1 description LT8711 micropower synchronous sepic converter demonstration circuit 2234a is a synchronous sepic converter featuring the lt ? 8711 multitopology switching controller. the LT8711 is a current mode pwm dc/dc controller with a dual input ldo to optimize gate driver efficiency. ultralow 15a quiescent current in low noise burst mode ? operation achieves high efficiency at very light loads and helps extend the run-time in battery pow - ered applications when in standby mode. the LT8711 switching frequency can be programmed either via oscil - lator resistor or external clock over a 100khz to 750khz range. the demo board regulates a 12v, 4a output from a 4.5v to 40v input source, and operates at 200khz switching frequency. the rated maximum load current is 4a, while derating is necessary for certain input voltage and thermal conditions. the sync pin on the demo board is grounded ( jp1 at burst position) by default for low ripple high efficiency burst mode operation at light load. to synchronize to an external clock, move jp1 to sync and apply the external clock to the sync turret. force continuous conduction mode can be selected by moving jp1 shunt to fcm posi - tion. l , lt, ltc, ltm, linear technology, burst mode and the linear logo are registered trademarks of analog devices, inc. all other trademarks are the property of their respective owners. p erformance s ummary the dc2234 a can be modified from a sepic converter to other topologies. synchronous boost and some other schematics are provided in the data sheet. please consult the factory or LT8711 data sheet for details regarding how to customize the dc2234 a or how to design different topologies for custom specifications. the LT8711 includes many other features such as user configurable under voltage lockout, soft-start, input volt - age feedforward regulation, and it is easily configured as synchronous buck, boost, sepic or nonsynchronous buck-boost converter. the data sheet gives a complete description of the device, operation and application information. the data sheet must be read in conjunction with this demo manual for dc2234 a. the LT8711 is assembled in a 20- lead plastic tssop package with a thermally enhanced ground pad. proper board layout is essential for maximum thermal performance. see the layout considerations section in the data sheet. design files for this circuit board are available at http://www.linear.com/demo/dc2234a specifications are at t a = 25c symbol parameter conditions min typ max units v in input voltage range 4.5 40 v v out output voltage 11.6 12 12.4 v i out maximum output current derating is necessary for certain v in and thermal conditions 4 a t sw switching frequency 185 200 215 khz eff efficiency at dc v in = 5v, i out = 1a v in = 12v, i out = 2a v in = 24v, i out = 4a v in = 36v, i out = 4a 91.9 92 91.4 90.2 % % % % dc2234af demo manual dc2234a
2 quick s tart p roce d ure dc2234 a is easy to set up to evaluate the performance of the LT8711. refer to figure 3 for proper measurement equipment setup and follow the 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. see figure 4 for the proper scope technique. 1. set an input power supply that is capable of 40v/12a. then turn off the supply . 2. with power off, connect the supply to the input termi - nals v in and gnd. 3. turn on the power at the input. note : make sure that the input voltage never exceeds 40v. 4. check for the proper output voltage of 12v . turn off the power at the input. 