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general description the max5035 easy-to-use, high-efficiency, high-volt- age, step-down dc-dc converter operates from an input voltage up to 76v and consumes only 270a qui- escent current at no load. this pulse-width modulated (pwm) converter operates at a fixed 125khz switching frequency at heavy loads, and automatically switches to pulse-skipping mode to provide low quiescent cur- rent and high efficiency at light loads. the max5035 includes internal frequency compensation simplifying circuit implementation. the device uses an internal low- on-resistance, high-voltage, dmos transistor to obtain high efficiency and reduce overall system cost. this device includes undervoltage lockout, cycle-by-cycle current limit, hiccup mode output short-circuit protec- tion, and thermal shutdown. the max5035 delivers up to 1a output current. the out- put current may be limited by the maximum power dis- sipation capability of the package. external shutdown is included, featuring 10a (typ) shutdown current. the max5035a/b/c versions have fixed output voltages of 3.3v, 5v, and 12v, respectively, while the max5035d/e versions have an adjustable output voltage from 1.25v to 13.2v. the max5035 is available in space-saving 8-pin so and 8-pin plastic dip packages and operates over the automotive (-40c to +125c) temperature range. applications automotive consumer electronics industrial distributed power features wide 7.5v to 76v input voltage range fixed (3.3v, 5v, 12v) and adjustable (1.25v to 13.2v) versions 1a output current efficiency up to 94% internal 0.4? high-side dmos fet 270 a quiescent current at no load, 10 a shutdown current internal frequency compensation fixed 125khz switching frequency thermal shutdown and short-circuit current limit 8-pin so and pdip packages max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter ________________________________________________________________ maxim integrated products 1 ordering information 19-2988; rev 5; 5/11 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. evaluation kit available part temp range pin- package ou tpu t vo lta ge ( v) max5035ausa 0c to +85c 8 so max5035aupa 0c to +85c 8 pdip max5035aasa -40c to +125c 8 so m ax 5035aas a/v + -40c to +125c 8 so 3.3 max5035busa 0c to +85c 8 so max5035bupa 0c to +85c 8 pdip max5035basa -40c to +125c 8 so m ax 5035bas a/v + -40c to +125c 8 so 5.0 1 2 3 4 bst vd sgnd fb 8 7 6 5 lx top view v in gnd on/off max5035 so/pdip pin configuration max5035 gnd bst lx v in sgnd fb d1 50sq100 vd 100 h v out 5v v in 7.5v to 76v 68 f 0.1 f 0.1 f 68 f on off r1 r2 on/off typical operating circuit /v denotes an automotive qualified part. + denotes a lead(pb)-free/rohs-compliant package. ordering information continued at end of data sheet.
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter 2 _______________________________________________________________________________________ absolute maximum ratings stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. (voltages referenced to gnd, unless otherwise specified.) v in .........................................................................-0.3v to +80v sgnd ....................................................................-0.3v to +0.3v lx.................................................................-0.8v to (v in + 0.3v) bst ...............................................................-0.3v to (v in + 10v) bst (transient < 100ns) ................................-0.3v to (v in + 15v) bst to lx................................................................-0.3v to +10v bst to lx (transient < 100ns) ................................-0.3v to +15v on/ off ..................................................................-0.3v to +80v vd...........................................................................-0.3v to +12v fb max5035a/max5035b/max5035c ...................-0.3v to +15v max5035d/e ......................................................-0.3v to +12v v out short-circuit duration (v in 40v)........................indefinite vd short-circuit duration ..............................................indefinite continuous power dissipation (t a = +70c) 8-pin pdip (derate 9.1mw/c above +70c)...............727mw 8-pin so (derate 5.9mw/ c above +70 c)..................471mw operating temperature range max5035_u_ _ ...................................................0 c to +85c max5035_a_ _ ..............................................