1 application note 1636 author: paul orfanu isl85033-12veval3z wide v in negative v out buck-boost regulator with up to 5a output current hardware description the isl85033 is a wide input range, dual standard buck converter that can be configured to provide a negative output voltage. the isl85033-12veval3z evaluation board is used in this application note to demonstrate the negative configuration. in this configuration, v in can range from 4.5v to (28v - v out ). 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 - v out ) ? adjustable and synchronizable negative output voltage with continuous output current up to 5a, depending on v out and v in ? current mode control ? adjustable switching frequency from 300khz to 2mhz ? power-good detection (referenced to v out ) ? externally adjustable soft-start time ? overcurrent and hiccup mode short circuit protection, thermal overload protection, uvlo ? boot undervoltage detection ? default out-of-phase channels reduce voltage ripple and component size. user-selectable phase operation. recommended equipment the following materials are recommended to perform testing: ? 0v to 30v power supply with at least 7a source current capability or a 5v battery ? electronic loads capable of sinking current up to 7a ? digital multimeters (dmms) ? 100mhz quad-trace oscilloscope ? signal generator quick setup guide 1. ensure that the circuit is correctly connected to the supply and loads prior to applying any power. 2. connect the bias supply to vin1, the plus terminal to vin1, and the negative return to gnd1. 3. verify that the position is on for s1. 4. turn on the power supply. 5. verify the output voltage is -12v for v out . evaluating the other output voltages the isl85033-12veval3z kit output is preset to -12v; however, output voltages can be adjusted from -3.3v to -15v. the output voltage programming resistor, r3, depends on the desired output voltage of the regulator. the value for the feedback resistor is typically between 0 and 142k as shown in equation 1. table 1 summarizes the external component selection for v out = -5v, v out = -12v, and v out = -15v. the curves in figure 1 indicate the maximum output current the converter can deliver as a function of the input voltage and the selected output voltage configuration. figures 2, 3 and 4 show the efficiency for different v in , v out and load combinations. table 1. component selection for v out v out external components -5v r3 = 43.2k; r5 = 20k; c4 = 2.7nf c20 = 22f (1210 ceramic) c17 = 22f (1210 ceramic) c19 = 68f (15m ? polymer eefud0k680r) -12v r3 = 112k; r5 = 120k; c4 = 4.7nf c14, c17 = 22f (2210 ceramic) c12, c19 = 68f (70m ? tanbo2 tpsd686m020r0070) c20 = dnp -15v r3 = 142k; r5 = 120k; c4 = 4.7nf c14, c17 = 22f (2210 ceramic) c12, c19 = 68f (70m ? tanbo2 tpsd686m020r0070) c20 = dnp r3 r2 vout vfb -------------- 1 ? ?? ?? = (eq. 1) caution: these devices are sensitive to electrostatic discharge; follow proper ic handling procedures. copyright intersil americas inc. 2011. all rights reserved. 1-888-intersil or 1-888-468-3774 | intersil (and design) is a trademark owned by intersil corporation or one of its subsidiaries. all other trademarks mentioned are the property of their respective owners. july 27, 2011 an1636.1
application note 1636 2 an1636.1 july 27, 2011 if the output voltage desired is -0.8v, then r3 is shorted. the value for r2 is typically between 1k and 10k. note that if v out < |2.5v| (i.e., -0.8v), the switching frequency and compensation must be changed to accommodate the 300khz operation, due to minimum on-tim e limitation. please refer to the isl85033 data sheet for further information. frequency control the isl85033-12veval3z evaluation board has an fs pin that controls the frequency of oper ation. programm able frequency allows for optimization betw een efficiency and external component size. default switchin g frequency is 500khz when fs is tied to vcc (r9 = 0). by remo ving r9 and connecting r10 to the most negative potential on the board (v out ), the switching frequency could be changed from 300khz (r10 = 383k) to 2mhz (r10 = 40.2k). see the isl85033 data sheet for information about calculating the value of r10. do not leave this pin floating. disabling/enabling function the isl85033-12veval3z evaluation board contains an s1 switch that enables or disables both channels, thus allowing a low quiescent current state. table 2 details this function. note: if driven externally, the en signal (the same as all input logic signals) is referenced to v out (the most negative potential on the board) and not to gnd. th erefore, the source cannot be gnd referenced, and input level shifting is required. figure 1. isl85033-12veval3z buck boost: recommended maximum i out (v in ) figure 2. isl85033-12veval3z efficiency: v out = -15v figure 3. isl85033-12ve val3z efficiency: v out = -12v figure 4. isl85033-12veval3z efficiency: v out = -5v 0 1 2 3 4 5 6 5 7 9 11 13 15 17 19 21 23 25 v in (v) i out (a) v out = -5v v out = -12v v out = -15v 60 65 70 75 80 85 90 95 0 0.5 1.0 1.5 2.0 2.5 i out (a) v in = 5v v in = 12v efficiency (%) 0 0.5 1.0 1.5 2.0 2.5 i out (a) v in = 12v 60 65 70 75 80 85 90 95 efficiency (%) v in = 15v v in = 5v 60 65 70 75 80 85 90 95 0 0.5 1.0 1.5 2.0 2.5 i out (a) efficiency (%) v in = 12v v in = 15v v in = 5v v in = 6v table 2. switch settings s1 on/off control on enable v out off disable v out
