general description the max15032 constant-frequency, pulse-width-modu- lating (pwm), low-noise boost converter is intended for low-voltage systems that need a locally generated high voltage. this device is capable of generating low-noise, high output voltages, with an output power capability up to 600mw with a 2.9v input voltage. this device can be used for a wide variety of applications, such as pin or varactor diode biasing and lcd displays. the max15032 operates from +2.7v to +11v. the constant-frequency (500khz), current-mode pwm architecture provides low-noise output voltage that is easy to filter. a high-voltage internal lateral dmos power switch allows this device to boost output volt- ages up to 36v. the max15032 features a shutdown mode to save power. the max15032 is available in a small thermally enhanced 3mm x 3mm 8-pin tdfn package and is specified for operation over the -40? to +125? auto- motive temperature range. applications avalanche photodiode biasing pin diode bias supplies low-noise varactor diode bias supplies stb audio ic supplies lcd displays features ? input voltage range +2.7v to +5.5v (using internal charge pump) +5.5v to +11v ? wide adjustable output voltage range: (v in + 1v) to 36v ? output power: 600mw for v in 2.9v ? internal 0.5 (typ), 40v switch ? constant pwm frequency provides easy filtering in low-noise applications ? 500khz (typ) switching frequency ? 0.5? (max) shutdown current ? internal soft-start ? small thermally enhanced 3mm x 3mm 8-pin tdfn package max15032 500khz, 36v output, 600mw pwm step-up dc-dc converter ________________________________________________________________ maxim integrated products 1 1 + 34 865 pgnd cn in max15032 2 7 cp lx fb shdn gnd tdfn top view pin configuration ordering information max15032 in v in = 2.7v to 5.5v v out 36v shdn pgnd lx fb cp cn gnd r1 d1 l1 r2 c in c out c cp typical operating circuit 19-4232; rev 0; 8/08 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. part temp range pin- package top mark max15032ata+t -40? to +125? 8 tdfn-ep* +bkp + denotes a lead-free/rohs-compliant package. t = tape and reel. * ep = exposed pad.
max15032 500khz, 36v output, 600mw pwm step-up dc-dc converter 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v in = +3.3v, v shdn = +3.3v, c in = 10?, pgnd = gnd = 0v, t a = t j = -40? to +125?, unless otherwise noted. typical values are at t a = +25?. see the typical operating circuit .) (note 2) stresses beyond those listed under ?bsolute 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. note 1: package thermal resistances were obtained using the method described in jedec specification jesd51-7, using a four- layer board. for detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial. in to gnd ...............................................................-0.3v to +12v lx to pgnd ............................................................-0.3v to +40v fb to gnd ..............................................................-0.3v to +12v shdn to gnd ..............................................-0.3v to (v in + 0.3v) cn to gnd .............................................................-0.3v to +12v cp to gnd..............................................................-0.3v to +12v pgnd to gnd .......................................................-0.3v to +0.3v continuous power dissipation (t a = +70?) 8-pin tdfn (derate 24.4mw/? above +70?) ......1951.2mw junction-to-case thermal resistance ( jc ) (note 1) ........8?/w junction-to-ambient thermal resistance ( ja ) (note 1) ........................................................................41?/w operating temperature range .........................-40? to +125? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units supply voltage c cp = 10nf 2.7 5.5 supply voltage range v in cp connected to in 5.5 11 v v fb = 1.4v (no switching), c cp = 10nf, v in = 3.3v 12 supply current i in v fb = 1.4v (no switching), cp = in, v in = 11v 1.5 3 ma undervoltage lockout v uvlo v in rising 2.375 2.5 2.675 v undervoltage lockout hysteresis v uvlo-hys 100 mv shutdown current i shdn v shdn = 0v 0.5 ? logic input ( shdn ) shdn input low level v il 0.8 v shdn input high level v ih 2.0 v boost converter output voltage adjustment range v in + 1 36 v switching frequency f sw 450 500 550 khz fb set point v fb 1.214 1.245 1.276 v fb input bias current i fb 300 na v in = 2.9v, v cp = 5.5v 0.42 1 c cp = 10nf, i lx = 100ma v in = 5.5v, v cp = 10v 0.33 1 v in = v cp = 5.5v 0.42 1 lx switch on-resistance r ds_on cp connected to in, i lx = 100ma v in = v cp = 11v 0.33 1 peak switch current limit i lim_lx 1 1.33 1.7 a lx leakage current v lx = 36v 2 a line regulation i load = 2ma 0.25 %
max15032 500khz, 36v output, 600mw pwm step-up dc-dc converter _______________________________________________________________________________________ 3 note 2: all devices are 100% production tested at room temperature (t a = +25?). all parameter limits through the temperature range are guaranteed by design. parameter symbol conditions min typ max units load regulation i load = 0 to 20ma, v out = 30v 1 % soft-start duration 8ms soft-start steps (0.25 x i lim_lx ) to i lim_lx 32 steps thermal protection thermal shutdown rising +160 ? thermal-shutdown hysteresis 8 c electrical characteristics (continued) (v in = +3.3v, v shdn = +3.3v, c in = 10?, pgnd = gnd = 0v, t a = t j = -40? to +125?, unless otherwise noted. typical values are at t a = +25?. see the typical operating circuit .) (note 2) efficiency vs. load current max15032 toc01 load current (ma) efficiency (%) 18 16 12 14 4 6 8 10 2 40 45 50 55 60 65 70 75 80 85 35 020 v out = 36v v in = 5v v out = 36v v in = 3.3v efficiency vs. load current max15032 toc02 load current (ma) efficiency (%) 18 16 12 14 4 6 8 10 2 40 45 50 55 60 65 70 75 80 85 35 020 v out = 30v v in = 5v v out = 30v v in = 3.3v efficiency vs. load current max15032 toc03 load current (ma) efficiency (%) 45 40 30 35 10 15 20 25 5 40 45 50 55 60 65 70 75 80 85 35 050 v out = 24v v in = 5v v out = 24v v in = 3.3v typical operating characteristics (v in = 3.3v, l1 = 4.7?, r1 = 143k , r2 = 6.2k , c in = 10?, c out = 2.2?, c cp = 10nf, see the typical operating circuit . t a = +25?, unless otherwise noted.)
max15032 500khz, 36v output, 600mw pwm step-up dc-dc converter 4 _______________________________________________________________________________________ efficiency vs. load current max15032 toc04 load current (ma) efficiency (%) 45 40 30 35 10 15 20 25 5 40 45 50 55 60 65 70 75 80 85 90 35 050 v out = 12v v in = 3.3v v out = 12v v in = 5v l = 3.3 h maximum load current vs. input voltage max15032 toc05 input voltage (v) maximum load current (ma) 10 9 7 8 4 5 6 3 30 60 90 120 150 180 210 240 270 300 330 360 0 211 l = 4.7 h for v out = 36v, 30v, and 24v v out = 12v l = 3.3 h v out = 24v v out = 30v v out = 36v minimum startup voltage vs. load current max15032 toc06 load current (ma) minimum startup voltage (v) 18 16 12 14 4 6 8 10 2 2.35 2.40 2.45 2.50 2.55 2.60 2.65 2.70 2.75 2.80 2.30 020 v out = 30v supply current vs. supply voltage max15032 toc07 supply voltage (v) supply current (ma) 10 9 3 4 5 7 6 8 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 0 211 v fb = 1.4v supply current vs. temperature max15032 toc08 temperature ( c) supply current (ma) 110 95 65 80 -10 5 20 35 50 -25 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 0.50 -40 125 v fb = 1.4v switching frequency vs. temperature max15032 toc09 temperature ( c) switching frequency (khz) 110 95 65 80 -10 5 20 35 50 -25 460 470 480 490 500 510 520 530 540 550 450 -40 125 v in = 5v exiting shutdown max15032 toc10 1ms/div v shdn 2v/div v out 10v/div i l 500ma/div v in = 5v i out = 1ma entering shutdown max15032 toc11 20ms/div v shdn 2v/div v out 10v/div v in = 5v i out = 1ma switching waveforms max15032 toc12 1 s/div v out (ac-coupled) 50mv/div v lx 20v/div i l 500ma/div i out = 20ma typical operating characteristics (continued) (v in = 3.3v, l1 = 4.7?, r1 = 143k , r2 = 6.2k , c in = 10?, c out = 2.2?, c cp = 10nf, see the typical operating circuit . t a = +25?, unless otherwise noted.)