-40 c to +125c storage temperature range .............................-65 c to +150c junction temperature ......................................................+150c lead temperature (soldering, 10s) .................................+300c soldering temperature (reflow) lead(pb)-free...............................................................+260c containing lead(pb) .....................................................+240c electrical characteristics (max5035_u_ _) (v in = +12v, v on/ off = +12v, i out = 0, t a = 0c to +85c , unless otherwise noted. typical values are at t a = +25c. see the typical application circuit. ) parameter symbol conditions min typ max units max5035a 7.5 76.0 max5035b 7.5 76.0 max5035c 15 76 input voltage range v in max5035d/e 7.5 76.0 v undervoltage lockout uvlo 5.2 v max5035a v in = 7.5v to 76v, i out = 20ma to 1a 3.185 3.3 3.415 max5035b v in = 7.5v to 76v, i out = 20ma to 1a 4.85 5.0 5.15 output voltage v out max5035c v in = 15v to 76v, i out = 20ma to 1a 11.64 12 12.36 v v in = 7.5v to 76v, max5035d/e 1.192 1.221 1.250 feedback voltage v fb v in = 7.5v to 76v, max5035e 1.185 1.221 1.250 v v in = 12v, i load = 0.5a, max5035a 86 v in = 12v, i load = 0.5a, max5035b 90 v in = 24v, i load = 0.5a, max5035c 94 efficiency v in = 12v, v out = 5v, i load = 0.5a, max5035d/e 90 % v fb = 3.5v, v in = 7.5v to 76v, max5035a 270 440 v fb = 5.5v, v in = 7.5v to 76v, max5035b 270 440 v fb = 13v, v in = 15v to 76v, max5035c 270 440 v fb = 1.3v, max5035d 270 440 quiescent supply current i q v fb = 1.3v, max5035e 340 460 a shutdown current i shdn v on/ off = 0v, v in = 7.5v to 76v 10 45 a peak switch current limit i lim (note 1) 1.30 1.9 2.50 a
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter _______________________________________________________________________________________ 3 electrical characteristics (continued) (max5035_u_ _) (v in = +12v, v on/ off = +12v, i out = 0, t a = 0c to +85c , unless otherwise noted. typical values are at t a = +25c. see the typical application circuit. ) parameter symbol conditions min typ max units switch leakage current i ol v in = 76v, v on/ off = 0v, v lx = 0v 0.01 1 a switch on-resistance r ds ( on ) i switch = 1a 0.40 0.80 ? pfm threshold i pfm minimum switch current in any cycle 55 85 130 ma fb input bias current i b max5035d/e -150 +0.01 +150 na on/ off control input rising trip point for max5035a/b/c/d 1.53 1.69 1.85 on/ off input-voltage threshold v on/ off rising trip point for max5035e 1.40 1.65 1.90 v on/ off input-voltage hysteresis v hyst 100 mv on/ off input current i on/ off v on/ off = 0v to v in 10 150 na on/ off operating voltage range v on/ off 76 v oscillator oscillator frequency f osc 109 125 135 khz maximum duty cycle d max max5035d/e 95 % voltage regulator regulator output voltage vd v in = 8.5v to 76v, i l = 0 6.9 7.8 8.8 v dropout voltage 7.5v v in 8.5v, i l = 1ma 2.0 v load regulation ? vd/ ? i vd 0 to 5ma 150 ? package thermal characteristics so package (jedec 51) 170 thermal resistance (junction to ambient) ja dip package (jedec 51) 110 c/w thermal shutdown thermal-shutdown junction temperature t sh +160 c thermal-shutdown hysteresis t hyst 20 c electrical characteristics (max5035_a_ _) (v in = +12v, v on/ off = +12v, i out = 0, t a = t j = -40c to +125c , unless otherwise noted. typical values are at t a = +25c. see the typical application circuit. ) (note 2) parameter symbol conditions min typ max units max5035a 7.5 76.0 max5035b 7.5 76.0 max5035c 15 76 input voltage range v in max5035d/e 7.5 76.0 v undervoltage lockout uvlo 5.2 v max5035a v in = 7.5v to 76v, i out = 20ma to 1a 3.185 3.3 3.415 max5035b v in = 7.5v to 76v, i out = 20ma to 1a 4.825 5.0 5.175 output voltage v out max5035c v in = 15v to 76v, i out = 20ma to 1a 11.58 12 12.42 v
