1 description ltc 3374euhf 8-channel parallelable 1a buck dc/dc demonstration circuit 1953 a is an 8- output power supply featuring the lt c ? 3374 . the ltc3374 has eight synchro- nous buck regulators each with an independent v in supply. up to four buck regulators may be paralleled together to create a higher power buck regulator with a single induc - tor. the input range of the ltc3374 is ideal for single cell li-ion/polymer batter y applications. the buck regulators can be enabled via external preci - sion threshold enable pins to allow hardwired power up sequences. l , lt, ltc, ltm, linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. p erformance s ummary the ltc3374 has a default operating frequency of 2mhz or it can be set between 1 mhz and 3 mhz using an external resistor. the ltc3374 also has a sync pin which allows the internal oscillator to synchronize to an external clock from 1mhz to 3mhz. refer to the ltc3374 data sheet for more details on the electrical and timing specifications. design files for this circuit board are available at http://www . linear.com/demo/dc1953a specifications are at t a = 25c parameter conditions min typ max units input supply range (v in1-8 ) 2.25 5.5 v v cc 2.7 5.5 v v out1 v in1 > 3.3v, i vout1 0a to 1a 3.3 v v out2 v in2 > 3.0v, i vout2 0a to 1a 3.0 v v out3 v in3 > 2.5v, i vout3 0a to 1a 2.5 v v out4 i vout4 0a to 1a 2.0 v v out5 i vout5 0a to 1a 1.8 v v out6 i vout6 0a to 1a 1.5 v v out7 i vout7 0a to 1a 1.2 v v out8 i vout8 0a to 1a 1.0 v dc1953afa demo manual dc1953a
2 quick s tart p roce d ure the dc1953a is easy to set up to evaluate the performance of the ltc3374. refer to figure 1 and figure 2 for proper measurement equipment setup and follow the evaluation procedure below. note: when measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. measure the input or output voltage ripple by touching the probe tip directly across the vin or vout and gnd terminals. see figure 2 for proper scope probe technique. 1. set the jp1-jp8 jumpers on the dc1953a board to the off position. 2. set the mode jumper, jp9, to the burst position. 3. with power off, connect a 0 v to 6v, 100 ma power supply to vcc and gnd with a voltmeter as shown in figure?1. 4. with power off, connect a 0 v to 6v, 3 a power supply to each vin and gnd with a series ammeter and a voltmeter as shown in figure 1. a single 0 v to 6v, 10a supply can be used instead to supply all vin inputs simultaneously. 5. turn on and set the vcc input power supply to 3.3v and turn on and set the vin1 supply to 5v. note: make sure that the input voltages do not exceed 6v. 6. set the jp1 jumper, en1, to the on position and observe the vout1 regulator turns on and the pgood_all led extinguishes. note: all regulators not powered or set up as a slave must have their en pins tied to gnd to allow the pgood_all led to extinguish. 7. with power off, connect a 0 v to 3 a load to each vout and gnd with a series ammeter and a voltmeter as shown in figure 1. 8. slowly increase load1 from 0 a to 1 a and observe the output voltage. the output ripple may also be observed using an oscilloscope with the probe con - nected as shown in figure 2. 9. whe n done evaluating vout1, repeat steps 5 through 8 for each regulator. 10. refer to the ltc3374 data sheet for more details on how the ltc3374 operates. 11. when done, turn off all loads and power supplies. dc1953afa demo manual dc1953a
3 quick s tart p roce d ure figure 1. proper measurement equipment setup figure 2. measuring input or output ripple vin gnd dc1953afa demo manual dc1953a
4 c ombining b uck r egulators with m ultiple o utput f ilters c ombining b uck r egulators with a s ingle o utput f ilter the ltc3374 has the ability to combine up to 4 consecu- tively numbered bucks to achieve output currents of 1a, 2a, 3 a or 4 a. the easiest way to configure the dc1953a with combined outputs is to use an output inductor and output capacitor on each switch node. while combining stages with multiple filters is not ideal for performance or minimization of components, it does provide the easiest way to prototype with the desired current levels. follow the steps below to make an output a slave to the adjacent regulator: 1. remove the desired slave regulators associated fb resistors and feed forward capacitor. 2. add the associated 0 resistor to tie the fb pin to its vin pin. 3. connect the outputs together at the output capacitors. 4. connect the vin of the slave regulator to the vin of the master regulator. for example, to make regulator 2 a slave of regulator 1: 1. remove r6, r7 and c16. 2. solder a 0 resistor to r5. 3. connect vin1 to vin2 at the vin terminals. 4. connect vout1 to vout2 at the output capacitors c12 and c17. regulator 3 can also be combined with regulator 1 and regulator 2 to create a 3a output by: 1. removing fb3 components, r10, r11 and c19. 