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1 for more information www.linear.com/lt8610a typical application features description 42v, 3.5a synchronous step-down regulator with 2.5a quiescent current the lt ? 8610a/lt8610ab series are compact, high ef- ficiency, high speed synchronous monolithic step-down switching regulators that consume only 2.5 a of quies- cent current . compared to the lt8610, they have higher maximum output currents of 3.5 a and a faster minimum switch-on time of 30 ns. the lt8610a has the same low ripple burst mode performance of the lt8610, while the lt8610ab has even higher light load efficiency. the other features of the lt8610 remain unchanged in the lt8610a/lt8610ab series. a sync pin allows synchroni - zation to an external clock. the en/uv pin has an accurate 1v threshold for v in undervoltage lockout or shut down. a capacitor on the tr/ss pin programs the output voltage ramp rate during startup. the pg flag signals when v out is within 9% of the programmed output voltage as well as fault conditions. output current minimum on time 1 ma load efficiency** lt8610* 2.5a 50ns 82% lt8610a 3.5a 30ns 82% lt8610ab 3.5a 30ns 91% *see lt8610 data sheet. **v in = 12v, v out = 3.3v, l = 4.7h 5v 3.5a step-down converter applications n lt8610 feature set, plus: 3.5a maximum output current fast 30ns minimum switch-on time improved burst mode efficiency ( lt8610ab only ) improved emi n wide input voltage range: 3.4v to 42v n ultralow quiescent current burst mode ? operation: 2.5a i q regulating 12v in to 3.3v out n fixed output voltages: 3.3v, 5v n output ripple < 10mv p-p (lt8610a only) n high efficiency synchronous operation: 95% efficiency at 1a, 5v out from 12v in 93% efficiency at 1a, 3.3v out from 12v in n low dropout under all conditions: 200mv at 1a n safely tolerates inductor saturation in overload n adjustable and synchronizable frequency: 200khz to 2.2mhz n accurate 1v enable pin threshold n output soft-start and tracking n small thermally enhanced 16-lead msop package n automotive and industrial supplies n gsm power supplies l, lt , lt c , lt m , burst mode, linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. bst v in en/uv pg sync intv cc tr/ss rt sw lt8610ab-5 gnd bias 8610ab ta01a v out 0.1f v out 5v 3.5a 4.7f v in 5.5v to 42v 1f 10nf 4.7h f sw = 700khz 60.4k 47f 2 lt8610ab efficiency at 5v out 0.1 1 1000 100 10 load current (ma) efficiency (%) 80 90 100 8610ab ta01b 70 50 60 40 30 v in = 12v v in = 24v v in = 36v lt8610a/lt8610ab series 8610abfa
2 for more information www.linear.com/lt8610a absolute maximum ratings v in , en / uv , pg .......................................................... 42 v b ias .......................................................................... 30 v bs t pin above sw pin ................................................4v fb , tr / ss , rt, intv cc . .............................................. 4v v out , sync voltage . .................................................. 6v op erating junction temperature range ( note 2) lt 86 10 ae / lt 8610 abe ........................... C 40 to 125 c lt 86 10 ai / lt 8610 abi ............................. C 40 to 125 c lt 86 10 ah / lt 8610 abh .......................... C 40 to 150 c storage temperature range ...................... C 65 to 150 c (note 1) order information lead free finish tape and reel part marking* package description temperature range lt8610aemse#pbf lt8610aemse#trpbf 8610a 16-lead plastic msop C40c to 125c lt8610aemse-3.3#pbf lt8610aemse-3.3#trpbf 610a33 16-lead plastic msop C40c to 125c lt8610aemse-5#pbf lt8610aemse-5#trpbf 8610a5 16-lead plastic msop C40c to 125c lt8610aimse#pbf lt8610aimse#trpbf 8610a 16-lead plastic msop C40c to 125c lt8610aimse-3.3#pbf lt8610aimse-3.3#trpbf 610a33 16-lead plastic msop C40c to 125c lt8610aimse-5#pbf lt8610aimse-5#trpbf 8610a5 16-lead plastic msop C40c to 125c lt8610ahmse#pbf lt8610ahmse#trpbf 8610a 16-lead plastic msop C40c to 150c lt8610ahmse-3.3#pbf lt8610ahmse-3.3#trpbf 610a33 16-lead plastic msop C40c to 150c lt8610ahmse-5#pbf lt8610ahmse-5#trpbf 8610a5 16-lead plastic msop C40c to 150c lt8610abemse#pbf lt8610abemse#trpbf 8610ab 16-lead plastic msop C40c to 125c lt8610abemse-3.3#pbf lt8610abemse-3.3#trpbf 10ab33 16-lead plastic msop C40c to 125c lt8610abemse-5#pbf lt8610abemse-5#trpbf 610ab5 16-lead plastic msop C40c to 125c lt8610abimse#pbf lt8610abimse#trpbf 8610ab 16-lead plastic msop C40c to 125c lt8610abimse-3.3#pbf lt8610abimse-3.3#trpbf 10ab33 16-lead plastic msop C40c to 125c lt8610abimse-5#pbf lt8610abimse-5#trpbf 610ab5 16-lead plastic msop C40c to 125c lt8610abhmse#pbf lt8610abhmse#trpbf 8610ab 16-lead plastic msop C40c to 150c lt8610abhmse-3.3#pbf lt8610abhmse-3.3#trpbf 10ab33 16-lead plastic msop C40c to 150c lt8610abhmse-5#pbf lt8610abhmse-5#trpbf 610ab5 16-lead plastic msop C40c to 150c consult lt c marketing for parts specified with wider operating temperature ranges. *the temperature grade is identified by a label on the shipping container. consult lt c marketing for information on non-standard lead based finish parts. 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/ lt8610a, lt8610ab lt8610a-3.3, lt8610a-5, lt8610ab-3.3, lt8610ab-5 1 2 3 4 5 6 7 8 sync tr/ss rt en/uv v in v in nc gnd 16 15 14 13 12 11 10 9 fb pg bias intv cc bst sw sw sw top view 17 gnd mse package 16-lead plastic msop ja = 40c/w, jc( pad ) = 10c/w exposed pad ( pin 17) is gnd, must be soldered to pcb 1 2 3 4 5 6 7 8 sync tr/ss rt en/uv v in v in nc gnd 16 15 14 13 12 11 10 9 v out pg bias intv cc bst sw sw sw top view 17 gnd mse package 16-lead plastic msop ja = 40c/w, jc( pad ) = 10c/w exposed pad ( pin 17) is gnd, must be soldered to pcb pin configuration lt8610a/lt8610ab series 8610abfa
3 for more information www.linear.com/lt8610a electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. parameter conditions min typ max units minimum input voltage (note 4) l 2.9 3.4 v v in quiescent current v en/uv = 0v l 1.0 1.0 3 8 a a v en/uv = 2v, not switching, v sync = 0v l 1.7 1.7 4 10 a a v en/uv = 2v, not switching, v sync = 2v 0.26 0.5 ma v in current in regulation v out = 0.97v, v in = 6v, output load = 100a (lt8610a) v out = 0.97v, v in = 6v, output load = 1ma (lt8610a) v out = 0.97v, v in = 6v, output load = 100a (lt8610ab) v out = 0.97v, v in = 6v, output load = 1ma (lt8610ab) l l l l 24 210 24 210 50 350 50 350 a a a a v in current in regulation v out = 3.3v, v in = 8v, output load = 100a (lt8610a-3.3) v out = 3.3v, v in = 8v, output load = 1ma (lt8610a-3.3) v out = 3.3v, v in = 8v, output load = 100a (lt8610ab-3.3) v out = 3.3v, v in = 8v, output load = 1ma (lt8610ab-3.3) v out = 5v, v in = 8v, output load = 100a (lt8610a-5) v out = 5v, v in = 8v, output load = 1ma (lt8610a-5) v out = 5v, v in = 8v, output load = 100a (lt8610ab-5) v out = 5v, v in = 8v, output load = 1ma (lt8610ab-5) l l l l l l l l 60 540 55 500 100 790 80 730 120 900 100 800 180 1200 150 1100 a a a a a a a a feedback reference v oltage (lt8610a/lt8610ab) v in = 6v, i load = 0.5a v in = 6v, i load = 0.5a l 0.964 0.958 0.970 0.970 0.976 0.982 v v output v oltage (lt8610a-3.3/lt8610ab-3.3) v in = 8v, i load = 0.5a v in = 8v, i load = 0.5a l 3.28 3.26 3.30 3.30 3.32 3.34 v v output v oltage (lt8610a-5/lt8610ab-5) v in = 8v, i load = 0.5a v in = 8v, i load = 0.5a l 4.97 4.94 5.00 5.00 5.03 5.06 v v feedback v oltage line regulation (lt8610a/lt8610ab) v in = 4v to 42v, i load = 1a l 0.004 0.02 %/v voltage line regulation (lt8610a-3.3/lt8610ab-3.3) v in = 4v to 42v, i load = 1a l 0.004 0.02 %/v voltage line regulation (lt8610a-5/lt8610ab-5) v in = 6v to 42v, i load = 1a l 0.004 0.02 %/v feedback pin input current (lt8610a/lt8610ab) v fb = 1v C20 20 na internal feedback resistor divider (lt8610a-3.3/lt8610ab-3.3) 14.3 m internal feedback resistor divider (lt8610a-5/lt8610ab-5) 12.5 m int v cc voltage i load = 0ma, v bias = 0v i load = 0ma, v bias = 3.3v 3.23 3.25 3.4 3.29 3.57 3.35 v v intv cc undervoltage lockout 2.5 2.6 2.7 v bias pin current consumption v bias = 3.3v, i load = 1a, 2mhz 9 ma minimum on-time i load = 1a, sync = 0v i load = 1a, sync = 3.3v l l 15 15 30 30 45 45 ns ns minimum off-t ime 95 125 ns lt8610a/lt8610ab series 8610abfa