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter 4 _______________________________________________________________________________________ electrical characteristics (max5035_a_ _) (continued) (v in = +12v, v on/ off = +12v, i out = 0, t a = t j = -40c to +125c , unless otherwise noted. typical values are at t a = +25c. see the typical application circuit. ) (note 2) parameter symbol conditions min typ max units v in = 7.5v to 76v, max5035d 1.192 1.221 1.250 feedback voltage v fb v in = 7.5v to 76v, max5035e 1.185 1.221 1.250 v v in = 12v, i load = 0.5a, max5035a 86 v in = 12v, i load = 0.5a, max5035b 90 v in = 24v, i load = 0.5a, max5035c 94 efficiency v in = 12v, v out = 5v, i load = 0.5a, max5035d/e 90 % v fb = 3.5v, v in = 7.5v to 76v, max5035a 270 440 v fb = 5.5v, v in = 7.5v to 76v, max5035b 270 440 v fb = 13v, v in = 15v to 76v, max5035c 270 440 v fb = 1.3v, max5035d 270 440 quiescent supply current i q v fb = 1.3v, max5035e 340 460 a shutdown current i shdn v on/ off = 0v, v in = 7.5v to 76v 10 45 a peak switch current limit i lim (note 1) 1.30 1.9 2.50 a v in = 76v, v on/ off = 0v, v lx = 0v 1 switch leakage current i ol v in = 76v, v on/ off = 0v, v lx = 0v, max5035e 5 a switch on-resistance r ds ( on ) i switch = 1a 0.40 0.80 ? pfm threshold i pfm minimum switch current in any cycle 55 85 130 ma fb input bias current i b max5035d/e -150 +0.01 +150 na on/ off control input rising trip point for max5035a/b/c/d 1.50 1.69 1.85 on/ off input-voltage threshold v on/ off rising trip point for max5035e 1.40 1.65 1.90 v on/ off input-voltage hysteresis v hyst 100 mv on/ off input current i on/ off v on/ off = 0v to v in 10 150 na on/ off operating voltage range v on/ off 76 v oscillator oscillator frequency f osc 105 125 137 khz maximum duty cycle d max max5035d/e 95 % voltage regulator regulator output voltage vd v in = 8.5v to 76v, i l = 0 6.5 7.8 9.0 v dropout voltage 7.5v v in 8.5v, i l = 1ma 2.0 v load regulation ? vd/ ? i vd 0 to 5ma 150 ?
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter _______________________________________________________________________________________ 5 typical operating characteristics (v in = 12v, v on/ off = 12v, t a = -40 c to +125 c, unless otherwise noted. typical values are at t a = +25 c. see the typical application circuit , if applicable.) parameter symbol conditions min typ max units package thermal characteristics so package (jedec 51) 170 thermal resistance (junction to ambient) ja dip package (jedec 51) 110 c/w thermal shutdown thermal-shutdown junction temperature t sh +160 c thermal-shutdown hysteresis t hyst 20 c note 1: switch current at which current limit is activated. note 2: all limits at -40c are guaranteed by design, not production tested. v out vs. temperature (max5035aasa, v out = 3.3v) max5035 toc01 temperature ( c) v out (v) 3.24 3.28 3.32 3.36 3.40 3.20 i out = 0.1a i out = 1a 100 50 0 -50 150 -25 25 75 125 v out vs. temperature (max5035dasa, v out = 5v) max5035 toc02 temperature ( c) v out (v) 125 100 -25 0 25 50 75 4.85 4.90 4.95 5.00 5.05 5.10 5.15 5.20 4.80 -50 150 i out = 0.1a i out = 1a line regulation (max5035aasa, v out = 3.3v) max5035 toc03 input voltage (v) output voltage (v) 65 50 35 20 3.24 3.28 3.32 3.36 3.40 3.20 580 i out = 1a i out = 0.1a line regulation (max5035dasa, v out = 5v) max5035 toc04 input voltage (v) output voltage (v) 65 50 20 35 4.85 4.90 4.95 5.00 5.05 5.10 5.15 5.20 4.80 580 i out = 1a i out = 0.1a load regulation (max5035aasa, v out = 3.3v) max5035 toc05 i load (ma) v out (v) 800 600 400 200 3.24 3.28 3.32 3.36 3.40 3.20 0 1000 v in = 7.5v, 24v v in = 76v load regulation (max5035dasa, v out = 5v) max5035 toc06 i load (ma) v out (v) 800 600 400 200 4.95 5.00 5.05 5.10 4.90 01000 v in = 76v v in = 24v v in = 7.5v electrical characteristics (max5035_a_ _) (continued) (v in = +12v, v on/ off = +12v, i out = 0, t a = t j = -40c to +125c , unless otherwise noted. typical values are at t a = +25c. see the typical application circuit. ) (note 2)
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter 6 _______________________________________________________________________________________ typical operating characteristics (continued) (v in = 12v, v on/ off = 12v, t a = -40 c to +125 c, unless otherwise noted. typical values are at t a = +25 c. see the typical application circuit , if applicable.) output current limit vs. temperature max5035 toc10 temperature ( c) output current limit (a) 125 100 75 50 25 0 -25 0.5 1.0 1.5 2.0 0 -50 150 max5035dasa v out = 5v 5% drop in v out output current limit vs. input voltage max5035 toc11 input voltage (v) output current limit (a) 65 50 35 20 0.8 1.1 1.4 1.7 2.0 0.5 580 max5035dasa v out = 5v 5% drop in vout quiescent supply current vs. temperature max5035 toc12 temperature ( c) quiescent supply current ( a) 230 260 290 320 350 200 100 50 0 -50 150 -25 25 75 125 quiescent supply current vs. input voltage max5035 toc13 input voltage (v) quiescent supply current ( a) 66 56 46 36 26 16 230 260 290 320 350 200 676 shutdown current vs. temperature max5035 toc14 temperature ( c) shutdown current ( a) 5 10 15 20 25 0 100 50 0 -50 150 -25 25 75 125 shutdown current vs. input voltage max5035 toc15 input voltage (v) shutdown current ( a) 66 56 46 36 26 16 4 8 12 16 20 0 676 efficiency vs. load current (max5035aasa, v out = 3.3v) max5035 toc07 load current (ma) efficiency (%) 800 600 400 200 10 20 30 40 50 60 70 80 90 100 0 0 1000 v in = 76v v in = 48v v in = 24v v in = 12v v in = 7.5v efficiency vs. load current (max5035dasa, v out = 5v) max5035 toc08 load current (ma) efficiency (%) 800 600 400 200 10 20 30 40 50 60 70 80 90 100 0 01000 v in = 76v v in = 48v v in = 24v v in = 12v v in = 7.5v efficiency vs. load current (max5035dasa, v out = 12v) max5035 toc09 load current (ma) efficiency (%) 800 600 400 200 10 20 30 40 50 60 70 80 90 100 0 0 1000 v in = 76v v in = 48v v in = 24v v in = 15v
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter _______________________________________________________________________________________ 7 typical operating characteristics (continued) (v in = 12v, v on/ off = 12v, t a = -40 c to +125 c, unless otherwise noted. typical values are at t a = +25 c. see the typical application circuit , if applicable.) output voltage vs. input voltage max5035 toc16 v in (v) v out (v) 12 9 6 3 3 6 9 12 15 0 015 i out = 0 i out = 0.3a i out = 1a max5035dasa v out = 12v v on / off = v in max5035dasa load-transient response max5035 toc17 400 s/div b a a: v out , 200mv/div, ac-coupled b: i out , 500ma/div, 0.1a to 1a v out = 5v max5035dasa load-transient response max5035 toc18 400 s/div b a a: v out , 200mv/div, ac-coupled b: i out , 500ma/div, 0.5a to 1a v out = 5v max5035dasa load-transient response max5035 toc19 400 s/div b a a: v out , 200mv/div, ac-coupled b: i out , 500ma/div, 0.1a to 0.5a v out = 5v max5035dasa lx waveforms max5035 toc20 4 s/div b 0 a 0 a: switch voltage (lx pin), 20v/div (v in = 48v) b: inductor current, 500ma/div (i out = 1a) max5035dasa lx waveforms max5035 toc21 4 s/div b 0 a 0 a: switch voltage (lx pin), 20v/div (v in = 48v) b: inductor current, 200ma/div (i out = 100ma)
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter 8 _______________________________________________________________________________________ typical operating characteristics (continued) (v in = 12v, v on/ off = 12v, t a = -40 c to +125 c, unless otherwise noted. typical values are at t a = +25 c. see the typical application circuit , if applicable.) max5035dasa lx waveforms max5035 toc22 4 s/div b a a: switch voltage (lx pin), 20v/div (v in = 48v) b: inductor current, 200ma/div (i out = 0) 0 0 max5035dasa startup waveform (i o = 0) max5035 toc23 1ms/div b a a: v on/off , 2v/div b: v out , 2v/div 0 0 max5035dasa startup waveform (i o = 1a) max5035 toc24 1ms/div b a a: v on/off , 2v/div b: v out , 2v/div 0 0 peak switch current limit vs. input voltage max5035 toc25 input voltage (v) peak switch current limit (a) 56 66 46 36 26 16 1.0 1.5 2.0 2.5 3.0 0.5 676 max5035dasa v out = 5v 5% drop in v out
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter _______________________________________________________________________________________ 9 pin description pin name function 1 bst boost capacitor connection. connect a 0.1f ceramic capacitor from bst to lx. 2 vd internal regulator output. bypass vd to gnd with a 0.1f ceramic capacitor. 3 sgnd internal connection. sgnd must be connected to gnd. 4fb output sense feedback connection. for fixed output voltage (max5035a, max5035b, max5035c), connect fb to v out . for adjustable output voltage (max5035d, max5035e), use an external resistive voltage-divider to set v out . v fb regulating set point is 1.22v. 5 on/ off shutdown control input. pull on/ off low to put the device in shutdown mode. drive on/ off high for normal operation. 6 gnd ground 7v in input voltage. bypass v in to gnd with a low esr capacitor as close to the device as possible. 8 lx source connection of internal high-side switch enable lx bst v in on/off v ref regulator (for driver) regulator (for analog) osc ramp high-side current sense i ref-pfm i ref-lim cpfm 1.69v cilim fb x1 v ref eamp control logic cpwm vd gnd r h r l clk sgnd max5035 type 3 compensation thermal shutdown ramp block diagram