max15032 500khz, 36v output, 600mw pwm step-up dc-dc converter _______________________________________________________________________________________ 5 load-transient response max15032 toc13 100ms/div v out (ac-coupled) 200mv/div i out 5ma/div rise time = 10ns line-transient response max15032 toc14 2ms/div v in 1v/div v out (ac-coupled) 50mv/div i out = 1ma fb voltage vs. temperature max15032 toc15 temperature ( c) fb voltage (v) 110 95 -25 -10 5 35 50 65 20 80 1.22 1.23 1.24 1.25 1.26 1.27 1.28 1.29 1.21 -40 125 switch on-resistance vs. temperature max15032 toc16 temperature ( c) switch on-resistance (m ) 110 95 65 80 -10 5 20 35 50 -25 450 500 550 600 650 700 750 800 850 900 950 1000 400 -40 125 v in = 5v lx leakage current vs. temperature max15032 toc17 temperature ( c) lx leakage current (na) 110 95 65 80 -10 5 20 35 50 -25 5 10 15 20 25 30 35 40 45 50 0 -40 125 v lx = 36v shutdown supply current vs. temperature max15032 toc18 temperature ( c) shutdown supply current (na) 110 95 65 80 -10 5 20 35 50 -25 30 60 90 120 150 180 210 240 270 300 0 -40 125 v shdn = 0v output voltage vs. load current max15032 toc19 load current (ma) output voltage (v) 18 16 12 14 4 6 8 10 2 29.55 29.60 29.65 29.70 29.75 29.80 29.85 29.90 29.95 30.00 29.50 020 v in = 3.3v v in = 5v v out vs. optimum inductor value max15032 toc20 l optimum ( h) v out (v) 4.7 3.3 12 18 24 30 36 42 6 v in = 2.7v to 11v typical operating characteristics (continued) (v in = 3.3v, l1 = 4.7?, r1 = 143k , r2 = 6.2k , c in = 10?, c out = 2.2?, c cp = 10nf, see the typical operating circuit . t a = +25?, unless otherwise noted.)
max15032 500khz, 36v output, 600mw pwm step-up dc-dc converter 6 _______________________________________________________________________________________ pin description pin name function 1lx drain of internal 40v n-channel dmos. connect inductor/diode to lx. minimize trace area at lx to reduce switching noise emission. 2 gnd signal ground. connect directly to the local ground plane. connect gnd to pgnd at a single point, typically near the output capacitor return terminal. 3fb feedback regulation point. connect to the center tap of a resistive divider from the output (v out ) to gnd to set the output voltage. the fb voltage regulates to 1.245v (typ). 4 shdn active-low shutdown control input. a logic-low voltage on shdn shuts down the device and reduces the supply current to 0.5? (max). connect shdn to in for always-on operation. do not connect shdn to a voltage higher than v in . 5 in input supply voltage. bypass in to pgnd with a 4.7? minimum ceramic capacitor. 6cn negative terminal of the charge-pump flying capacitor for 2.7v to 5.5v supply voltage operation. leave cn unconnected when the input voltage is in the +5.5v to +11v range. 7cp positive terminal of the charge-pump flying capacitor for 2.7v to 5.5v supply voltage operation. connect to in when the input voltage is in the +5.5v to +11v range. 8 pgnd power ground. connect the input and output filter capacitors?negative terminal to pgnd. connect externally to gnd at a single point, typically at the output capacitor return terminal. ?p exposed pad. connect ep to a large copper plane at the gnd potential to improve thermal dissipation. do not use as the main gnd connection. functional diagram n max15032 +a -c -a +c clk v ref shdn v ref lx pgnd fb gnd cn cp in switch control logic soft- start oscillator 500khz charge pump (doubler) bias and reference thermal shutdown switch current sense uvlo
max15032 500khz, 36v output, 600mw pwm step-up dc-dc converter _______________________________________________________________________________________ 7 detailed description the max15032 constant-frequency, current-mode, pulse-width-modulating (pwm) boost converter is intended for low-voltage systems that often need a locally generated high voltage. this device is capable of generating low-noise, high-output voltage required for pin and varactor diode biasing and lcd displays. the max15032 operates either from +2.7v to +5.5v or from +5.5v to +11v. for +2.7v to +5.5v operation, an internal charge pump with an external 10nf ceramic capacitor is used. the max15032 also features a shut- down logic input to disable the device and reduce its standby current to 0.5? (max). the max15032 operates in discontinuous mode in order to reduce the switching noise caused by the reverse recovery charge of the rectifier diode. other continuous mode boost converters generate large voltage spikes at the output when the lx switch turns on because there is a conduction path between the output, diode, and switch to ground during the time needed for the diode to turn off and reverse its bias voltage. to reduce the out- put noise even further, the lx switch turns off by taking 6.8ns typically to transition from ?n?to ?ff.?as a consequence, the positive slew rate of the lx node is reduced and the current from the inductor does not ?orce?the output voltage as hard as would be the case if the lx switch were to turn off more quickly. also, the constant-frequency (500khz) pwm architec- ture generates an output voltage ripple that is easy to filter. a 40v lateral dmos device used as the internal power switch makes the device ideal for boost convert- ers with output voltages up to 36v. the max15032 can also be used in other topologies where the pwm switch is grounded, like sepic and flyback. pwm controller the heart of the max15032 current-mode pwm con- troller is a bicmos multi-input comparator that simulta- neously processes the output-error signal and switch current signal. the main pwm comparator is direct summing, lacking a traditional error amplifier and its associated phase shift. the direct summing configura- tion approaches ideal cycle-by-cycle control over the output voltage since there is no conventional error amplifier in the feedback path. the device operates in pwm mode using a fixed-fre- quency, current-mode operation. the current-mode fre- quency loop regulates the peak inductor current as a function of the output error signal. the current-mode pwm controller is intended for discontinuous conduc- tion mode (dcm) operation. no internal slope compen- sation is added to the current signal. shutdown ( shdn ) the max15032 features an active-low shutdown input ( shdn ). pull shdn low to enter shutdown. during shut- down, the supply current drops to 0.5 a (max). however, the output remains connected to the input through the inductor and output rectifier, holding the output voltage to one diode drop below v in when the max15032 shuts down. connect shdn to in for always-on operation. charge pump at low supply voltages (+2.7v to +5.5v), an internal charge-pump circuit and an external 10nf ceramic capacitor double the available supply voltage in order to drive the internal switch efficiently. in the +5.5v to +11v supply voltage range, the charge pump must be disabled by connecting cp to in and leaving cn unconnected. design procedure setting the output voltage set the max15032 output voltage by connecting a resistive divider from the output to fb to gnd (see the typical operating circuit ). select r2 (fb to gnd resis- tor) between 6k and 10k . calculate r1 (v out to fb resistor) with the following equation: where v fb = 1.245v (see the electrical characteristics table) and v out can range from (v in + 1v) to 36v. rr v v out fb 12 1 = ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
max15032 determining peak inductor current if the boost converter remains in the discontinuous mode of operation, then the approximate peak inductor current, i lpeak (a), is represented by the formula below: where t s is the period in ?, v out is the output voltage in volts, v in_min is the minimum input voltage in volts, i out is the output current in amperes, l is the inductor value in ?, and is the efficiency of the boost converter. determining the inductor value three key inductor parameters must be specified for operation with the max15032: inductance value (l), inductor saturation current (i sat ), and dc series resis- tance (dcr). in general, the inductor should have a saturation current rating greater than the maximum switch peak current-limit value (i lim-lx(max) = 1.7a). dcr should be below 0.1 for reasonable efficiency. due to the high switching frequency of the max15032, inductors with a ferrite core or equivalent are recom- mended to minimize core losses. table 1 shows a list of vendors with 4.7? inductor parts. table 1. inductor vendors use the following formula to calculate the lower bound of the inductor value at different output voltages and output currents. this is the minimum inductance value for discontinuous mode operation for supplying the full 600mw output power: where v in (v), v out (v), and i out (a) are typical val- ues, t s (?) is the period, is the efficiency, and i lim-lx is the peak lx current (a). calculate the optimum value of l (l optimum ) to ensure the full output power without reaching the boundary between continuous conduction mode (ccm) and dcm using the following formula: where: for a design in which v in = 3.3v, v out = 30v, i out = 20ma, = 0.7, and t s = 2?, l optimum = 4.7?: l max = 10.5? and l min = 3.3? for a worst-case scenario in which v in = 2.9v, v out = 30v, i out = 20ma, = 0.7, i lim-lx(min) = 1a, and t s = 1.8?: l max = 9.2? and: l min = 2.2? the choice of 4.7? is reasonable given the worst-case scenario above. in general, the higher the inductance, the lower the switching noise. diode selection the max15032? high switching frequency demands a high-speed rectifier. schottky diodes are recommend- ed