1 description lt 8640 42v, 5a micropower synchronous step-down silent switcher demonstration circuit 2202 a is a 42v, 5 a micropower synchronous step-down silent switcher ? with spread spectrum frequency modulation featuring the lt ? 8640. the demo board is designed for 5 v output from a 5.7v to 42 v input. the wide input range allows a variety of input sources, such as automotive batteries and industrial supplies. the LT8640 is a compact, ultralow emission, high efficiency, and high speed synchronous monolithic step - down switching regulator. the integrated power switches and inclusion of all necessary circuitry reduce the components count and solution size. special silent switcher architecture minimizes emi/ emc emissions. selectable spread spectrum mode can further improve emi/emc performance. ultralow 2.5 a quiescent current in burst mode ? operation achieves high efficiency at very light loads. fast minimum on-time of 40 ns enables high v in to low v out conversion at high frequency. the LT8640 switching frequency can be programmed either via oscillator resistor or external clock over a 200 khz to 3mhz range. the sync pin on the demo board is grounded (jp1 at burst position) by default for low ripple burst mode operation. to synchronize to an external clock, move jp1 to sync and apply the external clock to the sync tur- ret. spread spectrum mode and pulse-skipping mode can be selected respectively by moving jp1 shunt. figure 1 shows the efficiency of the circuit at 12 v and 24 v input in burst mode operation ( input from v in turret pin). figure 2 l , lt, ltc, ltm, linear technology, the linear logo, burst mode and silent switcher are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. p erformance s ummary shows the LT8640 temperature rising on dc2202a demo board under different load conditions. the rated maximum load current is 5 a, while derating is necessary for certain input voltage and thermal conditions. the demo board has an emi filter installed. the emi performance of the board ( with emi filter) is shown on figure 3. the red line in figure 3 is cispr25 class 5 peak limit. the figure shows that the circuit passes the test with a wide margin. to achieve emi/emc performance as shown in figure 3, the input emi filter is required and the input voltage should be applied at vemi turret pin. an inductor l2, which is a 0 jumper on the board by default now, can be added in the emi filter to further reduce the conducted emission. the LT8640 data sheet gives a complete description of the part, operation and application information. the data sheet must be read in conjunction with this demo manual for demo circuit 2202 a. the LT8640 is assembled in a 3mm 4 mm plastic qfn package with exposed pads for low thermal resistance. proper board layout is essential for both low emi operation and maximum thermal perfor - mance. see the data sheet sections low emi pcb layout and thermal considerations and peak output current. design files for this circuit board are available at http://www .linear.com/demo/dc2202a specifications are at t a = 25c symbol parameter conditions min typ max units v in input supply range 5.7 42 v v out output voltage 4.85 5 5.15 v i out maximum output current derating is necessary for certain v in and thermal conditions 5 a f sw switching frequency 1.85 2 2.15 mhz efe efficiency at dc v in = 12v , i out = 3a 93.7 % dc2202af demo manual dc2202a
2 quick s tart p roce d ure load current (a) 60 efficiency (%) 70 100 65 75 80 90 85 95 1.5 dc2202a f01 5 10.5 2 3.5 4.5 32.5 4 v in = 12v v in = 24v v out = 5v f sw = 2mhz sync/mode = gnd input voltage (v) 10 temperature rising (c) 40 100 30 20 50 60 80 70 90 18 dc2202a f02 42 126 24 3530 v out = 5v f sw = 2mhz i out = 5a i out = 4.5a i out = 4a i out = 3.5a amplitude (dbv/m) 40 45 50 35 30 25 20 15 10 ?5 0 5 frequency (mhz) 0 900 100 200 300 500 400 600 700 800 1000 amplitude (dbv/m) 40 45 50 35 30 25 20 15 10 ?5 0 5 frequency (mhz) 0 900 100 200 300 500 400 600 700 800 1000 dc2202a demo board (with emi filter installed) 14v input to 5v output at 4a, f sw = 2mhz dc2202a f03 class 5 peak limit burst mode spread spectrum mode horizontal polarization peak detector class 5 peak limit burst mode spread spectrum mode vertical polarization peak detector figure 1. LT8640 demo circuit dc2202a efficiency vs load current (input from v in turret pin) figure 2. LT8640 demo circuit dc2202a temperature rising vs input voltage figure 3. LT8640 demo circuit dc2202a emi performance in cispr25 radiated emission test (14v input from vemi turret pin, i out = 4a) dc2202af demo manual dc2202a
