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general description the max15004a/b/max15005a/b high-performance, current-mode pwm controllers operate at an automotive input voltage range from 4.5v to 40v (load dump). the input voltage can go lower than 4.5v after startup if in is bootstrapped to a boosted output voltage. the controllers integrate all the building blocks necessary for implementing fixed-frequency isolated/nonisolated power supplies. the general-purpose boost, flyback, forward, and sepic con - verters can be designed with ease around the max15004/ max15005. the current-mode control architecture offers excellent line- transient response and cycle-by-cycle current limit while simplifying the frequency compensation. programmable slope compensation simplifies the design further. a fast 60ns current-limit response time, low 300mv current-limit threshold makes the controllers suitable for high-efficiency, high-frequency dc-dc converters. the devices include an internal error amplifier and 1% accurate reference to facilitate the primary-side regulated, single-ended flyback converter or nonisolated converters. an external resistor and capacitor network programs the switching frequency from 15khz to 500khz (1mhz for the max15005a/b). the max15004a/b/max15005a/b provide a sync input for synchronization to an external clock. the maximum fet-driver duty cycle for the max15004a/b is 50%. the maximum duty cycle can be set on the max15005a/b by selecting the right combina - tion of rt and ct. the input undervoltage lockout (on/ off ) programs the input-supply startup voltage and can be used to shutdown the converter to reduce the total shutdown current down to 10a. protection features include cycle-by-cycle and hiccup current limit, output over-voltage protection, and thermal shutdown. the max15004a/b/max15005a/b are available in space- saving 16-pin tssop and thermally enhanced 16-pin tssop-ep packages. all devices operate over the -40c to +125c automotive temperature range. applications automotive vacuum fluorescent display (vfd) power supply isolated flyback, forward, nonisolated sepic, boost converters beneits and features wide supply voltage range meets automotive power-supply operating requirement including cold crank conditions ? 4.5v to 40v operating input voltage range (can operate at lower voltage after startup if input is bootstrapped to a boosted output) control architecture offers excellent performance while simplifying the design ? current-mode control ? 300mv, 5% accurate current-limit threshold voltage ? programmable slope compensation ? 50% (max15004) or adjustable (max15005) maximum duty cycle accurate, adjustable switching frequency and synchronization avoids interference with sensitive radio bands ? switching frequency adjustable from 15khz to 500khz (1mhz for the max15005a/b) ? rc programmable 4% accurate switching frequency ? external frequency synchronization built-in protection capability for improved system reliability ? cycle-by-cycle and hiccup current-limit protection ? overvoltage and thermal-shutdown protection ? -40c to +125c automotive temperature range ? aec-q100 qualified 19-0723; rev 6; 12/15 pin configuration appears at end of data sheet. note: all devices are specified over the -40c to +125c temperature range. + denotes a lead(pb)-free/rohs-compliant package. /v denotes an automotive qualified part. * ep = exposed pad. part pin-package max duty cycle max15004 aaue+ 16 tssop-ep* 50% MAX15004AAUE/v+ 16 tssop-ep* 50% max15004baue+ 16 tssop 50% max15004baue/v+ 16 tssop 50% max15005 aaue+ 16 tssop-ep* programmable max15005aaue/v+ 16 tssop-ep* programmable max15005baue+ 16 tssop programmable max15005baue/v+ 16 tssop programmable max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers ordering information evaluation kit available downloaded from: http:///
in to sgnd ........................................................... -0.3v to +45v in to pgnd ........................................................... -0.3v to +45v on/ off to sgnd ...................................... -0.3v to (v in + 0.3v) ovi, slope, rtct, sync, ss, fb, comp, cs to sgnd ..................................... -0.3v to (v reg5 + 0.3v) v cc to pgnd ........................................................ -0.3v to +12v reg5 to sgnd ....................................................... -0.3v to +6v out to pgnd .......................................... -0.3v to (v cc + 0.3v) sgnd to pgnd .................................................... -0.3v to +0.3v v cc sink current (clamped mode) .................................... 35ma out current (< 10s transient) ......................................... 1.5a continuous power dissipation* (t a = +70c) 16-pin tssop-ep (derate 21.3mw/c above +70c) ............................................................ 1702mw 16-pin tssop (derate 9.4mw/c above +70c) ............ 754mw operating junction temperature range .......... -40c to +125c junction temperature ...................................................... +150c storage temperature range ............................ -60c to +150c lead temperature (soldering, 10s) ................................. +300c soldering temperature (reflow) ....................................... +260c (v in = 14v, c in = 0.1f, c vcc = 0.1f // 1f, c reg5 = 1f, v on/ off = 5v, c ss = 0.01f, c slope = 100pf, rt = 13.7k, ct = 560pf, v sync = v ovi = v fb = v cs = 0v, comp = unconnected, out = unconnected. t a = t j = -40c to +125c, unless otherwise noted. typical values are at t a = +25c. all voltages are referenced to pgnd, unless otherwise noted.) (note 1) (figure 5) * as per jedec51 standard, multilayer board. parameter symbol conditions min typ max units power supply input supply range v in 4.5 40.0 v operating supply current i q v in = 40v, f osc = 150khz 2 3.1 ma on/ off control input-voltage threshold v on v on/ off rising 1.05 1.23 1.40 v input-voltage hysteresis v hyst-on 75 mv input bias current i b-on/ off v on/ off = 40v 0.5 a shutdown current i shdn v on/ off = 0v 10 20 a internal 7.4v ldo (v cc ) output (v cc ) voltage set point v vcc i vcc = 0 to 20ma (sourcing) 7.15 7.4 7.60 v line regulation v in = 8v to 40v 1 mv/v uvlo threshold voltage v uvlo-vcc v cc rising 3.15 3.5 3.75 v uvlo hysteresis v hyst-uvlo 500 mv dropout voltage v in = 4.5v, i vcc = 20ma (sourcing) 0.25 0.5 v output current limit i vcc-ilim i vcc sourcing 45 ma internal clamp voltage v vcc-clamp i vcc = 30ma (sinking) 10.0 10.4 10.8 v internal 5v ldo (reg5) output (reg5) voltage set point v reg5 v cc = 7.5v, i reg5 = 0 to 15ma (sourcing) 4.75 4.95 5.05 v line regulation v cc = 5.5v to 10v 2 mv/v dropout voltage v cc = 4.5v, i reg5 = 15ma (sourcing) 0.25 0.5 v output current limit i reg5-ilim i reg5 sourcing 32 ma max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 2 absolute maximum ratings stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. electrical characteristics downloaded from: http:///