for most applications because of their fast recovery time and low forward-voltage drop. ensure that the diode? peak current rating is greater than the inductor peak current. also, the diode reverse breakdown volt- age must be greater than v out . output filter capacitor selection for most applications, use a small ceramic surface-mount output capacitor, 2.2? or greater. to achieve low output ripple, a capacitor with low-esr, low-esl, and high- capacitance value should be selected. if tantalum or electrolytic capacitors are used to achieve high capaci- tance values, always add a small ceramic in parallel to bypass the high-frequency components of the diode cur- rent. the higher esr and esl of electrolytic increase both the output ripple and peak-to-peak transient voltage. assuming the contribution from the esr and capacitor lh vvv t i max in min out in min s out [] () __ = ? 2 2 v v out 2 l lh optimum max = [] . 225 lh ti v v i min s out out in min lim lx [] () _ = ? ? 2 2 i tv v i l lpeak s out in min out = ? 2( ) _ 500khz, 36v output, 600mw pwm step-up dc-dc converter 8 _______________________________________________________________________________________ vendor phone fax part number of 4.7? inductor tdk 408-437-9585 408-437-9591 slf7045t- 4r7m2r0-pf toko 847-297-0070 847-699-7864 636cy-4r7m+p3 coilcraft 800-322-2645 847-639-1469 mos6020-472mlc
discharge equals 50% (proportions could vary), calcu- late the output capacitance and esr required for a spec- ified ripple using the following equations: for very low output-ripple applications, the output of the boost converter can be followed by an rc filter to fur- ther reduce the ripple. figure 1 shows a 10 , 2.2? fil- ter used to reduce the switching output ripple to 1mv p-p with a 20ma output and a ripple voltage of 400? p-p with a 2ma load. the output voltage regula- tion resistive divider must remain connected to the diode/output capacitor node. x7r ceramic capacitors are stable over -40? to +125? temperature range. where the automotive tem- perature range is required, use x7r ceramic capaci- tors. x5r dielectric can be used for -40? to +85? applications. input capacitor selection bypass in (the input voltage pin) to pgnd with a mini- mum 4.7? ceramic capacitor. depending on the sup- ply source impedance, higher values might be needed. make sure that the input capacitor is close enough to the ic to provide adequate decoupling at in as well. if the layout cannot achieve this, add another 0.1? ceramic capacitor between in and pgnd in the imme- diate vicinity of the ic. bulk aluminum electrolytic capacitors might be needed to avoid chattering at low input voltages. in the case of aluminum electrolytic capacitors, calculate the capacitor value and esr of the input capacitor using the following equations: applications information layout considerations careful pcb layout is critical to achieve clean and sta- ble operation. protect sensitive analog grounds by using a star ground configuration. connect gnd and pgnd together close to the device at the return terminal of the output bypass capacitor. do not connect them together anywhere else. keep all pcb traces as short as possible to reduce stray capacitance, trace resis- tance, and radiated noise. ensure that the feedback connection to fb is short and direct. route high-speed switching nodes away from the sensitive analog areas. avoid any coupling from lx to fb node by keeping the fb node away from the lx routing. in addition, decou- pling lx and fb with a small 22pf capacitor from fb to gnd can be used. use an internal pcb layer for gnd as an emi shield to keep radiated noise away from the device, feedback dividers, and bypass capacitors. cf vi vv t i in out out in min in s lpea [] . _ = ? 05 k k optimum out in min out in min lv vvv ? ? ? ? ? ? ? __ () ? ? ? = esr m vv vi in in min out out [] . _ ? 05 cf i v t il v out out out s lpeak optimum o [] .( = ? 05 u ut in min out out v esr m v i ? ? ? ? ? ? ? ? ? = _ ) [] . 05 max15032 500khz, 36v output, 600mw pwm step-up dc-dc converter _______________________________________________________________________________________ 9 figure 1. typical operating circuit with rc filter max15032 in v in = 2.9v to 5.5v v out 30v shdn pgnd lx fb cp cn gnd r1 143k d1 1a/40v l1 4.7 h r2 6.2k c in 10 f c out 2.2 f c cp 10nf c f 2.2 f r f 10
max15032 500khz, 36v output, 600mw pwm step-up 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. 10 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2008 maxim integrated products is a registered trademark of maxim integrated products, inc. chip information process: bicmos package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . package type package code document no. 8 tdfn t833-2 21-0137
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