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter 10 ______________________________________________________________________________________ detailed description the max5035 step-down dc-dc converter operates from a 7.5v to 76v input voltage range. a unique volt- age-mode control scheme with voltage feed-forward and an internal switching dmos fet provides high effi- ciency over a wide input voltage range. this pulse- width modulated converter operates at a fixed 125khz switching frequency. the device also features automat- ic pulse-skipping mode to provide low quiescent cur- rent and high efficiency at light loads. under no load, the max5035 consumes only 270a, and in shutdown mode, consumes only 10a. the max5035 also fea- tures undervoltage lockout, hiccup mode output short- circuit protection, and thermal shutdown. shutdown mode drive on/ off to ground to shut down the max5035. shutdown forces the internal power mosfet off, turns off all internal circuitry, and reduces the v in supply cur- rent to 10a (typ). the on/ off rising threshold is 1.69v (typ). before any operation begins, the voltage at on/ off must exceed 1.69v (typ). the on/ off input has 100mv hysteresis. undervoltage lockout (uvlo) use the on/ off function to program the uvlo thresh- old at the input. connect a resistive voltage-divider from v in to gnd with the center node to on/ off as shown in figure 1. calculate the threshold value by using the following formula: the minimum recommended v uvlo(th) is 6.5v, 7.5v, and 13v for the output voltages of 3.3v, 5v, and 12v, respec- tively. the recommended value for r2 is less than 1m ? . if the external uvlo threshold-setting divider is not used, an internal undervoltage-lockout feature monitors the supply voltage at v in and allows operation to start when v in rises above 5.2v (typ). this feature can be used only when v in rise time is faster than 2ms. for slower v in rise time, use the resistive-divider at on/ off . boost high-side gate drive (bst) connect a flying bootstrap capacitor between lx and bst to provide the gate-drive voltage to the high-side n-channel dmos switch. the capacitor is alternately charged from the internally regulated output voltage vd and placed across the high-side dmos driver. use a 0.1f, 16v ceramic capacitor located as close to the device as possible. on startup, an internal low-side switch connects lx to ground and charges the bst capacitor to vd. once the bst capacitor is charged, the internal low-side switch is turned off and the bst capacitor voltage provides the necessary enhancement voltage to turn on the high-side switch. thermal-overload protection the max5035 features integrated thermal overload pro- tection. thermal overload protection limits total power dissipation in the device, and protects the device in the event of a fault condition. when the die temperature exceeds +160c, an internal thermal sensor signals the shutdown logic, turning off the internal power mosfet and allowing the ic to cool. the thermal sensor turns the internal power mosfet back on after the ics die tem- perature cools down to +140c, resulting in a pulsed output under continuous thermal overload conditions. applications information setting the output voltage the max5035a/b/c have preset output voltages of 3.3v, 5.0v, and 12v, respectively. connect fb to the preset output voltage (see the typical operating circuit ). the max5035d/e versions offer an adjustable output voltage. set the output voltage with a resistive voltage- divider connected from the circuits output to ground (figure 1). connect the center node of the divider to fb. choose r4 less than 15k ? , then calculate r3 as follows: r v r out 3 122 122 4 = ? (.) . v r r v uvlo th () . =+ ? ? ? ? ? ? 1 1 2 185 max5035d gnd bst lx v in sgnd fb d1 50sq100 vd 100 h v out 5v v in 7.5v to 76v 68 f 0.1 f 0.1 f c out 68 f r1 r2 r3 41.2k ? r4 13.3k ? on/off figure 1. adjustable output voltage