4 for more information www.linear.com/lt8610a the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. electrical characteristics parameter conditions min typ max units oscillator frequency r t = 221k, i load = 1a r t = 60.4k, i load = 1a r t = 18.2k, i load = 1a l l l 180 665 1.85 210 700 2.00 240 735 2.15 khz khz mhz to p power nmos on-resistance i sw = 1a 120 m top power nmos current limit lt8610a lt8610ab l l 5 5 6.7 6.7 8 8 a a bottom power nmos on-resistance v intvcc = 3.4v, i sw = 1a 65 m bottom power nmos current limit v intvcc = 3.4v 3.4 4.3 5.4 a sw leakage current v in = 42v, v sw = 0v, 42v C1.5 1.5 a en/uv pin threshold en/uv rising l 0.94 1.0 1.06 v en/uv pin hysteresis 40 mv en/uv pin current v en/uv = 2v C20 20 na pg upper threshold offset from v fb v fb falling l 6 9.0 12 % pg lower threshold offset from v fb v fb rising l C12 C9.0 C6 % pg hysteresis 1.3 % pg leakage v pg = 3.3v C40 40 na pg pull-down resistance v pg = 0.1v l 680 2000 sync threshold sync falling sync rising 0.8 1.6 1.1 2.0 1.4 2.4 v v sync pin current v sync = 6v C40 40 na tr/ss source current l 1.0 2.0 3.2 a tr/ss pull-down resistance fault condition, tr/ss = 0.1v 230 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 lt8610ae/lt8610abe is guaranteed to meet performance specifications from 0c to 125c junction temperature. specifications over the C40c to 125c operating junction temperature range are assured by design, characterization, and correlation with statistical process controls. the lt8610ai/lt8610abi is guaranteed over the full C40c to 125c operating junction temperature range. the lt8610ah is guaranteed over the full C40c to 150c operating junction temperature range. high junction temperatures degrade operating lifetimes. operating lifetime is derated at junction temperatures greater than 125c. note 3: this ic includes overtemperature protection that is intended to protect the device during overload conditions. junction temperature will exceed 150c when overtemperature protection is active. continuous operation above the specified maximum operating junction temperature will reduce lifetime. note 4: for fixed output voltage versions, minimum input voltage will be limited by output voltage. lt8610a/lt8610ab series 8610abfa
5 for more information www.linear.com/lt8610a typical performance characteristics lt8610ab efficiency at 3.3v out lt8610a efficiency at 5v out lt8610a efficiency at 5v out lt8610a efficiency at 3.3v out lt8610a efficiency at 3.3v out lt8610a/lt8610ab efficiency vs frequency at 1a lt8610ab efficiency at 5v out lt8610ab efficiency at 5v out lt8610ab efficiency at 3.3v out load current (a) 0 efficiency (%) 80 90 100 2 3 8610ab g01 70 60 75 85 95 65 55 50 0.5 1 1.5 3.5 2.5 f sw = 700khz l = ihlp-2020bz-01, 4.7h v in = 12v v in = 24v v in = 36v load current (ma) efficiency (%) 0.01 101 1000 100 8610ab g03 0.1 80 90 100 70 50 60 40 20 30 v in = 12v v in = 24v v in = 36v f sw = 700khz l = ihlp-2020bz-01, 4.7h 0 2 3 0.5 1 1.5 3.5 2.5 load current (a) efficiency (%) 80 90 100 8610ab g02 70 60 75 85 95 65 55 50 v in = 12v v in = 24v v in = 36v f sw = 700khz l = ihlp-2020bz-01, 4.7h 0.01 101 1000 100 0.1 v in = 12v v in = 24v v in = 36v load current (ma) 30 efficiency (%) 90 100 80 50 70 60 40 8610ab g04 20 f sw = 700khz l = ihlp-2020bz-01, 4.7h load current (a) 0 efficiency (%) 80 90 100 2 3 8610ab g42 70 60 75 85 95 65 55 50 0.5 1 1.5 3.5 2.5 f sw = 700khz l = ihlp-2020bz-01, 4.7h v in = 12v v in = 24v v in = 36v load current (ma) efficiency (%) 0.01 101 1000 100 8610ab g43 0.1 80 90 100 70 50 60 40 20 30 v in = 12v v in = 24v v in = 36v f sw = 700khz l = ihlp-2020bz-01, 4.7h 0 2 3 0.5 1 1.5 3.5 2.5 load current (a) efficiency (%) 80 90 100 8610ab g44 70 60 75 85 95 65 55 50 v in = 12v v in = 24v v in = 36v f sw = 700khz l = ihlp-2020bz-01, 4.7h 0.01 101 1000 100 0.1 v in = 12v v in = 24v v in = 36v load current (ma) 30 efficiency (%) 90 100 80 50 70 60 40 8610ab g45 20 f sw = 700khz l = ihlp-2020bz-01, 4.7h switching frequency (mhz) 0.25 80 85 100 1.75 8610ab g05 75 70 0.75 1.25 2.25 1.50 0.50 1.00 2.00 65 60 90 95 efficiency (%) v in = 12v v in = 24v v out = 3.3v l = ihlp-2020bz-01, 4.7h lt8610a/lt8610ab series 8610abfa
6 for more information www.linear.com/lt8610a typical performance characteristics line regulation lt8610a no load supply current lt8610ab no load supply current no load supply current reference voltage lt8610a-3.3 output voltage lt8610ab-3.3 output voltage en pin thresholds load regulation temperature (c) ?55 0.955 reference voltage (v) 0.958 0.964 0.967 0.970 0.985 0.976 5 65 95 125 8610ab g06 0.961 0.979 0.982 0.973 ?25 35 155 temperature (c) ?55 3.240 output voltage (v) 3.255 3.285 3.300 3.315 3.360 3.345 5 65 95 125 8610ab g46 3.270 3.330 ?25 35 155 temperature (c) ?55 4.900 output voltage (v) 4.925 4.975 5.000 5.025 5.100 5.075 5 65 95 125 8610ab g47 4.950 5.050 ?25 35 155 temperature (c) ?55 en threshold (v) 65 8610ab g07 5 ?25 95 125 35 155 0.95 0.96 0.98 0.99 1.00 1.02 0.97 1.01 en rising en falling load current (a) 0 ?0.25 change in v out (%) ?0.15 ?0.05 0.05 0.5 1 1.5 2 8610ab g08 2.5 0.15 0.25 ?0.20 ?0.10 0 0.10 0.20 3.5 3 v out = 3.3v v in = 12v input voltage (v) 0 change in v out (%) 0.03 0.09 0.15 40 8610ab g09 ?0.03 ?0.09 0 0.06 0.12 ?0.06 ?0.12 ?0.15 105 2015 30 35 45 25 v out = 3.3v i load = 0.5a input voltage (v) 0 0 input current (a) 0.5 1.5 2.0 2.5 5.0 3.5 10 20 25 40 8610ab g10 1.0 4.0 4.5 3.0 5 15 30 35 tested in regulation 8610a: v out = 3.3v 8610a-3.3 8610a-5 8610a input voltage (v) 0 0 input current (a) 0.5 1.5 2.0 2.5 5.0 3.5 10 20 25 40 8610ab g48 1.0 4.0 4.5 3.0 5 15 30 35 tested in regulation 8610ab: v out = 3.3v 8610ab-3.3 8610ab-5 8610ab temperature (c) ?55 ?25 0 input current (a) 10 25 5 65 95 8610ab g11 5 20 15 35 125 155 v out = 3.3v v in = 12v in regulation lt8610a/lt8610ab series 8610abfa
7 for more information www.linear.com/lt8610a top fet current limit vs duty cycle top fet current limit bottom fet current limit duty cycle 0 current limit (a) 3.5 4.0 4.5 0.6 1.0 8610ab g13 3.0 0.2 0.4 0.8 5.0 5.5 8.0 7.0 7.5 6.5 6.0 temperature (c) ?55 4.50 current limit (a) 4.75 5.00 5.25 5.50 5.75 6.00 6.25 6.50 6.75 7.00 ?25 5 35 65 8610ab g14 95 125 30% dc temperature (c) ?55 3.00 current limit (a) 3.25 3.50 3.75 4.00 5.50 ?25 5 35 65 8610ab g15 95 155 125 4.25 4.50 4.75 5.00 5.25 typical performance characteristics minimum on-time minimum off-time dropout voltage switching frequency switch drop switch drop temperature (c) ?55 ?25 0 switch drop (mv) 100 250 5 65 95 8610ab g40 50 200 150 35 125 155 top sw bot sw switch current = 1a switch current (a) 0 0 switch drop (mv) 50 150 200 250 2 450 8610ab g41 100 1 0.5 2.5 1.5 3 300 350 400 top sw bot sw temperature (c) ?55 25 27 29 31 minimum on-time (ns) 33 35 37 39 45 5 65 95 125 8610ab g17 43 41 ?25 35 155 v out = 3.3v v out = 0.97v i load = 1.5a v sync = 0v temperature (c) ?50 minimum off-time (ns) 95 35 8610ab g18 80 ?25 5 65 75 125 120 115 110 105 100 90 85 95 125 155 v out = 3.3v i load = 0.5a load current (a) dropout voltage (v) 400 8610ab g19 200 0 600 800 300 100 500 700 0 0.5 1 1.5 2 2.5 3.5 3 temperature (c) ?55 switching frequency (khz) 730 35 8610ab g20 700 680 ?25 5 65 670 660 740 r t = 60.4k 720 710 690 95 125 155 lt8610a/lt8610ab series 8610abfa
8 for more information www.linear.com/lt8610a typical performance characteristics soft-start tracking soft-start current pg high thresholds rt programmed switching frequency pg low thresholds v in uvlo tr/ss voltage (v) 0 fb voltage (v) 0.8 1.0 1.2 0.6 1.0 8610ab g23 0.6 0.4 0.2 0.4 0.8 1.2 1.4 0.2 0 temperature (c) ?50 ss pin current (a) 2.3 35 8610ab g24 2.0 1.8 ?25 5 65 1.7 1.6 2.4 2.2 2.1 1.9 95 125 155 v ss = 0.5v temperature (c) ?55 7.0 pg threshold offset from v ref (%) 7.5 8.5 9.0 9.5 12.0 10.5 5 65 95 125 8610ab g25 8.0 11.0 11.5 10.0 ?25 35 155 fb rising fb falling switching frequency (mhz) 0.2 rt pin resistor (k) 150 200 250 1.8 8610ab g27 100 50 125 175 225 75 25 0 0.6 1 1.4 2.2 temperature (c) ?55 input voltage (v) 3.4 35 8610ab g28 2.8 2.4 ?25 5 65 2.2 2.0 3.6 3.2 3.0 2.6 95 125 155 temperature (c) ?55 ?12.0 pg threshold offset from v ref (%) ?11.5 ?10.5 ?10.0 ?9.5 ?7.0 ?8.5 5 65 95 125 8610ab g26 ?11.0 ?8.0 ?7.5 ?9.0 ?25 35 155 fb rising fb falling minimum load to full frequency burst frequency frequency foldback input voltage (v) load current (ma) 60 70 80 15 25 40 8610ab g39 40 20 0 50 30 10 5 10 20 30 35 v out = 3.3v f sw = 700khz pulse-skipping mode fb voltage (v) 0 switching frequency (khz) 300 400 500 0.6 1 8610ab g22 200 100 0 0.2 0.4 0.8 600 700 800 v out = 3.3v v in = 12v v sync = 0v r t = 60.4k load current (ma) 0 switching frequency (khz) 400 500 600 800 8610ab g21 300 200 0 200 400 600 700 100 300 500 100 800 v in = 12v v out = 3.3v l = 4.7h lt8610a lt8610ab 700 lt8610a/lt8610ab series 8610abfa