3 quick s tart p roce d ure demonstration circuit 2202 a is easy to set up to evalu- ate the performance of the LT8640. refer to figure 4 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. measure the input or output voltage ripple by touching the probe tip directly across the v in or v out and gnd terminals. see figure 5 for the proper scope technique. 1. place jp1 on burst position. 2. with power off, connect the input power supply to v emi and gnd. if the emi/emc performance is not important, the input emi filter can be bypassed by connecting the input power supply to v in and gnd. 3. with power off, connect the load from v out to gnd. 4. turn on the power at the input. note: make sure that the input voltage does not exceed 42v. 5. check for the proper output voltage (v out = 5v). note: if there is no output, temporarily disconnect the load to make sure that the load is not set too high or is shorted. 6. once the proper output voltage is established, adjust the load within the operating ranges and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 7. an external clock can be added to the sync terminal when sync function is used ( jp1 on the sync position). please make sure that rt should be chose to set the LT8640 switching frequency equal to or below the low - est sync frequency. jp1 can also set LT8640 in spread spectrum mode ( jp1 on the spread- spectrum position) or pulse-skipping mode ( jp1 on the pulse- skipping position). figure 4. proper measurement equipment setup v out gnd figure 5. measuring output ripple dc2202af demo manual dc2202a
4 p arts list item qty reference part description manufacturer/ part number required circuit components 1 2 c2, c12 cap., x5r, 1f, 50v, 10% 0603 tdk, c1608x5r1h105k 2 2 c4, c8 cap., x7r, 0.1f, 16v, 10% 0603 murata, grm188r71c104ka01d 3 1 c5 cap., c0g, 10pf, 25v, 0.25p 0603 avx , 06033a100 cat 2a 4 1 c6 cap., x5r, 100f, 10v, 20% 1210 samsung, cl32a107mpvnnne 5 2 c7, c9 cap., x7r, 1.0f, 25v, 10% 0603 murata, grm188r71e105ka12d 6 1 c11 cap., x5r, 10f, 50v, 10% 1206 tdk, c3216x5r1h106k 7 1 c13 cap., x5r, 4.7f, 25v, 10% 0603 murata, grm188r61e475ke11d 8 1 l1 inductor,1.5h w rth elektronik, 74437346015 8 2 r1, r3 res., chip., 100k, 1/10w, 1% 0603 vishay, crcw0603100kfkea 9 1 r2 res., chip., 18.2k, 1/10w, 1% 0603 vishay, crcw060318k2fkea 10 1 r4 res., chip., 1m, 1/10w, 1% 0603 vishay, crcw06031m00fkea 11 1 r5 res., chip., 243k, 1/10w, 1%, 0603 vishay, crcw0603243kfkea 12 1 u1 ic, regulator, 20-qfn, udc linear tech. corp., LT8640eudc#pbf additional demo board circuit components 1 1 c1 cap., alum 22f, 63v sun elect., 63ce22bs 2 2 c3, c10 cap., x7r, 10f, 50v, 10% 1210 murata, grm32er71h106ka12l 3 1 c14 cap., x7r, 0.1f, 50v, 10% 0402 tdk, c1005x7r1h104k 4 1 fb1 chip bead w rth elektronik, 74279226101 5 1 l2 res., chip., 0 , 3/4w, 2010 visha y, crcw20100000z0ef 6 0 r6 ( opt ) res., 0603 7 1 r7 res., chip., 0, 1/10w, 0603 vishay, crcw06030000z0ea hardware: for demo board only 1 10 e1-e10 testpoint, turret, .094" pbf mill-max, 2501-2-00-80-00-00-07-0 2 1 jp1 24, 0.079 double row header w rth elektronik, 62000821121 3 1 xjp1 shunt, 0.079" center w rth elektronik, 60800213421 4 4 mh1-mh4 stand-off, nylon 0.50" tall w rth elektronik, 702935000 dc2202af demo manual dc2202a
5 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 all capacitors are 0603. notes: unless otherwise specified 1. all resistors are 0603. suncon 63ce22bs (2mhz) ** ** ** c2 should be placed between vin1 and gnd1. c12 should be placed between vin2 and gnd2. these capacitors must be placed as close as possible to LT8640. * * see demo manual sync burst spread-spectrum pulse-skipping vout vin vin e3 vout 5v / 5a r2 18.2k l1 1.5uh 74437346015 fb1 74279226101 e9 gnd e10 vemi c7 1uf 25v e2 gnd c12 1uf 50v r4 1meg c13 4.7uf jp1 1 2 3 5 7 4 6 8 c14 0.1uf 0402 50v e8 pg e5 sync r7 0 r3 100k + c1 22uf 63v c3 10uf 50v 1210 c9 1uf c2 1uf 50v e4 gnd e7 tr/ss c11 10uf 50v 1206 e1 vin 5.7v - 42v r1 100k r5 243k c6 100uf 10v 1210 l2 0 2010 c10 10uf 50v 1210 c5 10pf c8 0.1uf e6 en/uv r6 opt u1 LT8640eudc vin1 4 en/uv 14 sync 17 intvcc 2 rt 15 fb 20 pg 19 bias 1 sw 9 sw 8 bst 3 sw 21 gnd1 6 gnd2 10 tr/ss 16 gnd1 7 gnd2 11 vin2 13 gnd 18 sw 22 c4 0.1uf 16v dc2202af demo manual dc2202a
6 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com ? linear technology corporation 2015 lt 0215 ? 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 dc2202af demo manual dc2202a
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