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter ______________________________________________________________________________________ 11 the max5035 features internal compensation for opti- mum closed-loop bandwidth and phase margin. with the preset compensation, it is strongly advised to sense the output immediately after the primary lc. inductor selection the choice of an inductor is guided by the voltage dif- ference between v in and v out , the required output current, and the operating frequency of the circuit. use an inductor with a minimum value given by: where: i outmax is the maximum output current required, and f sw is the operating frequency of 125khz. use an induc- tor with a maximum saturation current rating equal to at least the peak switch current limit (i lim ). use inductors with low dc resistance for higher efficiency. selecting a rectifier the max5035 requires an external schottky rectifier as a freewheeling diode. connect this rectifier close to the device using short leads and short pc board traces. choose a rectifier with a continuous current rating greater than the highest expected output current. use a rectifier with a voltage rating greater than the maximum expected input voltage, v in . use a low forward-voltage schottky rectifier for proper operation and high efficien- cy. avoid higher than necessary reverse-voltage schottky rectifiers that have higher forward-voltage drops. use a schottky rectifier with forward-voltage drop (v fb ) less than 0.45v at +25 c and maximum load current to avoid forward biasing of the internal body diode (lx to ground). internal body diode conduction may cause excessive junction temperature rise and thermal shutdown. use table 1 to choose the proper rectifier at different input voltages and output current. input bypass capacitor the discontinuous input-current waveform of the buck converter causes large ripple currents in the input capacitor. the switching frequency, peak inductor cur- rent, and the allowable peak-to-peak voltage ripple that reflects back to the source dictate the capacitance requirement. the max5035 high switching frequency allows the use of smaller-value input capacitors. the input ripple is comprised of ? v q (caused by the capacitor discharge) and ? v esr (caused by the esr of the capacitor). use low-esr aluminum electrolytic capacitors with high ripple-current capability at the input. assuming that the contribution from the esr and capaci- tor discharge is equal to 90% and 10%, respectively, cal- culate the input capacitance and the esr required for a specified ripple using the following equations: i out is the maximum output current of the converter and f sw is the oscillator switching frequency (125khz). for example, at v in = 48v, v out = 3.3v, the esr and input capacitance are calculated for the input peak-to- peak ripple of 100mv or less yielding an esr and capacitance value of 80m ? and 51f, respectively. low-esr, ceramic, multilayer chip capacitors are recom- mended for size-optimized application. for ceramic capacitors, assume the contribution from esr and capaci- tor discharge is equal to 10% and 90%, respectively. the input capacitor must handle the rms ripple current without significant rise in temperature. the maximum capacitor rms current occurs at about 50% duty cycle. esr v i i in esr out = + ? ? l l in out c i 2 ? ? ? ? ? ? = d dd vf where qsw () : 1 ? ? () , ? i vv v vf l l in out out in sw = ? d v v out in = d v v out in = l vv d if in out outmax sw = ? () . 03 v in (v) diode part number manufacturer 15mq040n ir b240a diodes, inc. b240 central semiconductor 7.5 to 36 mbrs240, mbrs1540 on semiconductor 30bq060 ir b360a diodes, inc. cmsh3-60 central semiconductor 7.5 to 56 mbrd360, mbr3060 on semiconductor 50sq100, 50sq80 ir 7.5 to 76 mbrm5100 diodes, inc. table 1. diode selection
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter 12 ______________________________________________________________________________________ ensure that the ripple specification of the input capaci- tor exceeds the worst-case capacitor rms ripple cur- rent. use the following equations to calculate the input capacitor rms current: i prms is the input switch rms current, i avgin is the input average current, and is the converter efficiency. the esr of aluminum electrolytic capacitors increases significantly at cold temperatures. use a 1f or greater value ceramic capacitor in parallel with the aluminum electrolytic input capacitor, especially for input voltages below 8v. output filter capacitor the worst-case peak-to-peak and rms capacitor ripple