(v in = 14v, c in = 0.1f, c vcc = 0.1f // 1f, c reg5 = 1f, v on/ off = 5v, c ss = 0.01f, c slope = 100pf, rt = 13.7k, ct = 560pf, v sync = v ovi = v fb = v cs = 0v, comp = unconnected, out = unconnected. t a = t j = -40c to +125c, unless otherwise noted. typical values are at t a = +25c. all voltages are referenced to pgnd, unless otherwise noted.) (note 1) (figure 5) parameter symbol conditions min typ max units oscillator (rtct) oscillator frequency range f osc f osc = 2 x f out for max15004a/b, f osc = f out for max15005a/b 15 1000 khz rtct peak trip level v th,rtct 0.55 x v reg5 v rtct valley trip level v tl,rtct 0.1 x v reg5 v rtct discharge current i dis,rtct v rtct = 2v 1.30 1.33 1.36 ma oscillator frequency accuracy (note 2) rt = 13.7k?, ct = 4.7nf, f osc (typ) = 18khz -4 +4 % rt = 13.7k?, ct = 560pf, f osc (typ) = 150khz -4 +4 rt = 21k?, ct = 100pf, f osc (typ) = 500khz -5 +5 rt = 7k?, ct = 100pf, f osc (typ) = 1mhz -7 +7 maximum pwm duty cycle(note 3) d max max15004a/b 50 % max15005a/b, rt = 13.7k?, ct = 560pf, f osc (typ) = 150khz 78.5 80 81.5 minimum on-time t on-min v in = 14v 110 170 ns sync lock-in frequency range (note 4) rt = 13.7k?, ct = 560pf, f osc (typ) = 150khz 102 200 %f osc sync high-level voltage v ih-sync 2 v sync low-level voltage v il-sync 0.8 v sync input current i sync v sync = 0 to 5v -0.5 +0.5 a sync minimum input pulse width 50 ns error amplifier/soft-start soft-start charging current i ss v ss = 0v 8 15 21 a ss reference voltage v ss 1.215 1.228 1.240 v ss threshold for hiccup enable v ss rising 1.1 v fb regulation voltage v ref-fb comp = fb, i comp = -500a to +500a 1.215 1.228 1.240 v fb input offset voltage v os-fb comp = 0.25v to 4.5v, i comp = -500a to +500a, v ss = 0 to 1.5v -5 +5 mv fb input current v fb = 0 to 1.5v -300 +300 na comp sink current i comp-sink v fb = 1.5v, v comp = 0.25v 3 5.5 ma max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 3 electrical characteristics (continued) downloaded from: http:///
(v in = 14v, c in = 0.1f, c vcc = 0.1f // 1f, c reg5 = 1f, v on/ off = 5v, c ss = 0.01f, c slope = 100pf, rt = 13.7k, ct = 560pf, v sync = v ovi = v fb = v cs = 0v, comp = unconnected, out = unconnected. t a = t j = -40c to +125c, unless otherwise noted. typical values are at t a = +25c. all voltages are referenced to pgnd, unless otherwise noted.) (note 1) (figure 5) parameter symbol conditions min typ max units comp source current i comp- source v fb = 1v, v comp = 4.5v 1.3 2.8 ma comp high voltage v oh-comp v fb = 1v, i comp = 1ma (sourcing) v reg5 - 0.5 v reg5 - 0.2 v comp low voltage v ol-comp v fb = 1.5v, i comp = 1ma (sinking) 0.1 0.25 v open-loop gain a eamp 100 db unity-gain bandwidth ugf eamp 1.6 mhz phase margin pm eamp 75 degrees comp positive slew rate sr+ 0.5 v/s comp negative slew rate sr- -0.5 v/s pwm comparator current-sense gain a cs-pwm v comp /v cs (note 5) 2.85 3 3.15 v/v pwm propagation delay to out t pd-pwm cs = 0.15v, from v comp falling edge: 3v to 0.5v to out falling (excluding leading-edge blanking time) 60 ns pwm comparator current-sense leading-edge blanking time t cs-blank 50 ns current-limit comparator current-limit threshold voltage v ilim 290 305 317 mv current-limit input bias current i b-cs out= high, 0 v cs 0.3v -2 +2 a ilimit propagation delay to out t pd-ilim from cs rising above v ilim (50mv overdrive) to out falling (excluding leading-edge blanking time) 60 ns ilim comparator current-sense leading-edge blanking time t cs-blank 50 ns number of consecutive ilimit events to hiccup 7 hiccup timeout 512 clock periods slope compensation (note 6) slope capacitor charging current i slope v slope = 100mv 9.8 10.5 11.2 a slope compensation c slope = 100pf 25 mv/s slope compensation tolerance (note 2) c slope = 100pf -4 +4 % slope compensation range c slope = 22pf 110 mv/s c slope = 1000pf 2.5 max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 4 electrical characteristics (continued) downloaded from: http:///
(v in = 14v, c in = 0.1f, c vcc = 0.1f // 1f, c reg5 = 1f, v on/ off = 5v, c ss = 0.01f, c slope = 100pf, rt = 13.7k, ct = 560pf, v sync = v ovi = v fb = v cs = 0v, comp = unconnected, out = unconnected. t a = t j = -40c to +125c, unless otherwise noted. typical values are at t a = +25c. all voltages are referenced to pgnd, unless otherwise noted.) (note 1) (figure 5) note 1: 100% production tested at +125c. limits over the temperature range are guaranteed by design. note 2: guaranteed by design; not production tested. note 3: for the max15005a/b, d max depends upon the value of rt. see figure 3 and the oscillator frequency/external synchronization section. note 4: the external sync pulse triggers the discharge of the oscillator ramp. see figure 2. during external sync, d max = 50% for the max15004a/b; for the max15005a/b, there is a shift in d max with f sync /f osc ratio (see the oscillator frequency/ external synchronization section). note 5: the parameter is measured at the trip point of latch, with 0 v cs 0.3v, and fb = comp. note 6: slope compensation = (2.5 x 10 -9 )/c slope mv/s. see the applications information section. parameter symbol conditions min typ max units output driverdriver output impedance r out-n v cc = 8v (applied externally), i out = 100ma (sinking) 1.7 3.5 ? r out-p v cc = 8v (applied externally), i out = 100ma (sourcing) 3 5 driver peak output current i out-peak c out = 10nf, sinking 1000 ma c out = 10nf, sourcing 750 overvoltage comparator overvoltage comparator input threshold v ov-th v ovi rising 1.20 1.228 1.26 v overvoltage comparator hysteresis v ov-hyst 125 mv overvoltage comparator delay td ovi from ovi rising above 1.228v to out falling, with 50mv overdrive 1.6 s ovi input current i ovi v ovi = 0 to 5v -0.5 +0.5 a thermal shutdown shutdown temperature t shdn temperature rising 160 c thermal hysteresis t hyst 15 c max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 5 electrical characteristics (continued) downloaded from: http:///
v in = 14v, c in = 0.1f, c vcc = 0.1f // 1f, c reg5 = 1f, v on/ off = 5v, c ss = 0.01f, c slope = 100pf, rt = 13.7k, ct = 560pf. t a = +25c, unless otherwise noted.) v in supply current (i supply ) vs. oscillator frequency (f osc ) frequency (khz) v in supply current (ma) max15004 toc02 10 60 110 160 210 260 310 360 410 460 510 1 4 7 10 13 16 19 22 25 28 31 max15005v in = 14v ct = 220pf c out = 10nf c out = 0nf shutdown supply current vs. supply voltage supply voltage (v) v in shutdown supply current (a) max15004 toc03 5 10 15 20 25 30 35 40 45 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 t a = +135c t a = -40c t a = +25c v cc output voltage vs. v in supply voltage v in supply voltage (v) v cc output voltage (v) max15004 toc04 5 10 15 20 25 30 35 40 45 5.0 5.5 6.0 6.5 7.0 7.5 i vcc = 0ma i vcc = 1ma i vcc = 20ma reg5 output voltage vs. v cc voltage v cc voltage (v) reg5 output voltage (v) max15004 toc06 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 4.700 4.725 4.750 4.775 4.800 4.825 4.850 4.875 4.900 4.925 4.950 4.975 5.000 i reg5 = 1ma (sourcing) i reg5 = 15ma (sourcing) reg5 dropout voltage vs. i reg5 i reg5 (ma) reg5 ldo dropout voltage (v) max15004 toc07 0 2 4 6 8 10 12 14 0 0.03 0.05 0.08 0.10 0.13 0.15 0.18 0.20 0.23 0.25 0.28 0.30 t a = +135c t a = +25c t a = -40c t a = +125c v cc = 4.5 v in = v on/ off v in uvlo hysteresis vs. temperature temperature (c) v in uvlo hysteresis (mv) max15004 toc01 -40 -15 10 35 60 85 110 135 0 10 20 30 40 50 60 70 80 90 100 110 120 oscillator frequency (f osc ) vs. v in supply voltage v in supply voltage (v) oscillator frequency (khz) max15004 toc08 5.5 10.5 15.5 20.5 25.5 30.5 35.5 40.5 45.5 140 141 142 143 144 145 146 147 148 149 150 t a = +125c t a = -40c t a = +25c t a = +135c rt = 13.7k ? ct = 560pf max15005 oscillator frequency (f osc ) vs. rt/ct rt (k ? ) oscillator frequency (khz) max15004 toc09 1 10 100 1000 10 100 1000 ct = 220pf ct = 1500pf ct = 1000pf ct = 560pf ct = 2200pf ct = 3300pf ct = 100pf max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers maxim integrated 6 www.maximintegrated.com typical operating characteristics downloaded from: http:///