9 for more information www.linear.com/lt8610a bias pin current bias pin current input voltage (v) 5 bias pin current (ma) 4.5 5.5 45 8610ab g29 3.5 2.5 15 25 35 10 20 30 40 6.5 4.0 5.0 3.0 6.0 v bias = 5v v out = 5v i load = 1a f sw = 700khz switching frequency (mhz) 0 0 bias pin current (ma) 2 4 6 8 10 12 0.5 1 1.5 2 8610ab g30 2.5 v bias = 5v v out = 5v v in = 12v i load = 1a typical performance characteristics switching waveforms switching waveforms switching waveforms lt8610a/lt8610ab transient response lt8610a/lt8610ab transient response start-up dropout performance start-up dropout performance i l 1a/div v sw 5v/div 500ns/div 12v in to 5v out at 1a 8610ab g31 i l 200ma/div v sw 5v/div 500s/div 12v in to 5v out at 10ma v sync = 0v (lt8610a) 8610ab g32 i l 1a/div v sw 10v/div 500ns/div 36v in to 5v out at 1a 8610ab g33 i l 2a/div v out 200mv/div 50s/div 1.5a to 3.5a transient 12v in , 3.3v out c out = 47f 8610ab g34 i l 2a/div v out 200mv/div 50s/div 30ma to 2a transient 12v in , 3.3v out c out = 47f 8610ab g35 v in 2v/div v out 2v/div 100ms/div 2.5 load (2a in regulation) 8610ab g37 v in v out v in 2v/div v out 2v/div 100ms/div 20 load (250ma in regulation) 8610ab g38 v in v out lt8610a/lt8610ab series 8610abfa
10 for more information www.linear.com/lt8610a pin functions sync (pin 1): external clock synchronization input. ground this pin for low ripple burst mode operation at low output loads. tie to a clock source for synchronization to an external frequency. apply a dc voltage of 3 v or higher or tie to intv cc for pulse-skipping mode. when in pulse- skipping mode, the i q will increase to several hundred a. do not float this pin. tr/ss (pin 2): output tracking and soft-start pin. this pin allows user control of output voltage ramp rate dur - ing start -up. a tr/ss voltage below 0.97 v forces the lt8610a/lt8610ab to regulate the fb pin to equal the tr/ss pin voltage. when tr/ss is above 0.97 v, the tracking function is disabled and the internal reference resumes control of the error amplifier. an internal 2.2a pull-up current from intv cc on this pin allows a capacitor to program output voltage slew rate. this pin is pulled to ground with an internal 230 mosfet during shutdown and fault conditions; use a series resistor if driving from a low impedance output. this pin may be left floating if the tracking function is not needed. rt (pin 3): a resistor is tied between rt and ground to set the switching frequency. en/uv (pin 4): the lt8610a/lt8610ab is shut down when this pin is low and active when this pin is high. the hysteretic threshold voltage is 1.00 v going up and 0.96v going down. tie to v in if the shutdown feature is not used. an external resistor divider from v in can be used to program a v in threshold below which the lt8610a/ lt8610ab will shut down. v in ( pins 5, 6): the v in pins supply current to the lt8610 a/ lt8610ab internal circuitry and to the internal topside power switch. these pins must be tied together and be locally bypassed. be sure to place the positive terminal of the input capacitor as close as possible to the v in pins, and the negative capacitor terminal as close as possible to the gnd pins. nc (pin 7): no connect. this pin is not connected to internal circuitry. sw (pins 9, 10, 11): the sw pins are the outputs of the internal power switches. tie these pins together and con - nect them to the inductor and boost capacitor. this node should be kept small on the pcb for good per formance. bst ( pin 12): this pin is used to provide a drive voltage, higher than the input voltage, to the topside power switch. place a 0.1 f boost capacitor as close as possible to the ic. intv cc (pin 13): internal 3.4 v regulator bypass pin. the internal power drivers and control circuits are pow- ered from this voltage. intv cc maximum output cur- rent is 20 ma. do not load the intv cc pin with external circuitry. intv cc current will be supplied from bias if v bias > 3.1 v, otherwise current will be drawn from v in . voltage on intv cc will vary between 2.8 v and 3.4 v when v bias is between 3.0 v and 3.6v . decouple this pin to power ground with at least a 1 f low esr ceramic capacitor placed close to the ic. bias ( pin 14): the internal regulator will draw current from bias instead of v in when bias is tied to a voltage higher than 3.1 v. for output voltages of 3.3 v and above this pin should be tied to v out . if this pin is tied to a supply other than v out use a 1f local bypass capacitor on this pin. pg (pin 15): the pg pin is the open-drain output of an internal comparator. pg remains low until the fb pin is within 9% of the final regulation voltage, and there are no fault conditions. pg is valid when v in is above 3.4v, regardless of en/uv pin state. fb (pin 16, lt8610a/lt8610ab only): the lt8610a/ lt8610ab regulates the fb pin to 0.970 v. connect the feedback resistor divider tap to this pin. also, connect a phase lead capacitor between fb and v out . typically, this capacitor is 4.7pf to 10pf. v out (pin 16, lt8610a-3.3/lt8610a-5/lt8610ab-3.3/ lt8610ab-5 only): the lt8610a-3.3 and lt8610ab-3.3 regulate the v out pin to 3.3v . this pin connects to a 14.3 m internal feedback divider that programs the fixed output. the lt8610a-5 and lt8610ab-5 regulate the v out pin to 5 v. this pin connects to a 12.5 m internal feedback divider that programs the fixed output. gnd (pin 8, exposed pad pin 17): ground. these pins are the return path of the internal bottom-side switch and must be tied together. place the negative terminal of the input capacitor as close to the gnd pin and exposed pad as possible. the exposed pad must be soldered to the pcb in order to lower the thermal resistance. lt8610a/lt8610ab series 8610abfa
11 for more information www.linear.com/lt8610a block diagram + + ? + ? slope comp internal 0.97v ref oscillator 200khz to 2.2mhz burst detect 3.4v reg m1 m2 c bst c out v out 8610ab bd sw l bst 9-11 switch logic and anti- shoot through error amp shdn 9% v c shdn tsd intv cc uvlo v in uvlo lt8610a-3.3/lt8610a-5 lt8610ab-3.3/lt8610ab-5 only lt8610a/lt8610ab only shdn tsd v in uvlo en/uv 1v + ? 4 12 3 rt 1 sync 17 gnd intv cc 13 bias 14 gnd 8 pg 15 fb r1c1 r3 opt r4 opt r2 r2 r t c ss opt v out 16 tr/ss 2.2a 2 v in v in c in c vcc 5, 6 r1 c1 v out v out 16 lt8610a/lt8610ab series 8610abfa