2. solder a 0 resistor to r9. 3. connect vin3 to vin2 and vin1 at the vin terminals. 4. connect vout3 to vout2 and vout1 at the output capacitors. regulator 4 can also be added to this combination by following the same steps with regulator 4 s associated components. the higher number regulator is always a slave to the ad- jacent lower number regulator; therefore regulator 1 can never be a slave and regulator 8 can never be a master. in most applications it is more practical to use a single output filter on a combined regulator. to do this the switch nodes of the combined regulators need to be shorted together, and the output inductor and capacitor need to be sized correctly. please refer to the combined buck regulator section in the ltc3374 data sheet for more information on sizing the output capacitor and inductor. note: the dc1953a layout was optimized for eight 1a outputs. for applications with combined regulators the layout should be optimized for the components used, the lowest and equal impedance on the combined switch nodes, and the shortest ac current paths as possible. to combine regulators 1 and 2 for a 2a output, perform the following steps and refer to figure 3: 1. remove l2, r6, r7 and c16. 2. add a 0 resistor to r5. 3. replace l1 with an inductor that can handle the 2a output at current limit. 4. replace c12 with at least a 47f ceramic capacitor. 5. short sw1 and sw2 together. to reduce the impedance on the sw node, cut the excess trace from sw2 to l2 close to the short as possible. 6. short vin1 and vin2 together near the vin terminals. dc1953afa demo manual dc1953a
5 c ombining b uck r egulators with a s ingle o utput f ilter to combine regulators 2, 3 and 4 for a 3 a output, perform the following steps and refer to figure 4: 1. remove l2, l3 and l4. 2. add copper foil between the l2 and l3 sw node pads. refer to figure 5 for steps 2 thru 5. note: copper foil does not provide as low thermal or electri - cal impedance as pcb copper traces. an optimized layout should be fabricated to accurately evaluate a 3a output. 3. add copper foil between vout2 and vout3 nodes at the location needed for the inductor pad. the solder mask may need to be scraped away to do this. figure 3. combined 2a output regulators 1 and 2 4. short sw3 and sw4 together. 5. cut excess sw4 node between short and the l4 pad. 6. remove r10, r11, r15, r17, c19 and c23. 7. add 0 resistors to r9 and r14. 8. c 17 and c 20 must have at least 33 f ceramic capacitors. 9. connect vin2, vin3 and vin4 together at the vin terminals. figure 4. combined 3a output regulators 2, 3, 4 dc1953afa demo manual dc1953a
6 c ombining b uck r egulators with a s ingle o utput f ilter to combine regulators 1, 2, 3, and 4 for a 4 a output per- form the following steps and refer to figure 6: 1. remove l1, l2, l3 and l4. 2. add copper foil between the l2 and l3 sw node pads. refer to figure 7 for steps 2 thru 5. note: an optimized layout should be fabricated to accurately evaluate a 4a output. 3. add copper foil between vout2 and vout3 nodes at the location needed for the inductor pad. the solder mask may need to be scraped away to do this. 4. short sw1 and sw2 together then short sw3 and sw4 together. 5. cut excess sw1 node between the short and the l1 pad then cut the excess sw4 node between the short and the l4 pad. figure 5. copper foil between l2 and l3, modified sw4 trace 6. remove r6, r7, r10, r11, r15, r17, c16, c19 and c23. 7. add 0 resistors to r5, r9 and r14. 8. re place c 17 and c 20 with at least 47 f ceramic capacitors. 9. connect tp1b with tp2b with a 26 awg wire. this connects the 4a output voltage to the fb1 network. note: do not connect the load on the vout1 terminal. the 4 a output will be observed on the vout1 terminal, however it is only connected via the 26 awg wire and 10 mil fb traces. connect the load to the vout2 and/or vout3 terminals instead. 10. connect vin1, vin2, vin3 and vin4 together at the vin terminals. dc1953afa demo manual dc1953a
7 c ombining b uck r egulators with a s ingle o utput f ilter figure 6. combined 4a output, regulators 1, 2, 3 and 4 figure 7. copper foil between l2 and l3, modified sw1 & sw4 traces dc1953afa demo manual dc1953a