v in = 14v, c in = 0.1f, c vcc = 0.1f // 1f, c reg5 = 1f, v on/ off = 5v, c ss = 0.01f, c slope = 100pf, rt = 13.7k, ct = 560pf. t a = +25c, unless otherwise noted.) max15005 maximum duty cycle vs. output frequency (f out ) output frequency (khz) maximum duty cycle (%) max15004 toc10 50 55 60 65 70 75 80 85 90 95 100 10 100 1000 ct = 220pf ct = 1500pf ct = 1000pf ct = 560pf ct = 2200pf ct = 3300pf ct = 100pf max15004 maximum duty cycle vs. temperature temperature (c) maximum duty cycle (%) max15004 toc11 -40 -15 10 35 60 85 110 135 45 46 47 48 49 50 51 52 53 54 55 f out = 75khz max15005 maximum duty cycle vs. temperature temperature (c) maximum duty cycle (%) max15004 toc12 -40 -15 10 35 60 85 110 135 65 67 69 71 73 75 77 79 81 83 85 ct = 560pfrt = 13.7k ? f osc = f out = 150khz maximum duty cycle vs. f sync /f osc ratio f sync /f osc ratio maximum duty cycle (%) max15004 toc13 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 50 55 60 65 70 75 80 c rtct = 220pf r rtct = 10k ? f osc = f out = 418khz ct = 560pfrt = 10k ? f osc = f out = 180khz max15005 error amplifier open-loop gain and phase vs. frequency frequency (hz) gain (db) max15004 toc14 phase (degrees) 60 100 140 180 220 260 300 340 -10 0 10 20 30 40 50 60 70 80 90 100 110 0.1 1 10 100 1k 10k 100k 1m 10m gain phase cs-to-out delay vs. temperature temperature (c) cs-to-out delay (ns) max15004 toc15 10 0 20 30 40 50 60 70 80 90 100 -40 -15 10 35 60 85 110 135 v cs overdrive = 190mv v cs overdrive = 50mv ovi to out delay through overvoltage comparator max15004 toc16 1s/div v out 2v/div v ovi 500mv/div v out v ovi driver output peak source and sink current max15004 toc17 400ns/div v out 5v/div i out 1a/div c out = 10nf power-up sequence through v in max15004 toc18 2ms/div v in 10v/div v cc 5v/div reg55v/div v out 5v/div v on/ off = 5v max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers maxim integrated 7 www.maximintegrated.com typical operating characteristics (continued) downloaded from: http:///
v in = 14v, c in = 0.1f, c vcc = 0.1f // 1f, c reg5 = 1f, v on/ off = 5v, c ss = 0.01f, c slope = 100pf, rt = 13.7k, ct = 560pf. t a = +25c, unless otherwise noted.) power-down sequence through v in max15004 toc19 4ms/div v in 10v/div v cc 5v/div reg55v/div v out 5v/div v on/ off = 5v power-up sequence through on/ off max15004 toc20 1ms/div on/ off 5v/div v cc 5v/divreg5 5v/div v out 5v/div power-down sequence through on/ off max15004 toc21 400ms/div on/ off 5v/div v cc 5v/divreg5 5v/div v out 5v/div line transient for v in step from 14v to 5.5v max15004 toc22 100s/div v in 10v/div v cc 5v/divreg5 5v/div v out 5v/div line transient for v in step from 14v to 40v max15004 toc23 100s/div v in 20v/div v cc 5v/div reg55v/div v out 5v/div hiccup mode for flyback circuit (figure 7) max15004 toc24 10s/div v cs 200mv/div v anode 1v/divi short 500ma/div drain waveform in flyback converter (figure 7) max15004 toc25 4s/div 10v/div i load = 10ma max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers maxim integrated 8 www.maximintegrated.com typical operating characteristics (continued) downloaded from: http:///
pin name function 1 in input power supply. bypass in with a minimum 0.1f ceramic capacitor to pgnd. 2 on/ off on/ off input. connect on/ off to in for always-on operation. to externally program the uvlo threshold of the in supply, connect a resistive divider between in, on/ off , and sgnd. pull on/ off to sgnd to disable the controller. 3 ovi overvoltage comparator input. connect a resistive divider between the output of the power supply, ovi, and sgnd to set the output overvoltage threshold. 4 slope programmable slope compensation capacitor input. connect a capacitor (c slope ) to sgnd to set the amount of slope compensation.slope compensation = (2.5 x 10 -9 )/c slope mv/s with c slope in farads. 5 n.c. no connection. not internally connected. 6 rtct oscillator-timing network input. connect a resistor from rtct to reg5 and a capacitor from rtct to sgnd to set the oscillator frequency (see the oscillator frequency/external synchronization section). 7 sgnd signal ground. connect sgnd to sgnd plane. 8 sync external-clock synchronization input. connect sync to sgnd when not using an external clock. 9 ss soft-start capacitor input. connect a capacitor from ss to sgnd to set the soft-start time interval. 10 fb internal error-ampliier inverting input. the noninverting input is internally connected to ss. 11 comp error-ampliier output. connect the frequency compensation network between fb and comp. 12 cs current-sense input. the current-sense signal is compared to a signal proportional to the error-ampl iier output voltage. 13 reg5 5v low-dropout regulator output. bypass reg5 with a 1f ceramic capacitor to sgnd. 14 pgnd power ground. connect pgnd to the power ground plane. 15 out gate driver output. connect out to the gate of the external n-channel mosfet. 16 v cc 7.4v low-dropout regulator outputdriver power source. bypass v cc with 0.1f and 1f or higher ceramic capacitors to pgnd. do not connect external supply or bootstrap to v cc . ep exposed pad (max15004a/max15005a only). connect ep to the sgnd plane to improve thermal performance. do not use the ep as an electrical connection. max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 9 pin description downloaded from: http:///
max15004a/bmax15005a/b preregulator reference slope compensation eamp ref-amp thermal shutdown ov-comp on/ off comp oscillator 7 consecutive events counter 7.4v ldo reg 5v ldo reg uvb v cc uvb 3.5v uvlo 50ns lead delay driver r 0.3v 2r ss_ok reset 1.228v 1.228v 1.228v 1 23 46 7 8 sync sgnd rtct slope ovi on/ off in v cc 16 out 15 pgnd 14 reg5 13 cs 12 comp 11 fb 10 ss 9 off off set reset ovrld clk ovrld pwm- comp ilimit comp max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 10 functional diagram downloaded from: http:///
detailed description the max15004a/b/max15005a/b are high-performance, current-mode pwm controllers for wide input-voltage range isolated/nonisolated power supplies. these con - trollers are for use as general-purpose boost, flyback, and sepic controllers. the input voltage range of 4.5v to 40v makes it ideal in automotive applications such as vacuum fluorescent display (vfd) power supplies. the internal low-dropout regulator (v cc regulator) enables the max15004a/b/max15005a/b to operate directly from an automotive battery input. the input voltage can go lower than 4.5v after startup if in is bootstrapped to a boosted output voltage. the undervoltage lockout (on/ off ) allows the devices to program the input-supply startup voltage and ensures predictable operation during brownout conditions. the devices contain two internal regulators, v cc and reg5. the v cc regulator output voltage is set at 7.4v and reg5 regulator output voltage at 5v 2%. the input undervoltage lockout (uvlo) circuit monitors the v cc voltage and turns off the converter when the v cc voltage drops below 3.5v (typ). an external resistor and capacitor network programs the switching frequency from 15khz to 500khz. the max15004a/b/max15005a/b provide a sync input for synchronization to an external clock. the out (fet- driver output) duty cycle for the max15004a/b is 50%. the maximum duty cycle can be set on max15005a/b by selecting the right combination of rt and ct. the rtct discharge current is trimmed to 2%, allowing accurate setting of the duty cycle for the max15005. an internal slope-compensation circuit stabilizes the current loop when operating at higher duty cycles and can be pro - grammed externally. the max15004/max15005 include an internal error amplifier with 1% accurate reference to regulate the output in nonisolated topologies using a resistive divider. the internal reference connected to the noninverting input of the error amplifier can be increased in a controlled manner to obtain soft-start. a capacitor connected at ss to ground programs soft-start to reduce inrush current and prevent output overshoot. the max15004/max15005 include protection features like hiccup current limit, output overvoltage, and ther - mal shutdown. the hiccup current-limit circuit reduces the power delivered to the electronics powered by the max15004/max15005 converter during severe fault con - ditions. the overvoltage circuit senses the output using the path different from the feedback path to provide meaningful overvoltage protection. during continuous high input operation, the power dissipation into the max15004/max15005 could exceed its limit. internal thermal shutdown protection safely turns off the converter when the junction heats up to 160c. current-mode control loop the advantages of