5. once the proper output voltage is established, connect a variable load capable of sinking 4a at 12v to the out - put terminals v out and gnd. set the current for 0a. a. if efficiency measurements are desired, an ammeter can be put in series with the output load in order to measure the dc2234as output current. b. a voltmeter can be placed across the output terminals in order to get an accurate output voltage measure- ment. 6. turn on the power at the input. note : if there is no output, temporarily disconnect the load to make sure that the load is not set too high. 7. once the proper output voltage is again established, adjust the load and/or input within the operating range and observe the output voltage regulation, ripple volt - age, efficiency and other desired parameters. 8. an external clock can be added to the sync termi - nal when sync function is used ( jp1 on the sync position). please ensure that the chosen rt sets the LT8711 switching frequency to equal or below the low - est sync frequency. see the data sheet section, clock synchronization. dc2234af demo manual dc2234a
3 quick s tart p roce d ure figure 2. dc2234a temperature rising vs input voltage figure 1. efficiency vs load current at 200khz switching frequency n-fet temperature rise p-fet temperature rise i out (a) 0 efficiency (%) 100 95 85 60 90 80 75 70 65 55 50 2 1 3 3.5 dc2234a f01 4 1.5 0.5 2.5 5v input 12v input 24v input 36v input input voltage (v) 0 temperature rising (c) 80 90 70 50 30 40 100 60 20 10 0 20 25 10 35 40 dc2234a f02 45 15 5 30 i out = 2a i out = 3a i out = 4a input voltage (v) 0 temperature rising (c) 120 80 40 100 60 20 0 20 25 10 35 40 45 15 5 30 i out = 2a i out = 3a i out = 4a dc2234af demo manual dc2234a
4 quick s tart p roce d ure figure 3. proper measurement equipment setup figure 4. measuring output ripple figure 5. dc2234a 12v input 2a to 4a load transient dc2234af demo manual dc2234a
5 p arts list item qty reference part description manufacturer/part number required circuit components 1 6 c2, c3, c4, cin2, cin3, cin4 cap, x7r, 10f, 50v, 10% 1210 murata, grm32er71h106ka12l 2 1 co1 alum, polymer, 270f, 16v, 20% panasonic, 16svpc270m 3 3 co2, co3, co4 cap, x7r, 22f, 25v, 10% 1210 murata, grm32er71e226ke15l 4 1 co7 cap, x7r, 10f, 25v, 10% 1206 murata, grm31cr71e106ka12l 5 1 c7 cap, x7r, 10nf, 25v, 10% 0603 murata, grm188r71e103ka01d 6 4 c11, c14, c18, c22 cap, x7r, 2.2f, 16v, 10% 0805 murata, grm21br71c225ka12l 7 1 c13 cap, x7r, 4.7f, 50v, 10% 1206 tdk, c3216x7r1h475k160ac 8 1 c15 cap, x7r, 4.7nf, 25v, 10% 0603 murata, grm188r71e472ka01d 9 1 c16 cap, c0g, 100pf, 50v, 5% 0603 tdk, c1608c0g1h101j080aa 10 1 c17 cap, x7r, 0.47f 16v 10% 0603 murata, grm188r71c474ka88d 11 1 c19 cap, x7r, 1000pf, 100v, 10% 1206 murata, grm319r72a102ka01d 12 1 d1 diode, 60v, 2a, powerdi-123 diodes inc, dfls260-7 13 1 d2 diode, 80v, 125ma, sod-523 diodes inc, 1n4148 wt- 7 14 1 l2 ind, 8.2h coilcraft, xal1510-822meb 15 1 l3 ind, 15h coilcraft, xal1510-153meb 16 1 mn1 n-mosfet, 80v, powerpak so-8 vishay, sir826adp-t1-ge3 17 1 mp1 p-mosfet, 60v, powerflat 5x6 stmicroelectronics, stl42p6llf6 18 2 r1, r3 res, sense, 0.002, 1.5w, 2%, krl3216 susumu, krl3216e-c-r002-g-t5 19 6 r5, r9, r12, r14, r18, r19 res, chip, 0, 0.1w, 0603 nic, nrc06zotrf 20 1 r6 res, chip, 3.3, 0.1w, 1%, 0603 vishay, crcw06033r30fkea 21 2 r7, r15 res, chip, 10, 0.1w, 1%, 0603 