12 for more information www.linear.com/lt8610a operation the lt8610 a/ lt8610ab is a monolithic, constant frequency, current mode step- down dc/ dc converter. an oscillator, with frequency set using a resistor on the rt pin, turns on the internal top power switch at the beginning of each clock cycle. current in the inductor then increases until the top switch current comparator trips and turns off the top power switch. the peak inductor current at which the top switch turns off is controlled by the voltage on the internal vc node. the error amplifier servos the vc node by comparing the voltage on the v fb pin with an internal 0.97 v reference. when the load current increases it causes a reduction in the feedback voltage relative to the reference leading the error amplifier to raise the vc voltage until the average inductor current matches the new load current. when the top power switch turns off, the synchronous power switch turns on until the next clock cycle begins or inductor current falls to zero. if overload conditions result in more than 3.3a flowing through the bottom switch, the next clock cycle will be delayed until switch current returns to a safe level. if the en/uv pin is low , the lt8610a/lt8610ab is shut down and draws 1 a from the input. when the en/uv pin is above 1v, the switching regulator will become active. to optimize efficiency at light loads, the lt8610 a/ lt8610ab operates in burst mode operation in light load situations. between bursts, all circuitry associated with controlling the output switch is shut down, reducing the input supply current to 1.7a . in a typical application, 2.5a will be consumed from the input supply when regulating with no load. the sync pin is tied low to use burst mode operation and can be tied to a logic high to use pulse- skipping mode. if a clock is applied to the sync pin the part will synchronize to an external clock frequency and operate in pulse-skipping mode. while in pulse-skipping mode the oscillator operates continuously and positive sw transitions are aligned to the clock. during light loads, switch pulses are skipped to regulate the output and the quiescent current will be several hundred a. to improve efficiency across all loads, supply current to internal circuitry can be sourced from the bias pin when biased at 3.3 v or above. else, the internal circuitry will draw current from v in . the bias pin should be connected to v out if the lt8610a/lt8610ab output is programmed at 3.3v or above. comparators monitoring the fb pin voltage ( or v out pin voltages for fixed output versions) will pull the pg pin low if the output voltage varies more than 9% ( typical) from the set point, or if a fault condition is present. the oscillator reduces the lt8610 a/ lt8610ab s operating frequency when the voltage at the fb pin ( or v out pin for fixed output versions) is low. this frequency foldback helps to control the inductor current when the output voltage is lower than the programmed value which occurs during start-up or overcurrent conditions. when a clock is ap - plied to the sync pin or the sync pin is held dc high, the frequency foldback is disabled and the switching frequency will slow down only during overcurrent conditions. the lt8610ab differs from the lt8610a in that it has improved efficiency during burst mode operation. this comes with the trade-off of increased output voltage ripple, which can be proportionally decreased with an increase in output capacitance. the other trade-off is that the lt8610ab will not reach the full switching frequency programmed by the rt pin resistor until a higher load compared to the lt8610a. lt8610a/lt8610ab series 8610abfa
13 for more information www.linear.com/lt8610a (2a) (2b) applications information resulting in much higher light load efficiency than for typi- cal converters . by maximizing the time between pulses, the converter quiescent current approaches 2.5 a for a typical application when there is no output load. therefore, to optimize the quiescent current performance at light loads, the current in the feedback resistor divider must be minimized as it appears to the output as load current. the fixed output versions of the lt8610 a/ lt8610ab series have larger internal feedback resistors than can practically be used externally, so are a good choice for optimizing quiescent current performance. while in burst mode operation the current limit of the top switch is approximately 400 ma for the lt8610a resulting in output voltage ripple shown in figure 2 a. the lt8610ab has a 1 a current limit in burst mode operation, which increases the efficiency but also the output voltage ripple compared to the the lt8610a (figure 2 b). however, increasing the output capacitance will decrease the output ripple proportionally ( table 1). as load ramps upward from zero the switching frequency will increase but only up to the switching frequency programmed by the resistor at the rt pin as shown in figure 1 a. the output load at figure 1. sw frequency vs load information in burst mode operation (1a) and pulse-skipping mode (1b) figure 2. burst mode operation of lt8610a (2a) and lt8610ab (2b) minimum load to full frequency burst frequency (1a) (1b) load current (ma) 0 switching frequency (khz) 400 500 600 800 8610ab f01a 300 200 0 200 400 600 700 100 300 500 100 800 v in = 12v v out = 3.3v l = 4.7h lt8610a lt8610ab 700 input voltage (v) load current (ma) 60 70 80 15 25 40 8610ab f01b 40 20 0 50 30 10 5 10 20 30 35 v out = 3.3v f sw = 700khz pulse-skipping mode i l 200ma/div v out 10mv/div 5s/div v sync = 0v c out = 47f l = 4.7h 8610ab f02a lt8610a i l 500ma/div v out 20mv/div v sw 5v/div 20s/div v sync = 0v c out = 47f l = 4.7h 8610ab f02b lt8610ab achieving ultralow quiescent current to enhance efficiency at light loads, the lt8610 a/ lt8610ab operates in low ripple burst mode operation, which keeps the output capacitor charged to the desired output voltage while minimizing the input quiescent current and minimiz - ing output voltage ripple. in burst mode operation the lt8610a/lt8610ab delivers single pulses of current to the output capacitor followed by sleep periods where the output power is supplied by the output capacitor. while in sleep mode the lt8610a/lt8610ab consumes 1.7a. as the output load decreases, the frequency of single cur - rent pulses decreases ( see figure 1 a) and the percentage o f time the lt8610 a/ lt8610ab is in sleep mode increases, lt8610a/lt8610ab series 8610abfa
14 for more information www.linear.com/lt8610a applications information which the lt8610a/lt8610ab reaches the programmed frequency varies based on input voltage, output voltage, and inductor choice. however, the output load required to reach full frequency will be higher for the lt8610ab as compared to the lt8610a (figure 1a). inductor value has a very strong effect on burst mode ef - ficiency. larger value inductors allow more charge to be transferred to the output per pulse, which increases both efficiency and output voltage ripple. this dependence on inductance is stronger for the lt8610ab than it is for the lt8610a. if higher efficiency is needed in a burst mode ap - plication, increasing inductor value can be a quick solution. table 1. output voltage ripple vs output capacitance for lt8610ab when v in = 12v, v out = 3.3v, and l = 4.7h output capacitance output ripple 47f 40mv 47f 2 20mv 47f 4 10mv for some applications it is desirable for the lt8610a/ lt8610ab to operate in pulse-skipping mode, offering two major differences from burst mode operation. first is the clock stays awake at all times and all switching cycles are aligned to the clock. in this mode much of the internal circuitry is awake at all times, increasing quiescent current to several hundred a. second is that full switching frequency is reached at lower output load than in burst mode operation ( see figure 1b). to enable pulse-skipping mode, the sync pin is tied high either to a logic output or to the intv cc pin. when a clock is applied to the sync pin the lt8610a/lt8610ab will also operate in pulse-skipping mode. fb resistor network the output voltage is programmed with a resistor divider between the output and the fb pin. choose the resistor values according to: r1 = r2 v out 0.970v C 1 ? ? ? ? ? ? (1) reference designators refer to the block diagram . 1% resistors are recommended to maintain output voltage accuracy. when using large fb resistors, a 4.7 pf to 10 pf phase-lead capacitor should be connected from v out to fb. the fixed output versions of the lt8610a/lt8610ab series have the feedback resistor network and phase lead capacitor integrated within the part. the fb pin is replaced with a v out pin for these regulators. the v out pin can be connected directly to the inductor and output capacitor. the 3.3 v fixed output products (lt8610a-3.3/ lt8610ab-3.3) have a total of 14.3 m of internal feedback divider resistance from the v out pin to ground. the 5v fixed output products ( lt8610a-5/lt8610ab-5) have a total of 12.5 m of internal feedback divider resistance from the v out pin to ground. if low input quiescent current and good light - load efficiency are desired, use large resistor values for the fb resistor divider. the current flowing in the divider acts as a load current, and will increase the no-load input current to the converter, which is approximately: i q = 1.7a + v out r1 + r2 ? ? ? ? ? ? v out v in ? ? ? ? ? ? 1 n ? ? ? ? ? ? (2) where 1.7 a is the quiescent current of the lt8610a/ lt8610ab and the second term is the current in the feed- back divider reflected to the input of the buck operating at its light load efficiency n. for a 3.3 v application with r1 = 1 m and r2 = 412 k, the feedback divider draws 2.3a. with v in = 12 v and n = 80%, this adds 0.8 a to the 1.7a quiescent current resulting in 2.5 a no-load current from the 12 v supply. note that this equation implies that the no-load current is a function of v in ; this is plotted in the typical performance characteristics section. setting the switching frequency the lt8610a/lt8610ab uses a constant frequency pwm architecture that can be programmed to switch from 200khz to 2.2 mhz by using a resistor tied from the rt pin to ground. a table showing the necessary r t value for a desired switching frequency is in table 1. the r t resistor required for a desired switching frequency can be calculated using: r t = 46.5 f sw C 5.2 (3) lt8610a/lt8610ab series 8610abfa