current, allowable peak-to-peak output ripple voltage, and the maximum deviation of the output voltage dur- ing load steps determine the capacitance and the esr requirements for the output capacitors. the output capacitance and its esr form a zero, which improves the closed-loop stability of the buck regulator. choose the output capacitor so the esr zero frequency (f z ) occurs between 20khz to 40khz. use the following equation to verify the value of f z . capacitors with 100m ? to 250m ? esr are recommended to ensure the closed- loop stability, while keeping the output ripple low. the output ripple is comprised of ? v oq (caused by the capacitor discharge) and ? v oesr (caused by the esr of the capacitor). use low-esr tantalum or aluminum electrolytic capacitors at the output. assuming that the contributions from the esr and capacitor discharge equal 80% and 20% respectively, calculate the output capacitance and the esr required for a specified rip- ple using the following equations: the max5035 has an internal soft-start time (t ss ) of 400s. it is important to keep the output rise time at startup below t ss to avoid output overshoot. the output rise time is directly proportional to the output capacitor. use 68f or lower capacitance at the output to control the overshoot below 5%. in a dynamic load application, the allowable deviation of the output voltage during the fast-transient load dic- tates the output capacitance value and the esr. the output capacitors supply the step load current until the controller responds with a greater duty cycle. the response time (t response ) depends on the closed- loop bandwidth of the converter. the resistive drop across the capacitor esr and capacitor discharge cause a voltage droop during a step load. use a com- bination of low-esr tantalum and ceramic capacitors for better transient load and ripple/noise performance. keep the maximum output-voltage deviation above the tolerable limits of the electronics being powered. assuming a 50% contribution each from the output capacitance discharge and the esr drop, use the fol- lowing equations to calculate the required esr and capacitance value: where i step is the load step and t response is the response time of the controller. controller response time is approximately one-third of the reciprocal of the closed-loop unity-gain bandwidth, 20khz typically. pcb layout considerations proper pcb layout is essential. minimize ground noise by connecting the anode of the schottky rectifier, the input bypass capacitor ground lead, and the output fil- ter capacitor ground lead to a single point (star c it v out step response oq = ? esr v i out oesr step = ? c i vf out l oq sw ? ? 22 . esr v i out oesr l = ? ? f c esr z out out = 1 2 iiiii d i v prms pk dc pk dc avgin =++ () () = 22 3 o out out in pk out l dc out l i v ii i ii i =+ =? ?? 22 , andd v v out in = iii crms prms avgin =? 2 2 2 where :
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter ______________________________________________________________________________________ 13 ground configuration). a ground plane is required. minimize lead lengths to reduce stray capacitance, trace resistance, and radiated noise. in particular, place the schottky rectifier diode right next to the device. also, place bst and vd bypass capacitors very close to the device. use the pc board copper plane connecting to v in and lx for heatsinking. max5035 gnd bst lx v in sgnd fb d1 vd l1 v out v in c in 0.1 f 0.1 f c out r1 r2 on/off figure 2. fixed output voltages v in (v) v out (v) i out (a) external components 7.5 to 76 3.3 0.5 7.5 to 76 3.3 1 c in = 68f, panasonic, eevfk2a680q c out = 68f, vishay sprague, 594d686x_010c2t c bst = 0.1f, 0805 r1 = 1m ? 1%, 0805 r2 = 384k ? 1%, 0805 d1 = 50sq100, ir l1 = 100h, coilcraft inc., do5022p-104 7.5 to 76 5 0.5 7.5 to 76 5 1 c in = 68f, panasonic, eevfk2a680q c out = 68f, vishay sprague, 594d68x_010c2t c bst = 0.1f, 0805 r1 = 1m ? 1%, 0805 r2 = 384k ? 1%, 0805 d1 = 50sq100, ir l1 = 100h, coilcraft inc., do5022p-104 15 to 76 12 1 c in = 68f, panasonic, eevfk2a680q c out = 15f, vishay sprague, 594d156x0025c2t c bst = 0.1f, 0805 r1 = 1m ? 1%, 0805 r2 = 139k ? 1%, 0805 d1 = 50sq100, ir l1 = 220h, coilcraft inc., do5022p-224 table 2. typical external components selection (circuit of figure 2) application circuits
