1 application note 1585 ISL85033EVAL2Z (small form) wide vin dual standard buck regulator with 3a/3a output current - short form description the ISL85033EVAL2Z kit demonstrates performance of the isl85033 switching regulator ic. an input range of 4.5v to 28v and 3a output per channel (connect in parallel to 6a) allows the isl85033 to meet a wide variety of pol requirements. the isl85033 is offered in a 4mmx4mm 28 ld tqfn package with 1mm maximum height. the complete converter occupies 6.25cm 2 area. key features ? wide input voltage range from 4.5v to 28v ? adjustable output voltage with continuous output current up to 3a per channel ? current mode control ? adjustable switching frequency from 300khz to 2mhz ? independent power-good detection ? selectable in-phase or out-of-phase pwms switching operation ? independent, sequential, ratiometric or absolute tracking between outputs ? internal 2ms soft-start time ? overcurrent and hiccup mode short circuit protection, thermal overload protection, uvlo ? boot undervoltage detection ? channels are out-of-phase, reducing voltage ripple and component size quick setup guide 1. ensure correct board connection to the supply (?+? to vin1 and ?-? to gnd2) and loads prior to applying power, then turn on the power supply. 2. verify the output voltage is 5v for v out1 and 3.3v for v out2. frequency control isl85033 has an fs pin that controls the frequency of operation. programmable frequency allows for optimization between efficiency and external component size. isl85033e val2z has the switching frequency set to 500khz (fs is tied to vcc). sync control the isl85033 has a si pin for external synchronization. default board configuration has r8 = 0 to gnd, which defaults to the internally se lected switching frequency. removing r8 allows the synchronization to be external between 600khz to 4mhz. do not leave this pin floating. output voltage selection ISL85033EVAL2Z board has v out1 set to 5v and v out2 set to 3.3v. the output voltage programming resistor, r 3 (r 10 respectively), will depend on the value chosen for the feedback resistor, r 2 (r 12 respectively), and the desired output voltage, v out , see equation 1. the value for r 2 (r 12 respectively) is typically between 1k and 10k. please note that if v out is less than 2.5v, switching frequency and compensation must be changed for 300khz operation due to minimum on-time limitation. please refer to data sheet fn6676 for further information. figure 1. efficiency vs load, t a = +25c, v in = 28v figure 2. ISL85033EVAL2Z top layer components 40 50 60 70 80 90 100 0.0 0.5 1.0 1.5 2.0 2.5 3.0 output load (a) efficiency (%) 3.3v out 500khz 9v out 1mhz 12v out 1mhz 1.8v out 300khz 5v out 500khz 1.629? 0.595? (eq. 1) r 3 v out1 ( v fb ) r 2 0.8 ? ? ? = r 10 v out2 ( v fb ) r 12 0.8 ? ? ? = author: paul orfanu november 29, 2010 an1585.1 caution: these devices are sensitive to electrostatic discharge; follow proper ic handling procedures. 1-888-intersil or 1-888-468-3774 | copyright inte rsil americas inc. 2010. all rights reserved intersil (and design) is a trademark owned by in tersil corporation or one of its subsidiaries. all other trademarks mentioned are the property of their respective owners.
2 intersil corporation reserves the right to make changes in circui t design, software and/or specifications at any time without n otice. accordingly, the reader is cautioned to verify that the application note or technical brief is current before proceeding. for information regarding intersil corporation and its products, see www.intersil.com an1585.1 november 29, 2010 figure 3. ISL85033EVAL2Z schematic figure 4. ISL85033EVAL2Z top layer etch figure 5. ISL85033EVAL2Z bottom layer components sgnd if vout1=5v (4.5v-5.5v) pls populate r26 only if vout2=5v (4.5v-5.5v) pls populate r27 only otherwise pls leave r26, r27 dnp! vout1=5v vout2=3.3v vout1 69.8k u1 c14 47uf 7uh 13 14 vin2 d2 pgood2 comp2 2 1 l2 2 1 l1 gnd3 vo2 gnd4 gnd2 vin1 1 2 1 2 d1 c7 r13 r14 r10 r3 r12 c16 c1 r11 r1 r2 c11 c6 c9 c5 c12 r15 r16 r17 r18 r7 c3 c10 c8 c4 c13 r9 r4 r5 r6 r8 vo1 c2 c15 gnd1 29 9 8 7 6 5 4 3 28 27 26 25 24 23 22 21 20 19 18 17 16 15 12 11 10 1 7uh vout2 boot1 b340b syncin isl85033irtz vin2 0 ss1 boot2 06/21/2010 fb1 vcc b340b vout1 12pf open dnp fb2 ss2 ss2 fb1 vin2 vin1 0 10uf 4.7uf 10uf vin1 10uf wide vin dual s comp1 syncout 42.2k dnp dnp dnp vcc 12pf 470pf comp2 tim klemann 47uf 25.5k 0 68pf nc1 0 69.8k paul orfanu isl8503 3 0 0 syncin ss2 ss1 fb2 vout2 paul orfanu vcc pgood1 comp1 8.06k 0.01uf 470pf 68pf dnp ss1 open 8.06k 0.01uf dnp 06/23/2010 2 updated by: title: engineer: date: date: date: drawn by: released by: a ep ss1 pgnd1 phase1 pgood1 nc fs syncin sgnd syncout pgood2 comp2 fb2 ss2 pgnd2 boot2 phase2 phase2 vin2 vin2 en2 vcc en1 vin1 vin1 phase1 fb1 boot1 comp1 a a a a a a a a a a a a a a aa a a a a a a a sql004 sql004 1.500? 1.875? application note 1585
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