15 for more information www.linear.com/lt8610a applications information where r t is in k and f sw is the desired switching fre- quency in mhz. table 1. sw frequency vs r t value f sw (mhz) r t (k) 0.2 232 0.3 150 0.4 110 0.5 88.7 0.6 71.5 0.7 60.4 0.8 52.3 1.0 41.2 1.2 33.2 14 28.0 1.6 23.7 1.8 20.5 2.0 18.2 2.2 15.8 operating frequency selection and trade-offs selection of the operating frequency is a trade-off between efficiency, component size, and input voltage range. the advantage of high frequency operation is that smaller induc - tor and capacitor values may be used. the disadvantages are lower efficiency and a smaller input voltage range. the highest switching frequency (f sw(max) ) for a given application can be calculated as follows: f sw(max) = v out + v sw(bot) t on(min) v in C v sw(top) + v sw(bot) ( ) (4) where v in is the typical input voltage, v out is the output voltage, v sw(top) and v sw(bot) are the internal switch drops (~0.42v , ~0.21 v, respectively at maximum load) and t on(min) is the minimum top switch on-time ( see the electrical characteristics). this equation shows that a slower switching frequency is necessary to accommodate a high v in /v out ratio. for transient operation, v in may go as high as the abso- lute maximum rating of 42 v regardless of the r t value, however the lt8610a/lt8610ab will reduce switching frequency as necessary to maintain control of inductor current to assure safe operation. the lt8610a/lt8610ab is capable of a maximum duty cycle of greater than 99%, and the v in -to-v out dropout is limited by the r ds(on) of the top switch. in this mode the lt8610a/lt8610ab skips switch cycles, resulting in a lower switching frequency than programmed by rt . for applications that cannot allow deviation from the pro - grammed switching frequency at low v in /v out ratios use the following formula to set switching frequency: v in(min) = v out + v sw(bot) 1C f sw ? t off(min) C v sw(bot) + v sw(top) (5) where v in(min) is the minimum input voltage without skipped cycles, v out is the output voltage, v sw(top) and v sw(bot) are the internal switch drops (~0.42v, ~0.21v, respectively at maximum load), f sw is the switching fre- quency ( set by rt ), and t off(min) is the minimum switch off- time. note that higher switching frequency will increase the minimum input voltage below which cycles will be dropped to achieve higher duty cycle. inductor selection and maximum output current the lt8610a/lt8610ab is designed to minimize solution size by allowing the inductor to be chosen based on the output load requirements of the application. during over- load or short-circuit conditions the lt8610a/lt8610ab safely tolerates operation with a saturated inductor through the use of a high speed peak-current mode architecture. a good first choice for the inductor value is: l = v out + v sw(bot) f sw (6) where f sw is the switching frequency in mhz, v out is the output voltage, v sw(bot) is the bottom switch drop (~0.21v) and l is the inductor value in h. to avoid overheating and poor efficiency, an inductor must be chosen with an rms current rating that is greater than the maximum expected output load of the application. in addition, the saturation current ( typically labeled i sat ) rating of the inductor must be higher than the load current plus 1/2 of in inductor ripple current: i l(peak) = i load(max) + 1 2 ? i l (7) lt8610a/lt8610ab series 8610abfa
16 for more information www.linear.com/lt8610a applications information where ?i l is the inductor ripple current as calculated in equation 9 and i load(max) is the maximum output load for a given application. as a quick example, an application requiring 1 a output should use an inductor with an rms rating of greater than 1a and an i sat of greater than 1.3 a. during long duration overload or short-circuit conditons, the inductor rms routing requirement is greater to avoid overheating of the inductor. to keep the efficiency high, the series resistance (dcr) should be less than 0.04, and the core material should be intended for high frequency applications. the lt8610a/lt8610ab limits the peak switch current in order to protect the switches and the system from overload faults. the top switch current limit (i lim ) is at least 6 a at low duty cycles and decreases linearly to 5a at dc = 0.8. the inductor value must then be sufficient to supply the desired maximum output current (i out(max) ), which is a function of the switch current limit (i lim ) and the ripple current. i out(max) = i lim C ? i l 2 (8) the peak-to-peak ripple current in the inductor can be calculated as follows: ? i l = v out l ? f sw ? 1C v out v in(max) ? ? ? ? ? ? (9) where f sw is the switching frequency of the lt8610a/ lt8610ab, and l is the value of the inductor. therefore, the maximum output current that the lt8610a/lt8610ab will deliver depends on the switch current limit, the induc - tor value , and the input and output voltages. the inductor value may have to be increased if the inductor ripple cur- rent does not allow sufficient maximum output current (i out(max) ) given the switching frequency, and maximum input voltage used in the desired application. the optimum inductor for a given application may differ from the one indicated by this design guide. a larger value inductor provides a higher maximum load current and reduces the output voltage ripple. for applications requiring smaller load currents, the value of the inductor may be lower and the lt8610a/lt8610ab may operate with higher ripple current. this allows use of a physically smaller inductor, or one with a lower dcr resulting in higher efficiency. be aware that low inductance may result in discontinuous mode operation, which further reduces maximum load current. inductor value has a very strong effect on burst mode ef - ficiency. larger value inductors allow more charge to be transferred to the output per pulse, which increases both efficiency and output voltage ripple. this dependence on inductance is stronger for the lt8610ab than it is for the lt8610a. if higher efficiency is needed in a burst mode ap - plication, increasing inductor value can be a quick solution. for more information about maximum output current and discontinuous operation, see linear technologys application note 44. finally, for duty cycles greater than 50% (v out /v in > 0.5), a minimum inductance is required to avoid sub-harmonic oscillation. see application note 19. input capacitor bypass the input of the lt8610a/lt8610ab circuit with a ceramic capacitor of x7r or x5r type placed as close as possible to the v in and pgnd pins. y5v types have poor performance over temperature and applied voltage, and should not be used. a 4.7 f to 10 f ceramic capacitor is adequate to bypass the lt8610a/lt8610ab and will easily handle the ripple current. note that larger input capacitance is required when a lower switching frequency is used. if the input power source has high impedance, or there is significant inductance due to long wires or cables, additional bulk capacitance may be necessary. this can be provided with a low performance electrolytic capacitor. step- down regulators draw current from the input supply in pulses with very fast rise and fall times. the input capaci - tor is required to reduce the resulting voltage ripple at the lt8610a/lt8610ab and to force this very high frequency switching current into a tight local loop, minimizing emi. a 4.7 f capacitor is capable of this task, but only if it is placed close to the lt8610 a/ lt8610ab ( see the pcb layout section). a second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the lt8610a/lt8610ab. a ceramic input capacitor combined lt8610a/lt8610ab series 8610abfa