current-mode control overvoltage- mode control are twofold. first, there is the feed-forward characteristic brought on by the controllers ability to adjust for variations in the input voltage on a cycle-by-cycle basis. secondly, the stability requirements of the current- mode controller are reduced to that of a single-pole system unlike the double pole in voltage-mode control. the max15004/max15005 offer peak current-mode control operation to make the power supply easy to design with. the inherent feed-forward characteristic is useful especially in an automotive application where the input voltage changes fast during cold-crank and load dump con - ditions. while the current-mode architecture offers many advantages, there are some shortcomings. for higher duty- cycle and continuous conduction mode operation where the transformer does not discharge during the off duty cycle, subharmonic oscillations appear. the max15004/ max15005 offer programmable slope compensation using a single capacitor. another issue is noise due to turn-on of the primary switch that may cause the premature end of the on cycle. the current-limit and pwm comparator inputs have leading-edge blanking. all the shortcomings of the current-mode control are addressed in the max15004/ max15005, making it ideal to design for automotive power conversion applications. internal regulators v cc and reg5 the internal ldo converts the automotive battery voltage input to a 7.4v output voltage (v cc ). the v cc output is set at 7.4v and operates in a dropout mode at input volt - ages below 7.5v. the internal ldo is capable of deliver - ing 20ma current, enough to provide power to internal control circuitry and the gate drive. the regulated v cc keeps the driver output voltage well below the absolute maximum gate voltage rating of the mosfet especially during the double battery and load dump conditions. max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 11 downloaded from: http:///
the second 5v ldo regulator from v cc to reg5 pro - vides power to the internal control circuits. this ldo can also be used to source 15ma of external load current. bypass v cc and reg5 with a parallel combination of 1f and 0.1f low-esr ceramic capacitors. additional capacitors (up to 22f) at v cc can be used although they are not necessary for proper operation of the max15004/ max15005. startup operation/uvlo/on/ off the max15004a/b/max15005a/b feature two undervolt - age lockouts (uvlo). the internal uvlo monitors the v cc -regulator and turns on the converter once v cc rises above 3.5v. the internal uvlo circuit has about 0.5v hysteresis to avoid chattering during turn-on. an external undervoltage lockout can be achieved by controlling the voltage at the on/ off input. the on/ off input threshold is set at 1.23v (rising) with 75mv hysteresis. before any operation can commence, the on/ off volt - age must exceed the 1.23v threshold. calculate r1 in figure 1 by using the following formula: on uvlo v r1 1 r2 v ?? = ? ?? ?? where v uvlo is the on/ off s 1.23v rising threshold, and v on is the desired input startup voltage. choose an r2 value in the 100k range. the uvlo circuits keep the pwm comparator, ilim comparator, oscillator, and output driver shut down to reduce current consumption (see the functional diagram ). the on/ off input can be used to disable the max15004/max15005 and reduce the standby current to less than 20a. soft-start the max15004/max15005 are provided with an externally adjustable soft-start function, saving a number of external components. the ss is a 1.228v reference bypass connection for the max15004a/b/max15005a/b and also controls the soft-start period. at startup, after v in is applied and the uvlo thresholds are reached, the device enters soft-start. during soft-start, 15a is sourced into the capacitor (c ss ) connected from ss to gnd causing the reference voltage to ramp up slowly. the hiccup mode of operation is disabled during soft-start. when v ss reaches 1.228v, the output as well as the hiccup mode become fully active. set the soft-start time (t ss ) using following equation: ( ) ss ss 6 1.23(v) c t 15 10 a ? = where t ss is in seconds and c ss is in farads. the soft-start programmability is important to control the input inrush current issue and also to avoid the max15004/max15005 power supply from going into the unintentional hiccup during the startup. the required soft- start time depends on the topology used, current-limit setting, output capacitance, and the load condition.oscillator frequency/external synchronization use an external resistor and capacitor at rtct to pro - gram the max15004a/b/max15005a/b internal oscilla - tor frequency from 15khz to 1mhz. the max15004a/b output switching frequency is one-half the programmed oscillator frequency with a 50% maximum duty-cycle limit. the max15005a/b output switching frequency is the same as the oscillator frequency. the rc network connected to rtct controls both the oscillator frequen - cy and the maximum duty cycle. the ct capacitor charges and discharges from (0.1 x v reg5 ) to (0.55 x v reg5 ). it charges through rt and discharges through an internal trimmed controlled current sink. the maximum duty cycle is inversely proportional to the discharge time (t discharge ). see figures 3a and 3b for a coarse selection of capacitor values for a given switching frequen - cy and maximum duty cycle and then use the following figure 1. setting the max15004a/b/max15005a/b undervoltage-lockout threshold max15004a/bmax15005a/b on/ off r1 1.23v r2 v in max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 12 downloaded from: http:///
equations to calculate the resistor value to fine-tune the switching frequency and verify the worst-case maximum duty cycle. max charge osc charge discharge 3 osc charge discharge osc charge discharge d t f t rt 0.7 ct 2.25(v) rt ct t (1.33 10 (a) rt) 3.375(v) 1 ...................use this equation if f 500 khz tt f 1 .......usethis equation t t 160ns ? ? = = = + = ++ osc if f 500khz ?? ? ? ? > ?? where f osc is the oscillator frequency, rt is a resistor connected from rtct to reg5, and ct is a capacitor connected from rtct to sgnd. verify that the oscilla - tor frequency value meets the target. above calculations could be repeated to fine-tune the switching frequency. the max15004a/b is a 50% maximum duty-cycle part, while the max15005a/b is 100% maximum duty-cycle part. out osc 1 ff 2 = for the max15004a/b and out osc ff = for the max15005a/b. the max15004a/b/max15005a/b can be synchronized using an external clock at the sync input. for proper frequency synchronization, syncs input frequency must be at least 102% of the programmed internal oscillator frequency. connect sync to sgnd when not using an external clock. a rising clock edge on sync is interpreted as a synchronization input. if the sync signal is lost, the internal oscillator takes control of the switching rate, returning the switching frequency to that set by rc net - work connected to rtct. this maintains output regulation even with intermittent sync signals. n-channel mosfet driver figure 2. timing diagram for internal oscillator vs. external sync and d max behavior rtct clkint sync out rtct clkint sync out d = 50% d = 50% d = 81.25% d = 80% with sync input max15004a/b (d max = 50%) max15005a/b (d max = 81%) without sync input with sync input without sync input max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 13 downloaded from: http:///