application note 1636 3 an1636.1 july 27, 2011 isl85033-12veval3z schematic vneg -12v b340b b340b 10uh (adjustable) -12v vneg 10uh on off open 113k ss1 c3 pgood2 vneg 8.06k c13 isl85033irtz 68uf 0.01uf boot2 comp2 vin fb2 fs vin 10uf tbd pgood1 4700pf vneg vneg vcc dnp 100uf vcc 4.7uf vneg dnp 0.01uf open comp1 vcc ss2 vneg fs vneg syncin pgood2 dnp syncin 0 open 0 0 nc1 dnp ss2 comp2 vneg en open fb2 open ss1 vcc open 100k fb1 120k vneg dnp vneg vneg dnp 0 5600pf en vneg ss1 comp1 open open vneg open open pgood1 dnp 22uf 10uf 68uf ss1 boot1 vneg 22pf ss2 vneg 22uf fb1 en 10uf tbd vneg vneg 5600pf vneg u1 1 10 11 12 13 14 15 16 17 18 19 22 0 21 22 23 24 25 26 27 28 3 4 5 6 7 8 9 29 jvo2 2 3 4 1 vneg1 vneg2 vin gnd1 jlx2 2 3 4 1 gndo2 vneg ss2 pg1 fs si so pg2 en c11 jlx1 2 3 4 1 gndo1 r9 r18 d1 21 d2 21 r8 r7 r5 r11 c10 c4 c6 c8 r19 r20 c14 c17 s1 2 3 1 r17 r10 r25 r24 r23 r4 c9 c5 c7 c15 r2 r15 c16 r16 r3 r14 r13 r12 l2 1 2 c18 l1 12 c2 12 c12 12 c19 12 c20 c1 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 aa
application note 1636 4 an1636.1 july 27, 2011 bill of materials part number reference designator quantity value tolerance voltage power package type jedec type manufacturer description 131-4353-00 jlx1, jlx2, jvo2 3 conn tek131- 4353-00 tektronix scope probe test point pcb mount tpsd686k020r00 070-t c12, c19 2 68f 20% 20v smd cap_tant avx tqc series hi-volt low esr capacitor b340b d1, d2 2 smd2 do_sma diodes 3a low vf schottky barrier rectifier c5750x7r1e226m c14, c17 2 22f 20% 25v 2220 cap_2220 tdk ceramic cap eee-fk1v101p-t c2 1 100f 20% 35v smd capae_315x 402 panasonic al lytic fk series cap (rohs comp.) gmk325bj106kn c6, c8 2 10f 10% 35v 1210 cap_1210 taiyo yuden ceramic chip cap gt13mcbe s1 1 sw sw_gt13mc be c&k spdt on-off-on ultraminiature toggle switch h1044-00220- 50v5 c13 1 22pf 5% 50v 402 cap_0402 generic multilayer cap h1044-00472- 50v10 c4 1 4700pf 10% 50v 402 cap_0402 generic multilayer cap h1044-open c10, c15, c16 3 open open open 402 cap_0402 generic multilayer cap h1045-00103- 50v10 c5, c9 2 0.01f 10% 50v 603 cap_0603 generic multilayer cap h1045-00562- 50v10 c3, c11 2 5600pf 10% 50v 603 cap_0603 generic multilayer cap h1046-00475- 10v20 c7 1 4.7f 20% 10v 805 cap_0805 generic multilayer cap h1065-00106- 25v10-t c18 1 10f 10% 25v smd cap_1206 venkel multilayer cap h1082-tbd-tbd c1, c20 2 tbd tbd tbd 1210 c ap_1210 generic ceramic chip cap h2505-01003-1/ 16wr1 r4 1 100k 0.10% 1/16w 603 res_0603 generic metal film chip resistor h2505-dnp-dnp-1 r10, r17 2 dnp 1% dnp 603 res_0603 generic metal film chip resistor (do not populate) h2505-dnp-dnp- r1 r12, r13, r19, r20, r25 5 dnp 0.10% dnp 603 res_0603 generic metal film chip resistor (do not populate) h2510-01133- 1/16w1 r3 1 113k 1% 1/16w 402 res_0402 generic thick film chip resistor h2510-01203- 1/16w1 r5 1 120k 1% 1/16w 402 res_0402 generic thick film chip resistor h2510-08061- 1/16w1 r2 1 8.06k 1% 1/16w 402 res_0402 generic thick film chip resistor h2510-ropen- open r7, r8, r11, r14-r16 6 open 1% open 402 res_0402 generic thick film chip resistor h2511-00r00- 1/16w r23, r24 2 0 0% 1/16w 603 res_0603 generic thick film chip resistor h2511-00r00- 1/16w1 r9, r18 2 0 1% 1/16w 603 res_0603 generic thick film chip resistor isl85033irtz u1 1 qfn qfn28_157x 157_157_ep intersil wide vin dual standard buck regulator (pb-free) pad_100 en, fs, si, so, pg1, pg2, ss1, ss2, vneg 9 thole pad-100 generic 0.100 pad with 0.037 plated thru hole
application note 1636 5 an1636.1 july 27, 2011 pad_150 vin, gnd1, gndo1, gndo2, vneg1, vneg2 6 thole pad-150 generic 0.150 pad with 0.110 plated thru hole sq1004 l1, l2 2 10h 25% 4.8a smd ind_sq10xx falco smt shielded power inductor bill of materials (continued) part number reference designator quantity value tolerance voltage power package type jedec type manufacturer description isl85033-12veval3z layout figure 5. top layer components figure 6. top layer etch figure 7. second layer etch figure 8. third layer etch
application note 1636 6 intersil corporation reserves the right to make changes in circuit 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 an1636.1 july 27, 2011 figure 9. bottom layer etch figure 10. bottom layer components isl85033-12veval3z layout (continued)
|