17 for more information www.linear.com/lt8610a applications information with trace or cable inductance forms a high quality (under damped) tank circuit. if the lt8610a/lt8610ab circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the lt8610a/ lt8610abs voltage rating. this situation is easily avoided (see linear technology application note 88). output capacitor and output ripple the output capacitor has two essential functions. along with the inductor, it filters the square wave generated by the lt8610a/lt8610ab to produce the dc output. in this role it determines the output ripple, thus low impedance at the switching frequency is important. the second function is to store energy in order to satisfy transient loads and stabilize the lt8610a/lt8610abs control loop. ceramic capacitors have very low equivalent series resistance ( esr) and provide the best ripple performance. for good starting values, see the typical applications section. use x5r or x7r types. this choice will provide low output ripple and good transient response. transient performance can be improved with a higher value output capacitor and the addition of a feedforward capacitor placed between v out and fb. increasing the output capacitance will also decrease the output voltage ripple. a lower value of output capacitor can be used to save space and cost but transient performance will suffer and may cause loop instability. see the typical applications in this data sheet for suggested capacitor values. when choosing a capacitor, special attention should be given to the data sheet to calculate the effective capacitance under the relevant operating conditions of voltage bias and temperature. a physically larger capacitor or one with a higher voltage rating may be required. ceramic capacitors ceramic capacitors are small, robust and have very low esr. however, ceramic capacitors can cause problems when used with the lt8610a/lt8610ab due to their piezoelectric nature. when in burst mode operation, the lt8610a/lt8610abs switching frequency depends on the load current, and at very light loads the lt8610a/ lt8610ab can excite the ceramic capacitor at audio fre - quencies, generating audible noise. since the lt8610a/ lt8610ab operates at a lower current limit during burst mode operation, the noise is typically very quiet to a ca - sual ear. if this is unacceptable, use a high performance tantalum or electrolytic capacitor at the output . low noise ceramic capacitors are also available. a final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the lt8610 a/ lt8610ab. as previously mentioned , a ceramic input capacitor combined with trace or cable inductance forms a high quality ( un- derdamped) tank circuit. if the lt8610a/lt8610ab circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the lt8610a/ lt8610abs rating. this situation is easily avoided (see linear technology application note 88). enable pin the lt8610a/lt8610ab is in shutdown when the en pin is low and active when the pin is high. the rising threshold of the en comparator is 1.0 v, with 40 mv of hysteresis. the en pin can be tied to v in if the shutdown feature is not used, or tied to a logic level if shutdown control is required. adding a resistor divider from v in to en programs the lt8610a/lt8610ab to regulate the output only when v in is above a desired voltage ( see the block diagram). typi- cally, this threshold, v in(en) , is used in situations where the input supply is current limited, or has a relatively high sour ce resistance. a switching regulator draws constant power from the source, so source current increases as source voltage drops. this looks like a negative resistance load to the source and can cause the source to current limit or latch low under low source voltage conditions. the v in(en) threshold prevents the regulator from operating at source voltages where the problems might occur. this threshold can be adjusted by setting the values r3 and r4 such that they satisfy the following equation: v in(en) = r3 r4 + 1 ? ? ? ? ? ? ?1.0v (10) where the lt8610a/lt8610ab will remain off until v in is above v in(en) . due to the comparators hysteresis, switch- ing will not stop until the input falls slightly below v in(en) . lt8610a/lt8610ab series 8610abfa
18 for more information www.linear.com/lt8610a applications information when operating in burst mode operation for light load currents, the current through the v in(en) resistor network can easily be greater than the supply current consumed by the lt8610a/lt8610ab. therefore, the v in(en) resis- tors should be large to minimize their effect on efficiency at low loads. int v cc regulator an internal low dropout ( ldo) regulator produces the 3.4 v supply from v in that powers the drivers and the internal bias circuitry. the intv cc can supply enough current for the lt8610a/lt8610abs circuitry and must be bypassed to ground with a minimum of 1 f ceramic capacitor. good bypassing is necessary to supply the high transient currents required by the power mosfet gate drivers. to improve efficiency the internal ldo can also draw current from the bias pin when the bias pin is at 3.1 v or higher. typically the bias pin can be tied to the output of the lt8610a/ lt8610ab, or can be tied to an external supply of 3.3 v or above. if bias is connected to a supply other than v out , be sure to bypass with a local ceramic capacitor. if the bias pin is below 3.0 v, the internal ldo will consume current from v in . applications with high input voltage and high switching frequency where the internal ldo pulls current from v in will increase die temperature because of the higher power dissipation across the ldo. do not connect an external load to the intv cc pin. output voltage tracking and soft-start t he lt8610 a/ lt8610ab allows the user to program its out - put voltage ramp rate by means of the tr/ ss pin. an internal 2.2a pulls up the tr/ss pin to intv cc . putting an external capacitor on tr / ss enables soft starting the output to prevent current surge on the input supply. during the soft- start ramp the output voltage will proportionally track the tr/ss pin voltage. for output tracking applications, tr /ss can be externally driven by another voltage source. from 0v to 0.97v , the tr/ ss voltage will override the internal 0.97 v reference input to the error amplifier, thus regulating the fb pin voltage to that of tr/ss pin. in the fixed output voltage options the output voltage will track the tr/ ss pin voltage based on a factor set by the internal feedback resistor divider. the 3.3 v output options will track to a voltage 3.4 times that of the tr/ss pin, while the 5 v output options will track to a voltage 5.15 times that of the tr/ss pin. when tr/ss is above 0.97 v, tracking is disabled and the feedback voltage will regulate to the internal reference voltage. the tr/ss pin may be left floating if the function is not needed. an active pull-down circuit is connected to the tr/ss pin which will discharge the external soft-start capacitor in the case of fault conditions and restart the ramp when the faults are cleared. fault conditions that clear the soft-start capacitor are the en/uv pin transitioning low, v in voltage falling too low, or thermal shutdown. output power good when the lt8610a/lt8610abs output voltage is within the 9% window of the regulation point, which is a v fb voltage in the range of 0.883 v to 1.057v ( typical), the output voltage is considered good and the open-drain pg pin goes high impedance and is typically pulled high with an external resistor. otherwise, the internal pull- down device will pull the pg pin low. to prevent glitching both the upper and lower thresholds include 1.3% of hysteresis. this 9% power good window around the regulation point is the same for the fixed output options, which for the 3.3v output version corresponds to a 3.003 v to 3.597 v range (typical) and for the 5 v output version corresponds to a 4.55v to 5.45v range (typical). the pg pin is also actively pulled low during several fault conditions: en/uv pin is below 1 v, intv cc has fallen too low, v in is too low, or thermal shutdown. synchronization to select low ripple burst mode operation, tie the sync pin below 0.4v ( this can be ground or a logic low output). to synchronize the lt8610a/lt8610ab oscillator to an external frequency connect a square wave (with 20% to 80% duty cycle) to the sync pin. the square wave am - plitude should have valleys that are below 0.4 v and peaks above 2.4v (up to 6v). the lt8610a/lt8610ab will not enter burst mode opera - tion at low output loads while synchronized to an external clock, but instead will pulse skip to maintain regulation. the lt8610a/lt8610ab may be synchronized over a 200khz lt8610a/lt8610ab series 8610abfa
19 for more information www.linear.com/lt8610a applications information figure 3. reverse v in protection v in v in d1 lt8610a/ lt8610ab en/uv 8610ab f03 gnd to 2.2 mhz range. the r t resistor should be chosen to set the lt8610a/lt8610ab switching frequency equal to or below the lowest synchronization input. for example, if the synchronization signal will be 500 khz and higher, the r t should be selected for 500 khz. the slope compensation is set by the r t value, while the minimum slope compensation required to avoid subharmonic oscillations is established by the inductor size, input voltage, and output voltage. since the synchronization frequency will not change the slopes of the inductor current waveform, if the inductor is large enough to avoid subharmonic oscillations at the frequency set by r t , then the slope compensation will be sufficient for all synchronization frequencies. for some applications it is desirable for the lt8610 a/ lt8610ab to operate in pulse- skipping mode, offering two major differences from burst mode operation. first is the clock stays awake at all times and all switching cycles are aligned to the clock. second is that full switching frequency is reached at lower output load than in burst mode operation. these two differences come at the expense of increased quiescent current. to enable pulse- skipping mode, the sync pin is tied high either to a logic output or to the intv cc pin. the lt8610a/lt8610ab does not operate in forced con- tinuous mode regardless of sync signal. never leave the sync pin floating. shorted and reversed input protection the lt8610a/lt8610ab will tolerate a shorted output. several features are used for protection during output short-circuit and brownout conditions. the first is the switching frequency will be folded back while the output is lower than the set point to maintain inductor current control. second, the bottom switch current is monitored such that if inductor current is beyond safe levels switch - ing of the top switch will be delayed until such time as the inductor current falls to safe levels. frequency foldback behavior depends on the state of the sync pin: if the sync pin is low the switching frequency will slow while the output voltage is lower than the pro - grammed level . if the sync pin is connected to a clock source or tied high, the lt8610a/lt8610ab will stay at the programmed frequency without foldback and only slow switching if the inductor current exceeds safe levels. there is another situation to consider in systems where the output will be held high when the input to the lt8610a/ lt8610ab is absent. this may occur in battery charging applications or in battery-backup systems where a battery or some other supply is diode ored with the lt8610a/ lt8610abs output. if the v in pin is allowed to float and the en pin is held high ( either by a logic signal or because it is tied to v in ), then the lt8610a/lt8610abs internal circuitry will pull its quiescent current through its sw pin. this is acceptable if the system can tolerate several a in this state. if the en pin is grounded the sw pin current will drop to near 1 a. however, if the v in pin is grounded while the output is held high, regardless of en, parasitic body diodes inside the lt8610a/lt8610ab can pull current from the output through the sw pin and the v in pin. figure 3 shows a connection of the v in and en/uv pins that will allow the lt8610a/lt8610ab to run only when the input voltage is present and that protects against a shorted or reversed input. pcb layout for proper operation and minimum emi, care must be taken during printed circuit board layout. figure 4 shows the recommended component placement with trace, ground plane and via locations. note that large, switched currents flow in the lt8610a/lt8610abs v in pins, gnd pins, and the input capacitor ( c 1). the loop formed by the input capacitor should be as small as possible by placing the capacitor adjacent to the v in and gnd pins. when using a physically large input capacitor the resulting loop may become too large in which case using a small case/value capacitor placed close to the v in and gnd pins plus a larger capacitor further away is preferred. these components, along with the inductor and output capacitor, should be placed on the same side of the circuit board, and their connections should be made on that layer. place a local , unbroken ground plane under the application circuit on lt8610a/lt8610ab series 8610abfa
20 for more information www.linear.com/lt8610a figure 4. recommended pcb layout for the lt8610a/lt8610ab v out 8610ab f04 outline of local ground plane sw bst bias intv cc gnd 9 10 11 12 13 14 15 pg fb gnd v out 16 sync tr/ss rt en/uv v in 1 2 3 4 5 6 7 8 v out line to bias vias to ground plane the layer closest to the surface layer. the sw and boost nodes should be as small as possible. finally, keep the fb and rt nodes small so that the ground traces will shield them from the sw and boost nodes. the exposed pad on the bottom of the package must be soldered to ground so that the pad is connected to ground electrically and also acts as a heat sink thermally. to keep thermal resistance low, extend the ground plane as much as possible, and add thermal vias under and near the lt8610a/lt8610ab to additional ground planes within the circuit board and on the bottom side. unlike the lt8610, the lt8610a/ lt8610ab has pin 7 as an nc ( no connect) pin. this pin can be soldered to gnd to have an lt8610 compatible pcb layout. alternatively, pin 7 applications information can be left unconnected to help meet pcb clearance and creepage requirements between the v in and gnd traces. high temperature considerations for higher ambient temperatures, care should be taken in the layout of the pcb to ensure good heat sinking of the lt8610a/lt8610ab. the exposed pad on the bottom of the package must be soldered to a ground plane. this ground should be tied to large copper layers below with thermal vias; these layers will spread heat dissipated by the lt8610 a/ lt8610ab. placing additional vias can reduce thermal resistance further. the maximum load current should be derated as the ambient temperature approaches the maximum junction rating. power dissipation within the lt8610a/lt8610ab can be estimated by calculating the total power loss from an efficiency measurement and sub - tracting the inductor loss. the die temperature is calculated by multiplying the lt8610a/lt8610ab power dissipation by the thermal resistance from junction to ambient. the lt8610a/lt8610ab will stop switching and indicate a fault condition if safe junction temperature is exceeded. temperature rise of the lt8610a/lt8610ab is worst when operating at high load, high v in , and high switching frequency. if the case temperature is too high for a given application, then either v in , switching frequency, or load current can be decreased to reduce the temperature to an acceptable level. figure 5 shows an example of how case temperature can be managed by reducing v in , switching frequency, or load. figure 5. lt8610ab case temperature rise input voltage (v) case temperature rise (c) 120 140 16 24 36 8610ab f05 80 20 40 0 100 60 8 12 20 28 32 f sw = 2mhz i load = 2.5a f sw = 2mhz i load = 3.5a t a = 25c f sw = 1mhz i load = 3.5a lt8610a/lt8610ab series 8610abfa