8 p arts l ist item qty reference part description manufacturer/ part number required circuit components 1 9 c1, c2, c3, c4, c5, c6, c7, c8, c14 cap, chip, x5r, 10f, 20%, 6.3v, 0603 tdk, c1608x5r0j106m 2 8 c12, c17, c20, c24, c28, c30, c32, c34 cap, chip, x5r, 33f, 20%, 6.3v, 0805 tdk, c2012x5r0j336mt 3 8 l1-l8 ind, smt, 2.2h, 21m, 20%, 3.7a, 4mmx4mm coilcraft, xfl4020-222m 4 3 r2, r10, r47 res, chip, 1.02m, 1%, 1/16w, 0402 vishay, crcw04021m02fked 5 1 r3 res, chip, 324k, 1%, 1/16w, 0402 vishay, crcw0402324kfked 6 2 r6, r15 res, chip, 1.00m, 1%, 1/16w, 0402 vishay, crcw04021m00fked 7 1 r7 res, chip, 365k, 1%, 1/16w, 0402 vishay, crcw0402365kfked 8 1 r11 res, chip, 475k, 1%, 1/16w, 0402 vishay, crcw0402475kfked 9 1 r17 res, chip, 665k, 1%, 1/16w, 0402 vishay, crcw0402665kfked 10 2 r22, r32 res, chip, 806k, 1%, 1/10w, 0402 vishay, crcw0402806kfked 11 1 r25 res, chip, 649k, 1%, 1/10w, 0402 vishay, crcw0402649kfked 12 1 r30 res, chip, 715k, 1%, 1/10w, 0402 vishay, crcw0402715kfked 13 1 r37 res, chip, 232k, 1%, 1/16w, 0402 vishay, crcw0402232kfked 14 1 r39 res, chip, 464k, 1%, 1/16w, 0402 vishay, crcw0402464kfked 15 1 r44 res, chip, 255k, 1%, 1/16w, 0402 vishay, crcw0402255kfked 16 1 u1 8-channel parallelable 1a buck dc/dcs linear tech., LTC3374EUHF additional demo board circuit components 17 9 c9, c10, c13, c15, c18, c21, c22, c25, c26 cap, chip, x5r , 22f, 20%, 6.3v, 0805 t aiyo yuden, jmk212abj226mg 18 8 c11, c16, c19, c23, c27, c29, c31, c33 cap, chip, npo, 10pf, 5%, 50v, 0402 avx , 04025a100 jat 19 1 d1 diode, led, super red diff, 0603 smd lumex, sml-lx0603 srw -tr 20 8 r1, r4, r8, r12, r20, r27, r34, r42 res, chip, 20 , 1%, 1/16w, 0402 vishay, crcw040220r0fked 21 11 r13, r18, r23, r26, r31, r35, r40, r45, r48, r52, r53 res, chip, 1k, 5%, 1/16w, 0402 vishay, crcw04021k00jned 22 0 r5, r9, r14, r21, r29, r36, r43 res, chip, 0 jumper, 1/10w, 0603 ( opt ) vishay, crcw06030000z0ed 23 10 r16, r19, r24, r28, r33, r38, r41, r46, r49, r51 res, chip, 2.40m, 5%, 1/16w, 0402 vishay, crcw04022m40jned 24 0 r50 res, chip, 402k, 1%, 1/16w, 0402 ( opt ) vishay, crcw0402402kfked 25 1 r52 res, chip, 470, 5%, 1/16w, 0402 vishay, crcw0402470rjned 26 1 r54 res, chip, 0 jumper, 1/16w, 0402 vishay, crcw04020000z0ed hardware-for demo board only 27 27 e1-e15, e17, e18, e20, e21, e23-e25, e27, e29, e31, e33, e35 turret, 0.09" dia mill-max, 2501-2-00-80-00-00-07-0 28 13 e16, e19, e22, e26, e28, e30, e32, e34, e36-e40 turret, 0.061" dia mill-max, 2308-2-00-80-00-00-07-0 29 9 jp1-jp9 2mm to header 1x3 , 2mm samtec, tmm-103-02-l-s 30 9 jp1-jp9 shunt, 2mm samtec, 2sn-kb-g 31 4 stand-off nylon, 0.375" tall (snap-on) keystone, 8832 (snap on) 32 1 fa b , printed circuit board dc1953a-3 dc1953afa demo manual dc1953a
9 information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. s chematic diagram dc1953afa demo manual dc1953a
10 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com ? linear technology corporation 2013 lt 0315 rev a ? printed in usa demonstration board important notice linear technology corporation ( lt c ) provides the enclosed product(s) under the following as is conditions: this demonstration board ( demo board) kit being sold or provided by linear technology is intended for use for engineering development or evaluation purposes only and is not provided by lt c for commercial use. as such, the demo board herein may not be complete in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety measures typically found in finished commercial goods. as a prototype, this product does not fall within the scope of the european union directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations. if this evaluation kit does not meet the specifications recited in the demo board manual the kit may be returned within 30 days from the date of delivery for a full refund. the foregoing warranty is the exclusive warranty made by the seller to buyer and is in lieu of all other warranties, expressed, implied, or statutory, including any warranty of merchantability or fitness for any particular purpose. except to the extent of this indemnity, neither p arty shall be liable to the other for any indirect, special, incidental, or consequential damages. the user assumes all responsibility and liability for proper and safe handling of the goods. further, the user releases lt c from all claims arising from the handling or use of the goods. due to the open construction of the product, it is the users responsibility to take any and all appropriate precautions with regard to electrostatic discharge. also be aware that the products herein may not be regulatory compliant or agency certified (fcc, ul, ce, etc.). no license is granted under any patent right or other intellectual property whatsoever. lt c assumes no liability for applications assistance, customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind. lt c currently services a variety of customers for products around the world, and therefore this transaction is not exclusive. please read the demo board manual prior to handling the product . persons handling this product must have electronics training and observe good laboratory practice standards. common sense is encouraged. this notice contains important safety information about temperatures and voltages. for further safety concerns, please contact a lt c applica- tion engineer. mailing address: linear technology 1630 mccarthy blvd. milpitas, ca 95035 copyright ? 2004, linear technology corporation dc1953afa demo manual dc1953a
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