out drives the gate of an external n-channel mosfet. the driver is powered by the internal regulator (v cc ), internally set to approximately 7.4v. the regulated v cc voltage keeps the out voltage below the maximum gate voltage rating of the external mosfet. out can source 750ma and sink 1000ma peak current. the average current sourced by out depends on the switching frequency and total gate charge of the external mosfet. error ampliier the max15004a/b/max15005a/b include an internal error amplifier. the noninverting input of the error ampli - fier is connected to the internal 1.228v reference and feedback is provided at the inverting input. high 100db open-loop gain and 1.6mhz unity-gain bandwidth allow good closed-loop bandwidth and transient response. moreover, the source and sink current capability of 2ma provides fast error correction during the output load tran - sient. for figure 5, calculate the power-supply output voltage using the following equation: a out ref b r v 1v r ?? = + ?? ?? where v ref = 1.228v. the amplifiers noninverting input is internally connected to a soft-start circuit that gradu - ally increases the reference voltage during startup. this forces the output voltage to come up in an orderly and well-defined manner under all load conditions. slope compensation the max15004a/b/max15005a/b use an internal ramp generator for slope compensation. the internal ramp signal resets at the beginning of each cycle and slews at the rate programmed by the external capacitor connected to slope. the amount of slope compensation needed depends on the downslope of the current waveform. adjust the max15004a/b/max15005a/b slew rate up to 110mv/s using the following equation: 9 slope 2.5 10 (a) slope compensation (mv s) c ? = where c slope is the external capacitor at slope in farads.current limit the current-sense resistor (r cs ), connected between the source of the mosfet and ground, sets the current limit. the cs input has a voltage trip level (v cs ) of 305mv. the current-sense threshold has 5% accuracy. set the current- limit threshold 20% higher than the peak switch current at the rated output power and minimum input voltage. use the following equation to calculate the value of r s : ( ) s cs pk r v i 1.2 = where i pri is the peak current that flows through the mosfet at full load and minimum v in . figure 3a. max15005 maximum duty cycle vs. output frequency. figure 3b. oscillator frequency vs. rt/ct max15005 maximum duty cycle vs. output frequency (f out ) output frequency (khz) maximum duty cycle (%) 50 55 60 65 70 75 80 85 90 95 100 10 100 1000 ct = 220pf ct = 1500pf ct = 1000pf ct = 560pf ct = 2200pf ct = 3300pf ct = 100pf oscillator frequency (f osc ) vs. rt/ct rt (k ? ) oscillator frequency (khz) 1 10 100 1000 10 100 1000 ct = 220pf ct = 1500pf ct = 1000pf ct = 560pf ct = 2200pf ct = 3300pf ct = 100pf max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 14 downloaded from: http:///
when the voltage produced by this current (through the current-sense resistor) exceeds the current-limit com - parator threshold, the mosfet driver (out) quickly terminates the on-cycle. in most cases, a short-time constant rc filter is required to filter out the leading-edge spike on the sense waveform. the amplitude and width of the leading edge depends on the gate capacitance, drain capacitance (including interwinding capacitance), and switching speed (mosfet turn-on time). set the rc time constant just long enough to suppress the leading edge. for a given design, measure the leading spike at the highest input and rated output load to determine the value of the rc filter. the low 305mv current-limit threshold reduces the power dissipation in the current-sense resistor. the current-limit threshold can be further reduced by adding a dc offset to the cs input from reg5 voltage. do not reduce the current-limit threshold below 150mv as it may cause noise issues. see figure 4. for a new value of the current-limit threshold (v ilim_low ), calculate the value of r1 using the following equation: cs ilim_low 4.75 r r1 0.290 v ? = applications information boost converter the max15004a/b/max15005a/b can be configured for step-up conversion. the boost converter output can be fed back to in through a schottky diode (see figure 5) so the controller can function during low voltage conditions such as cold-crank. use a schottky diode (d vin ) in the v in path to avoid backfeeding the input source. use the equations in the following sections to calculate inductor (l min ), input capacitor (c in ), and output capacitor (c out ) when using the converter in boost operation.inductor selection in boost coniguration using the following equation, calculate the minimum inductor value so that the converter remains in continuous mode operation at minimum output current (i omin ): 2 in min out out omin out d in out d ds omin o o vd l 2f v i where: v vv d v vv and i (0.1 i ) to (0.25 i ) ? ? = + = + = the higher value of i omin reduces the required inductance; however, it increases the peak and rms currents in the switching mosfet and inductor. use i omin from 10% to 25% of the full load current. the v d is the forward voltage drop of the external schottky diode, d is the duty cycle, and v ds is the voltage drop across the external switch. select the inductor with low dc resistance and with a saturation current (i sat ) rating higher than the peak switch current limit of the converter. figure 4. reducing current-sense threshold max15004a/bmax15005a/b reg5 0.3v current-limit comparator r s r cs c cs v in n r1 max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 15 downloaded from: http:///
input capacitor selection in boost conigurationthe input current for the boost converter is continuous and the rms ripple current at the input capacitor is low. calculate the minimum input capacitor value and maximum esr using the following equations: l in out q esr l in ds l out id c 4f v v esr i where : (v v ) d i lf ? ? = ? ? = ? ?= v ds is the total voltage drop across the external mosfet plus the voltage drop across the inductor esr. i l is peak-to-peak inductor ripple current as calculated above. v q is the portion of input ripple due to the capacitor discharge and v esr is the contribution due to esr of the capacitor. assume the input capacitor ripple contribu - tion due to esr (v esr ) and capacitor discharge (v q ) is equal when using a combination of ceramic and alu - minum capacitors. during the converter turn-on, a large current is drawn from the input source especially at high output to input differential. the max15004/max15005 are provided with a programmable soft-start, however, a large storage capacitor at the input may be necessary to avoid chattering due to finite hysteresis. output capacitor selection in boost coniguration for the boost converter, the output capacitor supplies the load current when the main switch is on. the required out - put capacitance is high, especially at higher duty cycles. also, the output capacitor esr needs to be low enough to minimize the voltage drop due to the esr while support - ing the load current. use the following equations to calcu - late the output capacitor, for a specified output ripple. all ripple values are peak-to-peak. figure 5. application schematic max15004a/bmax15005a/b in c vcc 4.7f d vbs d vin r cs d3 pgnd q l rs c out rb ra c vin 1f reg5 ss slope 11 6 13 1615 12 1 4 9 10 rt ct v cc out cs v out rtct comp c reg5 0.1f v in 18v c in c cs c ss c slope rf cf fb c ff max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 16 downloaded from: http:///