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter 14 ______________________________________________________________________________________ v in (v) v out (v) i out (a) external components 3.3 1 c in = 220f, panasonic, eevfk1e221p c out = 68f, vishay sprague, 594d686x_010c2t c bst = 0.1f, 0805 r1 = 1m ? 1%, 0805 r2 = 274k ? 1%, 0805 d1 = b220, diodes inc. l1 = 100h, coilcraft inc., do5022p-104 9 to 14 51 c in = 220f, panasonic, eevfk1e221p c out = 68f, vishay sprague, 594d686x_010c2t c bst = 0.1f, 0805 r1 = 1m ? 1%, 0805 r2 = 274k ? 1%, 0805 d1 = b220, diodes inc. l1 = 100h, coilcraft inc., do5022p-104 3.3 1 c in = 220f, panasonic, eevfk1h221p c out = 68f, vishay sprague, 594d686x_010c2t c bst = 0.1f, 0805 r1 = 1m ? 1%, 0805 r2 = 130k ? 1%, 0805 d1 = mbrs2040, on semiconductor l1 = 100h, coilcraft inc., do5022p-104 51 c in = 220f, panasonic, eevfk1h221p c out = 68f, vishay sprague, 594d686x_010c2t c bst = 0.1f, 0805 r1 = 1m ? 1%, 0805 r2 = 130k ? 1%, 0805 d1 = mbrs2040, on semiconductor l1 = 100h, coilcraft inc., do5022p-104 18 to 36 12 1 c in = 220f, panasonic, eevfk1h221p c out = 15f, vishay sprague, 594d156x_0025c2t c bst = 0.1f, 0805 r1 = 1m ? 1%, 0805 r2 = 130k ? 1%, 0805 d1 = mbrs2040, on semiconductor l1 = 220h, coilcraft inc., do5022p-224 table 2. typical external components selection (circuit of figure 2) (continued)
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter ______________________________________________________________________________________ 15 supplier phone fax website avx corporation 843-946-0238 843-626-3123 www.avxcorp.com coilcraft, inc. 847-639-6400 847-639-1469 www.coilcraft.com diodes incorporated 805-446-4800 805-446-4850 www.diodes.com panasonic corp. 800-344-2112 714-737-7323 www.panasonic.com sanyo electric co., ltd. 619-661-6835 619-661-1055 www.sanyo.com tdk corp. 847-803-6100 847-390-4405 www.component.tdk.com vishay 402-563-6866 402-563-6296 www.vishay.com table 3. component suppliers max5035 c in 68 f c out 68 f l1 100 h fb v out 5v at 1a bst lx sgnd 0.1 f 0.1 f gnd v in 12v v in ptc* rt ct d1 b240 vd *locate ptc as close to heat-dissipating components as possible. on/off figure 3. load temperature monitoring with on/ off (requires accurate v in )
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter 16 ______________________________________________________________________________________ max5035b c in 68 f c out 68 f l1 220 h fb v out 5v bst lx sgnd 0.1 f 0.1 f gnd v in 7.5v to 36v v in r1 rt ct d1 b240 vd on/off max5035a c' in 68 f c' out 68 f l1' 100 h fb v' out 3.3v bst lx sgnd 0.1 f 0.1 f gnd v in r1' rt' ct' d1' b240 vd on/off figure 4. dual-sequenced dc-dc converters (startup delay determined by r1/r1, ct/ct and rt/rt) chip information process: bicmos ordering information (continued) part temp range pin- package ou tpu t vo lta ge ( v) max5035cusa 0c to +85c 8 so max5035cupa 0c to +85c 8 pdip max5035casa -40c to +125c 8 so m ax 5035c as a/v + -40c to +125c 8 so 12 max5035dusa 0c to +85c 8 so max5035dupa 0c to +85c 8 pdip max5035dasa -40c to +125c 8 so m ax 5035d as a/v + -40c to +125c 8 so adj max5035eusa 0c to +85c 8 so max5035easa -40c to +125c 8 so m ax 5035e as a/v + -40c to +125c 8 so adj /v denotes an automotive qualified part. + denotes a lead(pb)-free/rohs-compliant package. package information for the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages . note that a +, #, or - in the package code indicates rohs status only. package drawings may show a different suffix character, but the drawing pertains to the package regardless of rohs status. package type package code outline no. land pattern no. 8 so s8+2 21-0041 90-0096 8 pdip p8+1 21-0043
max5035 1a, 76v, high-efficiency maxpower step-down dc-dc converter maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 17 ? 2011 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision number revision date description pages changed 0 9/03 initial release 1 6/04 removed future-product asterisks and made specification changes 1, 2, 3 2 1/07 modified absolute maximum ratings section, updated ordering information , style edits 2, 3 3 5/09 modified absolute maximum ratings section 1, 2, 16, 18 4 4/10 updated electrical characteristics table specifications 2, 3, 4, 16, 17 5 5/11 added new variant (max5035e) 1C4, 9, 10, 16 revision history

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