vishay, crcw060310r0fkea 22 1 r13 res, chip, 1m, 0.1w, 1%, 0603 vishay, crcw06031m00fkea 23 1 r16 res, chip, 71.5k, 0.1w, 1%, 0603 vishay, crcw060371k5fkea 24 2 r17,r23 res, chip, 100k, 0.1w, 1%, 0603 nic, nrc06f1003trf 25 1 r21 res, chip, 118k, 0.1w, 1%, 0603 nic, nrc06f1183trf 26 1 r22 res, chip, 49.9k, 0.1w, 1%, 0603 vishay, crcw060349k9fkea 27 1 r24 res, chip, 3.3, 1/2w, 5%, 1210 vishay, crcw12103r30jnea 28 1 u1 ic, LT8711efe 20-lead tssop linear tech, LT8711efe#pbf additional demo board circuit components 1 1 cin1 ep-cap, 56f, 50v, hvh series sun elect, 50hvh56m 2 0 cin5, cin6, co5, co6, c20(opt) cap, 1210 3 0 c1 (opt) cap, 2220 4 0 c6, c8, c9, c10, c12, c21(opt) cap, 0603 5 0 l1 (opt) ind, 8.2h 6 0 mn2 (opt) n-mosfet, powerpak so-8 7 0 mp2 (opt) p-mosfet, powerflat 5x6 8 0 r4 (opt) res, 1210 9 0 r20 (opt) res, 0603 dc2234af demo manual dc2234a
6 item qty reference part description manufacturer/part number hardware: for demo board only 1 11 e1 to e11 testpoint, turret, 0.094" mill-max, 2501-2-00-80-00-00-07-0 2 1 jp1 double row header 2 x 3 0.079" wurth elektronik, 62000621121 3 1 xjp1 shunt, 0.079" center wurth elektronik, 60800213421 4 4 mh1 to mh4 stand-off, nylon 0.50" tall keystone, 8833 (snap on) p arts list dc2234af demo manual dc2234a
7 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 5 5 4 4 3 3 2 2 1 1 d d c c b b a a 4.5v - 40v 12v / 4a pgnd vout pgnd vin agnd en/fbin sync 1. all resistors are 0603. all smd capacitors are 0603. note: unless otherwise specified (vin > 5v) intvcc intvcc e7 c9 opt co6 1210 + co1 270uf 16v 16svpc270m c17 470nf e4 r21 118k (200khz) cin2 10uf 50v 1210 c2 10uf 50v 1210 l3 15uh xal1510-153 r1 0.002 krl3216e r24 3.3 1210 co4 1210 25v l1b opt 3 2 c3 10uf 50v 1210 r20 opt u1 LT8711efe tg 10 extvcc 15 nc 18 fb 2 bg 11 isn 7 isp 6 bias 9 intvee 8 vc 3 ss 4 intvcc 13 vin 14 csn 16 csp 17 en/fbin 1 op mode 5 rt 20 sync 19 nc 12 gnd 21 e11 r4 opt 1210 r13 1m r17 100k r23 100k c8 opt c1 opt 2220 r19 0 c10 opt r9 0 mn1 sir826adp 4 5 3 6 2 1 7 8 d1 dfls260 e1 jp1 fcm burst sync 1 2 3 5 6 4 co3 e3 cin3 10uf 50v 1210 c16 100pf r15 10 r18 0 r14 0 l1a opt 1 4 e9 l2 8.2uh xal1510-822 c4 10uf 50v 1210 e10 r16 71.5k r6 3.3 c7 10nf c6 opt co5 opt d2 1n4148 sod-523 2 1 r22 49.9k mp2 opt c21 opt r5 0 c15 4.7nf co2 22uf e6 c13 4.7uf 50v 1206 c18 2.2uf 0805 r12 0 r7 10 c19 1nf 1206 100v + cin1 56uf 50v 50hvh56m cin6 opt 1210 mp1 stl42p6llf6 co7 10uf 25v 1206 cin4 10uf 50v 1210 mn2 opt 4 5 3 6 2 1 7 8 e8 e5 c20 opt 1210 r3 0.002 krl3216e c12 opt c14 2.2uf 0805 cin5 opt 1210 c22 2.2uf 0805 c11 2.2uf 0805 e2 rt ss isn en/fbin ng vc bias isp fb vout intvee vin vin sync bg dc2234af demo manual dc2234a
8 ? linear technology corporation 2017 lt 0917 ? printed in usa demonstration board important notice linear technology corporation (ltc) 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 ltc 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 party 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 ltc 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 whatsoeve r. ltc assumes no liability for applications assistance, customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind. ltc 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 ltc application engineer. mailing address: linear technology 1630 mccarthy blvd. milpitas, ca 95035 copyright ? 2004, linear technology corporation dc2234af demo manual dc2234a
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