21 for more information www.linear.com/lt8610a typical applications bst v in en/uv sync intv cc tr/ss rt sw lt8610a/ lt8610ab gnd bias 8610ab ta02 pg fb 0.1f v out 5v 3.5a 4.7f v in 5.5v to 42v 1f 10nf 4.7pf 2.2h 1m 243k f sw = 2mhz l: xal 5030 18.2k 47f* 1210 x7r power good 100k 5v 2mhz step-down converter 5v step-down converter *consider doubling output capacitance for lt8610ab if application requires low output voltage ripple in burst mode operation. 12v step-down converter l: ihlp-2525cz-01 bst v in en/uv sync intv cc tr/ss rt sw lt8610a-5 gnd bias 8610ab ta03 v out 0.1f v out 12v 3.5a 4.7f v in 3.8v to 42v 1f 10nf 10h f sw = 400khz 110k 100f 1210 x5r pg power good 100k bst v in en/uv sync intv cc tr/ss rt sw lt8610a/ lt8610ab gnd bias 8610ab ta09 pg fb 0.1f v out 12v 3.5a 4.7f v in 12.5v to 42v 1f 10nf 10pf 10h 1m 88.7k f sw = 1mhz 41.2k 47f* 1210 x7r power good 100k l: ihlp-2525cz-01 lt8610a/lt8610ab series 8610abfa
22 for more information www.linear.com/lt8610a typical applications 1.8v 2mhz step-down converter *consider doubling output capacitance for lt8610ab if application requires low output voltage ripple in burst mode operation. bst v in en/uv sync pg intv cc tr/ss rt sw lt8610a/ lt8610ab gnd bias 8610ab ta06 fb 0.1f v out 1.8v 3.5a 4.7f v in 3.4v to 15v (42v transient) 1f 10nf 4.7pf 1h 866k 1m f sw = 2mhz 18.2k 100f* 1210 x5r l: ihlp-2020bz-01 3.3v 2mhz step-down converter bst v in en/uv sync pg intv cc tr/ss rt sw lt8610a/ lt8610ab gnd bias 8610ab ta04 fb 0.1f v out 3.3v 3.5a 4.7f v in 3.8v to 27v (42v transient) 1f 10nf 4.7pf 2.2h 1m 412k f sw = 2mhz 18.2k 47f* 1210 x7r l: xal 5030 1.8v step-down converter bst v in en/uv sync pg intv cc tr/ss rt sw lt8610a/ lt8610ab gnd bias 8610ab ta07 fb 0.1f v out 1.8v 3.5a 4.7f v in 3.4v to 42v 1f 10nf 4.7pf 4.7h 866k 1m f sw = 400khz 110k 47f* 3 1210 x7r l: ihlp-2020bz-01 lt8610a/lt8610ab series 8610abfa
23 for more information www.linear.com/lt8610a typical applications 3.3v step-down converter ultralow emi 5v 2.5a step-down converter l: ihlp-2525bd-01 bst v in en/uv pg sync intv cc tr/ss rt sw lt8610a-3.3 gnd bias 8610ab ta05 v out 0.1f v out 3.3v 3.5a 4.7f v in 3.8v to 42v 1f 10nf 8.2h f sw = 400khz 110k 100f 1210 x5r bst v in en/uv pg sync intv cc tr/ss rt sw lt8610a/ lt8610ab gnd bias 8610ab ta11 fb 0.1f v out 5v 3.5a 4.7f v in 5.5v to 42v 1f 10nf 10pf 4.7h 4.7h 1m fb1 bead 243k f sw = 800khz 52.3k 4.7f 4.7f 47f* 1210 x7r fb1: tdk mpz2012s101a l: ihlp-2020bz-01 *consider doubling output capacitance for lt8610ab if application requires low output voltage ripple in burst mode operation. lt8610a/lt8610ab series 8610abfa
24 for more information www.linear.com/lt8610a package description please refer to http://www .linear.com/designtools/packaging/ for the most recent package drawings. msop (mse16) 0213 rev f 0.53 0.152 (.021 .006) seating plane 0.18 (.007) 1.10 (.043) max 0.17 ?0.27 (.007 ? .011) typ 0.86 (.034) ref 0.50 (.0197) bsc 16 16151413121110 1 2 3 4 5 6 7 8 9 9 1 8 note: 1. dimensions in millimeter/(inch) 2. drawing not to scale 3. dimension does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.152mm (.006") per side 4. dimension does not include interlead flash or protrusions. interlead flash or protrusions shall not exceed 0.152mm (.006") per side 5. lead coplanarity (bottom of leads after forming) shall be 0.102mm (.004") max 6. exposed pad dimension does include mold flash. mold flash on e-pad shall not exceed 0.254mm (.010") per side. 0.254 (.010) 0 ? 6 typ detail ?a? detail ?a? gauge plane 5.10 (.201) min 3.20 ? 3.45 (.126 ? .136) 0.889 0.127 (.035 .005) recommended solder pad layout 0.305 0.038 (.0120 .0015) typ 0.50 (.0197) bsc bottom view of exposed pad option 2.845 0.102 (.112 .004) 2.845 0.102 (.112 .004) 4.039 0.102 (.159 .004) (note 3) 1.651 0.102 (.065 .004) 1.651 0.102 (.065 .004) 0.1016 0.0508 (.004 .002) 3.00 0.102 (.118 .004) (note 4) 0.280 0.076 (.011 .003) ref 4.90 0.152 (.193 .006) detail ?b? detail ?b? corner tail is part of the leadframe feature. for reference only no measurement purpose 0.12 ref 0.35 ref mse package 16-lead plastic msop, exposed die pad (reference ltc dwg # 05-08-1667 rev f) lt8610a/lt8610ab series 8610abfa
25 for more information www.linear.com/lt8610a 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 representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. revision history rev date description page number a 08/14 added fixed output options. clarified applications information. 1 - 4, 10, 12, 13 14, 18 lt8610a/lt8610ab series 8610abfa
26 for more information www.linear.com/lt8610a ? linear technology corporation 2013 lt 0814 rev a ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com/lt8610a related parts typical application 3.3v and 1.8v with ratio tracking ultralow i q 2.5v, 3.3v step-down with ldo bst v in en/uv sync pg intv cc tr/ss rt sw lt8610a/ lt8610ab gnd bias fb 0.1f v out1 3.3v 3.5a 4.7f v in 3.8v to 42v 1f 10nf 4.7pf 5.6h 232k 97.6k f sw = 500khz 88.7k bst v in en/uv sync pg intv cc tr/ss rt sw lt8610a/ lt8610ab gnd bias 8610ab ta08 fb 0.1f v out2 1.8v 3.5a 4.7f 1f 4.7pf 3.3h 80.6k 24.3k 93.1k f sw = 500khz 88.7k 10k 100f* 1210 x5r 47f* 1210 x7r l: ihlp-2020cz-01, 5.6h l: ihlp-2020cz-01, 3.3h bst v in en/uv sync pg intv cc tr/ss rt sw lt8610ab-3.3 gnd bias 8610ab ta10 v out 0.1f v out1 3.3v 3.5a 4.7f v in 3.8v to 27v 1f 10nf 2.2h 2.2f v out2 2.5v 20ma f sw = 2mhz 18.2k 47f 2 1210 x7r in lt3008-2.5 shdn out sense l: ihlp-2020bz-01 part number description comments lt8610 42v, 2.5a, 96% efficiency, 2.2mhz synchronous micropower step-down dc/dc converter with i q = 2.5a v in : 3.4v to 42v, v out(min) = 0.97v, i q = 2.5a, i sd < 1a, msop-16e package lt8614 42v, 2.5a with 4a, 96% efficiency, 2.2mhz synchronous micropower step-down dc/dc converter with i q = 2.5a v in : 3.4v to 42v, v out(min) = 0.97v, i q = 2.5a, i sd < 1a, 3mm 6mm qfn-28 package lt8611 42v, 2.5a, 96% efficiency, 2.2mhz synchronous micropower step-down dc/dc converter with i q = 2.5a and input/output current limit/monitor v in : 3.4v to 42v, v out(min) = 0.97v, i q = 2.5a, i sd < 1a, 3mm 5mm qfn-24 package lt3690 36v with 60v transient protection, 4a, 92% efficiency, 1.5mhz synchronous micropower step-down dc/dc converter with i q = 70a v in : 3.9v to 36v, v out(min) = 0.985v, i q = 70a, i sd < 1a, 4mm 6mm qfn-26 package lt3971 38v, 1.2a, 2.2mhz high efficiency micropower step-down dc/dc converter with i q = 2.8a v in : 4.2v to 38v, v out(min) = 1.21v, i q = 2.8a, i sd < 1a, 3mm 3mm dfn-10 and msop-10e packages lt3970 40v, 350ma, 2.2mhz high efficiency micropower step-down dc/dc converter with i q = 2.5a v in : 4.2v to 40v, v out(min) = 1.21v, i q = 2.5a, i sd < 1a, 3mm 2mm dfn-10 and msop-10 packages lt3990 62v, 350ma, 2.2mhz high efficiency micropower step-down dc/dc converter with i q = 2.5a v in : 4.2v to 62v, v out(min) = 1.21v, i q = 2.5a, i sd < 1a, 3mm 3mm dfn-10 and msop-6e packages lt3480 36v with transient protection to 60v, 2a (i out ), 2.4mhz, high efficiency step-down dc/dc converter with burst mode operation v in : 3.6v to 36v, transient to 60v, v out(min) = 0.78v, i q = 70a, i sd < 1a, 3mm 3mm dfn-10 and msop-10e packages lt 3980 58v with t ransient protection to 80v, 2a (i out ), 2.4mhz, high efficiency step-down dc/dc converter with burst mode operation v in : 3.6v to 58v, transient to 80v, v out(min) = 0.78v, i q = 85a, i sd < 1a, 3mm 4mm dfn-16 and msop-16e packages *consider doubling output capacitance for lt8610ab if application requires low output voltage ripple in burst mode operation. lt8610a/lt8610ab series 8610abfa

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