esr o o max out q out v esr i id c vf ? = = ? i o is the load current, v q is the portion of the ripple due to the capacitor discharge, and v esr is the contribution due to the esr of the capacitor. d max is the maximum duty cycle at the minimum input voltage. use a combination of low-esr ceramic and high-value, low-cost aluminum capacitors for lower output ripple and noise. calculating power loss in boost converter the max15004a/max15005a devices are available in a thermally enhanced package and can dissipate up to 1.7w at +70c ambient temperature. the total power dissipation in the package must be limited so that the junction temperature does not exceed its absolute maxi - mum rating of +150c at maximum ambient temperature; however, maxim recommends operating the junction at about +125c for better reliability. the average supply current (i drive-gate ) required by the switch driver is: drive gate g out i qf ? = where q g is total gate charge at 7.4v, a number available from mosfet data sheet. the supply current in the max15004a/b/max15005a/b is dependent on the switching frequency. see the typical operating characteristics to find the supply current i supply of the max15004a/b/max15005a/b at a given operating frequency. the total power dissipation (p t ) in the device due to supply current (i supply ) and the current required to drive the switch (i drivegate ) is calculated using following equation. t inmax supply drive gate p v (i i ) ? =+ mosfet selection in boost converter the max15004a/b/max15005a/b drive a wide variety of n-channel power mosfets. since v cc limits the out output peak gate-drive voltage to no more than 11v, a 12v (max) gate voltage-rated mosfet can be used with - out an additional clamp. best performance, especially at low-input voltages (5v in ), is achieved with low-threshold n-channel mosfets that specify on-resistance with a gate-source voltage (v gs ) of 2.5v or less. when select - ing the mosfet, key parameters can include: 1) total gate charge (q g ). 2) reverse-transfer capacitance or charge (c rss ). 3) on-resistance (r ds(on) ). 4) maximum drain-to-source voltage (v ds(max) ). 5) maximum gate frequencies threshold voltage (v th(max) ). at high switching, dynamic characteristics (parameters 1 and 2 of the above list) that predict switching losses have more impact on efficiency than r ds(on) , which predicts dc losses. q g includes all capacitances associated with charging the gate. the v ds(max) of the selected mosfet must be greater than the maximum output volt - age setting plus a diode drop. the 10v additional margin is recommended for spikes at the mosfet drain due to the inductance in the rectifier diode and output capacitor path. in addition, q g helps predict the current needed to drive the gate at the selected operating frequency when the internal ldo is driving the mosfet. slope compensation in boost coniguration the max15004a/b/max15005a/b use an internal ramp generator for slope compensation to stabilize the current loop when operating at duty cycles above 50%. it is advisable to add some slope compensation even at lower than 50% duty cycle to improve the noise immunity. the slope compensations should be optimized because too much slope compensation can turn the converter into the voltage-mode control. the amount of slope compensa - tion required depends on the downslope of the inductor current when the main switch is off. the inductor downslope depends on the input to output voltage differential of the boost converter, inductor value, and the switching frequen - cy. theoretically, the compensation slope should be equal to 50% of the inductor downslope; however, a little higher than 50% slope is advised. use the following equation to calculate the required compensating slope (mc) for the boost converter: ( ) 3 out in s (v v ) r 10 mc mv s 2l ? ? = the internal ramp signal resets at the beginning of each cycle and slews at the rate programmed by the external capacitor connected to slope. adjust the max15004a/b/ max15005a/b slew rate up to 110mv/s using the follow - ing equation: 9 slope 2.5 10 c mc(mv s) ? = where c slope is the external capacitor at slope in farads. max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 17 downloaded from: http:///
flyback converter the choice of the conversion topology is the first stage in power-supply design. the topology selection criteria include input voltage range, output voltage, peak currents in the primary and secondary circuits, efficiency, form fac - tor, and cost. for an output power of less than 50w and a 1:2 input voltage range with small form factor requirements, the flyback topology is the best choice. it uses a minimum of components, thereby reducing cost and form factor. the flyback converter can be designed to operate either in continuous or discontinuous mode of operation. in discontinuous mode of operation, the transformer core completes its energy transfer during the off-cycle, while in continuous mode of operation, the next cycle begins before the energy transfer is complete. the discontinuous mode of operation is chosen for the present example for the following reasons: it maximizes the energy storage in the magnetic com - ponent, thereby reducing size. simplifies the dynamic stability compensation design (no right-half plane zero). higher unity-gain bandwidth. a major disadvantage of discontinuous mode opera - tion is the higher peak-to-average current ratio in the primary and secondary circuits. higher peak-to-average current means higher rms current, and therefore, higher loss and lower efficiency. for low-power converters, the advantages of using discontinuous mode easily surpass the possible disadvantages. moreover, the drive capabil - ity of the max15004/max15005 is good enough to drive a large switching mosfet. with the presently available mosfets, power output of up to 50w is easily achievable with a discontinuous mode flyback topology using the max15004/max15005 in automotive applications. transformer design step-by-step transformer specification design for a dis - continuous flyback example is explained below. follow the steps below for the discontinuous mode trans - former: step 1) calculate the secondary winding inductance for guaranteed core discharge within a minimum off- time. step 2) calculate primary winding inductance for suf - ficient energy to support the maximum load. step 3) calculate the secondary and bias winding turns ratios. step 4) calculate the rms current in the primary and estimate the secondary rms current. step 5) consider proper sequencing of windings and transformer construction for low leakage. step 1) as discussed earlier, the core must be discharged during the off-cycle for discontinuous mode operation. the secondary inductance determines the time required to discharge the core. use the following equations to cal - culate the secondary inductance: ( ) ( ) out d offmin out out(max) off off on off v vd 2i f tt + where:d offmin = minimum d off . v d = secondary diode forward voltage drop. i out = maximum output rated current. step 2) the rising current in the primary builds the energy stored in the core during on-time, which is then released to deliver the output power during the off-time. primary inductance is then calculated to store enough energy during the on-time to support the maximum output power. 22 inmin max p out out(max) on on off vd l 2p f t d tt = = + d max = maximum d. max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 18 downloaded from: http:///
