpe330m d1: dfls1100 19.1k 2.2f d1 0.1f freq ith sgnd sgnd ltc3891 v in pgood pllin/mode i lim intv cc pgnd l1 8h r sense 7m boost sw bg sense + sense ? extv cc v fb tg mtop mbot 1nf c out 330f 5v 6a track/ss run v in en kill int pb tmr gnd on ltc2955ts8-1 microprocessor control microprocessor control 1m lt c3374a 3374af
21 for more information www.linear.com/LTC3374A a pplica t ions i n f or m a t ion figure 5. combined buck regulators with common input supply (4a, 3a, 1a) LTC3374A exposed pad 0.82h v in1 sw1 sw2 sw3 sw4 fb1 v in6 sw8 sw7 sw6 fb6 3374a f05 0.6h 655k 309k 232k 464k 2.5v 3a 1.2v 4a 2.7v to 5.5v 100f 68f 10f 10f 10f 10f 10f 10f 10f 10f v in2 fb2 v in7 fb7 v in3 fb3 v in8 fb8 2.2h v in4 fb4 rt en2 en3 en4 en7 en8 en1 en5 en6 sync mode v in5 sw5 fb5 pgood_all temp v cc microprocessor control 590k 475k 1.8v 1a 22f 10f microprocessor control 1m lt c3374a 3374af
22 for more information www.linear.com/LTC3374A p ackage descrip t ion 5.00 0.10 note: 1. drawing conforms to jedec package outline m0-220 variation whkd 2. drawing not to scale 3. all dimensions are in millimeters pin 1 top mark (see note 6) 37 1 2 38 bottom view?exposed pad 5.50 ref 5.15 0.10 7.00 0.10 0.75 0.05 r = 0.125 typ r = 0.10 typ 0.25 0.05 (uh) qfn ref c 1107 0.50 bsc 0.200 ref 0.00 ? 0.05 recommended solder pad layout apply solder mask to areas that are not soldered 3.00 ref 3.15 0.10 0.40 0.10 0.70 0.05 0.50 bsc 5.5 ref 3.00 ref 3.15 0.05 4.10 0.05 5.50 0.05 5.15 0.05 6.10 0.05 7.50 0.05 0.25 0.05 package outline 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.20mm on any side 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 notch r = 0.30 typ or 0.35 45 chamfer uhf package 38-lead plastic qfn (5mm 7mm) (reference ltc dwg # 05-08-1701 rev c) please refer to http://www.linear.com/products/LTC3374A#packaging for the most recent package drawings. lt c3374a 3374af
23 for more information www.linear.com/LTC3374A p ackage descrip t ion 4.75 (.187) ref fe38 (aa) tssop rev c 0910 0.09 ? 0.20 (.0035 ? .0079) 0 ? 8 0.25 ref 0.50 ? 0.75 (.020 ? .030) 4.30 ? 4.50* (.169 ? .177) 1 19 20 ref 9.60 ? 9.80* (.378 ? .386) 38 1.20 (.047) max 0.05 ? 0.15 (.002 ? .006) 0.50 (.0196) bsc 0.17 ? 0.27 (.0067 ? .0106) typ recommended solder pad layout 0.315 0.05 0.50 bsc 4.50 ref 6.60 0.10 1.05 0.10 4.75 ref 2.74 ref 2.74 (.108) millimeters (inches) *dimensions do not include mold flash. mold flash shall not exceed 0.150mm (.006") per side note: 1. controlling dimension: millimeters 2. dimensions are in 3. drawing not to scale see note 4 4. recommended minimum pcb metal size for exposed pad attachment 6.40 (.252) bsc fe package 38-lead plastic tssop (4.4mm) (reference ltc dwg # 05-08-1772 rev c) exposed pad variation aa please refer to http://www.linear.com/products/LTC3374A#packaging for the most recent package drawings. lt c3374a 3374af
24 for more information www.linear.com/LTC3374A ? linear technology corporation 2016 lt 0716 ? printed in usa r ela t e d p ar t s typical a pplica t ion part number description comments ltc3370/ ltc3371 4-channel 8a configurable 1a buck dc/dcs four synchronous buck regulators with 8 1a power stages. can connect up to four power stages in parallel to make a high current output (4a maximum) with a single inductor, 8 output configurations possible, precision pgood indication. ltc3371 has a watchdog timer. ltc3370: 32-lead 5mm 5mm qfn. ltc3371: 38-lead 5mm 7mm qfn and tssop lt c3374/ ltc3375 8-channel parallelable 1a buck dc/dcs eight 1a synchronous buck regulators. can connect up to four power stages in parallel to make a high current output (4a maximum) with a single inductor , 15 output configurations possible. ltc3375 has i 2 c programming with a watchdog timer and pushbutton. ltc3374: 38-lead 5mm 7mm qfn and tssop. ltc3375 48-lead 7mm 7mm qfn lt c3589 8-output regulator with sequencing and i 2 c triple i 2 c adjustable high efficiency step-down dc/dc converters: 1.6a, 1a, 1a. high efficiency 1.2a buck-boost dc/dc converter, triple 250ma ldo regulators. pushbutton on/off control with system reset, dynamic voltage scaling and slew rate control. selectable 2.25mhz/1.12mhz switching frequency, 8a standby current, 40-lead 6mm 6mm qfn. ltc3675 7-channel configurable high power pmic four synchronous buck dc/dcs (1a/1a/500ma/500ma). buck dc/dcs can be paralleled to deliver up to 2a with a single inductor. independent 1a boost and 1a buck-boost dc/dcs, always-on 25ma ldo. dual string i 2 c controlled 40v led driver. i 2 c programmable output voltage and read back of dc/dc, operating mode, and switch node slew rate for all dc/dcs. fault status, pushbutton on/off/reset, low quiescent current: 16a (all dc/dcs off), 4mm 7mm 44-lead qfn. linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com/LTC3374A LTC3374A exposed pad v in1 10f v in8 fb8 v in6 fb6 v in5 v in4 v in7 v in2 fb2 10f 10f 10f 0.68h 0.47h 10f 10f 47f sw7 sw8 sw5 sw6 fb5 rt fb7 v in3 fb3 fb1 sw1 sw2 sw3 10f 10f 68f 47f 511k 162k 0.68h 665k 309k 267k 3374a ta02 232k 464k 1.5h fb4 v cc pgood_all temp sync mode en1 en4 en5 en7 en2 en3 en6 en8 sw4 22f 10f microprocessor control 2.7v to 5.5v 2.25v to 5.5v 2.25v to 5.5v 3.3v to 5.5v 2.5v to 5.5v 3.3v 2a 2.5v 2a 1.8v 1a 1.2v 3a 590k 475k 1m combined bucks with 3mhz switching frequency and sequenced power up (3a, 1a, 2a, 2a) lt c3374a 3374af

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