step 3) calculate the secondary to primary turns ratio (n sp ) and the bias winding to primary turns ratio (n bp ) using the following equations: ss sp pp bias bp p out nl n nl and n 11.7 n n v 0.35 = = = = + the forward bias drops of the secondary diode and the bias rectifier diode are assumed to be 0.35v and 0.7v, respectively. refer to the diode manufacturers data sheet to verify these numbers. step 4) the transformer manufacturer needs the rms current maximum values in the primary, secondary, and bias windings to design the wire diameter for the different windings. use only wires with a diameter smaller than 28awg to keep skin effect losses under control. to achieve the required copper cross-section, multiple wires must be used in parallel. multifilar windings are common in high-frequency converters. maximum rms currents in the primary and secondary occur at 50% duty cycle (minimum input voltage) and maximum output power. use the following equations to calculate the primary and secondary rms currents: out max prms max inmin out offmax srms offmax p d i 0.5 d v 3 id i 0.5 d 3 = ? = the bias current for most max15004/max15005 applica - tions is about 20ma and the selection of wire depends more on convenience than on current capacity. step 5) the winding technique and the windings sequence is important to reduce the leakage inductance spike at switch turn-off. for example, interleave the secondary between two primary halves. keep the bias winding close to the secondary, so that the bias voltage tracks the out - put voltage.mosfet selection mosfet selection criteria include the maximum drain voltage, peak/rms current in the primary and the maxi - mum-allowable power dissipation of the package without exceeding the junction temperature limits. the voltage seen by the mosfet drain is the sum of the input voltage, the reflected secondary voltage through trans - former turns ratio and the leakage inductance spike. the mosfets absolute maximum v ds rating must be higher than the worst-case (maximum input voltage and output load) drain voltage. p dsmax inmax out d spike s n v v (v v ) v n ?? = + + + ???? lower maximum v ds requirement means a shorter channel, lower r ds-on , lower gate charge, and smaller package. a lower n p /n s ratio allows a low v dsmax speci - fication and keeps the leakage inductance spike under control. a resistor/diode/capacitor snubber network can be also used to suppress the leakage inductance spike. the dc losses in the mosfet can be calculated using the value for the primary rms maximum current. switching losses in the mosfet depend on the operating frequency, total gate charge, and the transition loss during turn-off. there are no transition losses during turn-on since the primary current starts from zero in the discontinuous con - duction mode. mosfet derating may be necessary to avoid damage during system turn-on and any other fault conditions. use the following equation to estimate the power dissipation due to the power mosfet: 2 mos dson prms g in outmax inmax pk off outmax 2 ds ds outmax p (1.4 r i ) (q v f ) v it f () 4 cv f 2 = + + + where:q g = total gate charge of the mosfet (c) at 7.4v v in = input voltage (v) t off = turn-off time (s) c ds = drain-to-source capacitance (f) output filter designthe output capacitance requirements for the flyback con - verter depend on the peak-to-peak ripple acceptable at the load. the output capacitor supports the load current during the switch on-time. during the off-cycle, the trans - former secondary discharges the core replenishing the lost charge and simultaneously supplies the load current. the output ripple is the sum of the voltage drop due to charge loss during the switch on-time and the esr of the output capacitor. the high switching frequency of the max15004/ max15005 reduces the capacitance requirement. max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 19 downloaded from: http:///
an additional small lc filter may be necessary to suppress the remaining low-energy high-frequency spikes. the lc filter also helps attenuate the switching frequency ripple. care must be taken to avoid any compensation problems due to the insertion of the additional lc filter. design the lc filter with a corner frequency at more than a decade higher than the estimated closed-loop, unity- gain bandwidth to minimize its effect on the phase margin. use 1f to 10f low-esr ceramic capacitors and calcu - late the inductance using following equation: 32 c 1 l 4 10 f c where f c = estimated converter closed-loop unity-gain frequency. sepic converter the max15004a/b/max15005a/b can be configured for sepic conversion when the output voltage must be lower and higher than the input voltage when the input voltage varies through the operating range. the duty-cycle equa - tion: o in v d v 1d ? = indicates that the output voltage is lower than the input for a duty cycle lower than 0.5 while v out is higher than the input at a duty cycle higher than 0.5. the inherent advan - tage of the sepic topology over the boost converter is a complete isolation of the output from the source during a fault at the output. the sepic converter output can be fed back to in through a schottky diode (see figure 6) so the controller can function during low voltage conditions such as cold-crank. use a schottky diode (d vin ) in the v in path to avoid backfeeding the input source. the sepic converter design includes sizing of inductors, a mosfet, series capacitance, and the rectifier diode. the inductance is determined by the allowable ripple current through all the components mentioned above. lower ripple current means lower peak and rms currents and lower losses. the higher inductance value needed for a lower ripple current means a larger-sized inductor, which is a more expensive solution. the inductors l1 and l2 can be independent, however, winding them on the same core reduces the ripple currents. calculate the maximum duty cycle using the following equation and choose the rt and ct values accord - ingly for a given switching frequency (see the oscillator frequency/external synchronization section). out d max in min out d ds cs vv d v v v (v v ) ? ? ?? + = ?? ++ + ?? where v d is the forward voltage of the schottky diode, v cs (0.305v) is the current-sense threshold of the max15004/max15005, and v ds is the voltage drop across the switching mosfet during the on-time. inductor selection in sepic converter use the following equations to calculate the inductance values. assume both l1 and l2 are equal and that the inductor ripple current (i l ) is equal to 20% of the input current at nominal input voltage to calculate the induc - tance value. in min max 1 out l out max max l max vd l l l2 2f i 0.2 i d i (1 d ) ? ? ? ?? = = = ?? ? ?? ?? ?= ?? ?? where f out is the converter switching frequency and is the targeted system efficiency. use the coupled inductors msd-series from coilcraft or pf0553-series from pulse engineering, inc. make sure the inductor saturating current rating (i sat ) is 30% higher than the peak inductor current calculated using the following equation. use the current-sense resistor calculated based on the i lpk value from the equation below (see the current limit section). out max max lpk out max l max id i ii (1 d ) ? ? ? ?? = + +? ?? ?? max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 20 downloaded from: http:///
mosfet, diode, and series capacitor selection in a sepic converter for the sepic configuration, choose an n-channel mosfet with a v ds rating at least 20% higher than the sum of the output and input voltages. when operating at a high switching frequency, the gate charge and switch - ing losses become significant. use low gate-charge mosfets. the rms current of the mosfet is: 22 max mos rms lpk ldc lpk ldc d i (a ) (i ) (i ) (i i ) 3 ? ?? = + + ?? ?? where i ldc = (i lpk - i l ). use schottky diodes for higher conversion efficiency. the reverse voltage rating of the schottky diode must be high - er than the sum of the maximum input voltage (v in-max ) and the output voltage. since the average current flowing through the diode is equal to the output current, choose the diode with forward current rating of i out-max . the current sense (r cs ) can be calculated using the current- limit threshold (0.305v) of max15004/max15005 and i lpk . use a diode with a forward current rating more than the maximum output current limit if the sepic converter needs to be output short-circuit protected. cs lpk 0.305 r i = select r cs 20% below the value calculated above. calculate the output current limit using the following equation: ( ) out lim lpk l d i ii (1 d) ? ? ? ?? =? ???? where d is the duty cycle at the highest input voltage (v in-max ). the series capacitor should be chosen for minimum ripple voltage (v cp ) across the capacitor. we recommend using a maximum ripple v cp to be 5% of the minimum input voltage (v in-min ) when operating at the minimum input voltage. the multilayer ceramic capacitor x5r and x7r series are recommended due to their high ripple current capability and low esr. use the following equation to calculate the series capacitor cp value. out max max cp out id cp vf ? ?? = ?? ? ?? where v cp is 0.05 x v in-min . for a further discussion of sepic converters, go to http://pdfserv.maximintegrated.com/en/an/an1051. pdf . power dissipation the max15004/max15005 maximum power dissipation depends on the thermal resistance from the die to the ambient environment and the ambient temperature. the thermal resistance depends on the device package, pcb copper area, other thermal mass, and airflow. calculate the temperature rise of the die using following equation: t j = t c + (p t x jc ) or t j = t a + (p t x ja ) where jc is the junction-to-case thermal impedance (3c/w) of the 16-pin tssop-ep package and p t is power dissipated in the device. solder the exposed pad of the package to a large copper area to spread heat through the board surface, minimizing the case-to- ambient thermal impedance. measure the temperature of the copper area near the device (t c ) at worst-case condi - tion of power dissipation and use 3c/w as jc thermal impedance. the case-to-ambient thermal impedance ( ja ) is dependent on how well the heat is transferred from the pcb to the ambient. use a large copper area to keep the pcb temperature low. the ja is 38c/w for tssop-16-ep and 90c/w for tssop-16 package with the condition specified by the jedec51 standard for a multilayer board. max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 21 downloaded from: http:///
figure 6. sepic application circuit 16 15 max15005a/b ep 2 v cc out on/ off on off 5 n.c. 6 rtct 3 ovi 4 slope 1 in d3bat54c c vcc 1f rg 1 ? reg5 v out c36.8f c26.8f c16.8f c1100nf c76.8f d1ll4148 v in 2.5v to 16v v out reg5 sync d2 stp745g std20nf06l c622f v out (8v/2a) l1 l11 = l22 = 7.5mh c522f c422f r31.8k ? 14 pgnd c101f 13 reg5 12 cs r cs 100 ? c cs 100pf c347nf c4680pf r215k ? r s 0.025 ? r12.7k ? 11 comp 10 fb 9 ss c ss 150nf c slope 47pf r sync 10k? rt 15k? ct 150pf 7 sgnd 8 sync max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 22 downloaded from: http:///
layout recommendations typically, there are two sources of noise emission in a switching power supply: high di/dt loops and high dv/dt surfaces. for example, traces that carry the drain current often form high di/dt loops. similarly, the heatsink of the mosfet connected to the device drain presents a dv/dt source; therefore, minimize the surface area of the heat - sink as much as possible. keep all pcb traces carrying switching currents as short as possible to minimize cur - rent loops. use a ground plane for best results. careful pcb layout is critical to achieve low switch - ing losses and clean, stable operation. refer to the max15005 ev kit data sheet for a specific layout exam - ple. use a multilayer board whenever possible for better noise immunity. follow these guidelines for good pcb layout: 1) use a large copper plane under the package and solder it to the exposed pad. to effectively use this copper area as a heat exchanger between the pcb and ambient, expose this copper area on the top and bottom side of the pcb. 2) do not connect the connection from sgnd (pin 7) to the ep copper plane underneath the ic. use midlayer-1 as an sgnd plane when using a multilayer board. 3) isolate the power components and high-current path from the sensitive analog circuitry. 4) keep the high-current paths short, especially at the ground terminals. this practice is essential for stable, jitter-free operation. 5) connect sgnd and pgnd together close to the device at the return terminal of v cc bypass capacitor. do not connect them together anywhere else. 6) keep the power traces and load connections short. this practice is essential for high efficiency. use thick copper pcbs (2oz vs. 1oz) to enhance full-load efficiency. 7) ensure that the feedback connection to fb is short and direct. 8) route high-speed switching nodes away from the sensitive analog areas. use an internal pcb layer for sgnd as an emi shield to keep radiated noise away from the device, feedback dividers, and analog bypass capacitors. 9) connect sync pin to sgnd when not used. max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 23 downloaded from: http:///
figure 7. vfd flyback application circuit 16 15 max15005a/b ep 2 v cc out on/off 5 n.c. 6 rtct 3 ovi 4 slope 1 in r3 50? reg5 v anode c3 1f 16v c2 0.1mf 50v c1330f 50v v in (5.5v to 16v) reg5 n r2402k? 1% 14 pgnd c101f 13 reg5 v in 12 cs r5 1k? c9560pf c64700pf c747pf r13118k? 1% r60.06? 1% r141.3k? 1% 11 comp 10 fb 9 ss c80.1f c4 100pf r19 10k? r1 8.45k? 1% c5 1200pf 7 sgnd 8 ju1 1 2 sync r17 100k? 1% r18 47.5k? 1% r11 182k? 1% r12 12.1k? 1% r8 100k? d2 r7 510? c12 220pf c14 nu v anode (110v/55ma) filament+ (3v/650ma) filament- v grid (60v/12ma) r9 nu r10 36k? d2 r15 100? d5 d4 d1 c16330f 6.3v c1310f 200v c1522f 60v c17 2.2f 10v r16 10? c18 4700pf 100v c11 2200pf 100v r2 560? max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 24 typical operating circuits downloaded from: http:///
figure 8. boost application circuit 16 15 max15005a/b ep 2 v cc out on/ off 5 n.c. 6 rtct 3 ovi 4 slope 1 in r1 5 ? reg5 v out c101f/16v ceramic c11 0.1f c110f 25v v in (4.5v to 16v) reg5 sync qsi736dp r5100k? 14 pgnd c101f 13 reg5 v out 12 cs r3 1k? c4100pf c90.1f c8330pf r6136k? r40.025? r710k? 11 comp 10 fb 9 ss c70.1f c2 100pf r2 13k? c3 180pf 7 sgnd 8 ju1 1 2 sync r11 301k? r10 100k? r8 153k? r9 10k? d1 b340lb v out (18v/2a) c656f/25v svp-sanyo l110h/ihlp5050 vishay max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 25 typical operating circuits (continued) downloaded from: http:///
package type package code outline no. land pattern no. 16 tssop u16+2 21-0066 90-0117 16 tssop-ep u16e+3 21-0108 90-0120 1615 14 13 12 11 10 2 13 45 6 7 v cc outpgnd reg5 slope ovi on/ off in top view max15004amax15005a cs comp ep fb sgnd rtct 9 8 ss sync n.c. tssop-ep + 1615 14 13 12 11 10 2 13 45 6 7 v cc outpgnd reg5 slope ovi on/ off in max15004bmax15005b cs comp fb sgnd rtct 9 8 ss sync n.c. tssop + max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers www.maximintegrated.com maxim integrated 26 package information for the latest package outline information and land patterns (footprints), go to www.maximintegrated.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. chip information process: bicmos pin conigurations downloaded from: http:///
revision number revision date description pages changed 0 1/07 initial release 1 11/07 updated features , revised equations on pages 13, 20, and 21, revised figure 8 with correct mosfet, and updated package outline 1, 13, 20, 21, 25, 28 2 12/10 added max15005baue/v+ automotive part, updated features , updated package information , style edits 1C5, 9, 13, 21, 25C29 3 1/11 added MAX15004AAUE/v+, max15004baue/v+, max15005aaue/v+ automotive parts to the ordering information 1 4 1/15 updated beneits and features section 1 5 9/15 miscellaneous updates 1, 6, 9C11, 14C16, 18, 20C22 6 12/15 deleted last sentence in the startup operation/uvlo/on/ off section 12 maxim integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim integrated product. no circuit patent licenses are implied. maxim integrated reserves the right to change the circuitry and speciications without n otice at any time. the parametric values (min and max limits) shown in the electrical characteristics table are guaranteed. other parametric values quoted in this data sheet are provided for guidance. maxim integrated and the maxim integrated logo are trademarks of maxim integrated products, inc. max15004a/b-max15005a/b 4.5v to 40v input automotive flyback/boost/sepic power-supply controllers ? 2015 maxim integrated products, inc. 27 revision history for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim integrateds website at www.maximintegrated.com. downloaded from: http:///

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