demo board quick start guide dc425 1mhz sy nchronous buck-boost converter ltc3440 description demonstration circuit dc425 is a con- stant-frequency synchronous buck- boost converter using the ltc3440. the input range is from 2.5v to 5.5v, making it ideal for single-cell lith- ium-ion or three-cell nicd/nimh bat- tery applications. this converter provides up to 95% efficiency, much higher than traditional buck-boost converters. for 2.5v minimum input voltage, this converter can provide up to 500ma load current. the output voltage is set at 3.3v. a different output voltage in the range of 2.5v to 5.5v can be obtained by changing one of the feedback resis- tors. the frequency is set at 1mhz, which is a good trade-off between efficiency and size. the frequency can be modified by changing r6 or by synchronizing to an external clock. in shutdown, the board draws about 2.5 a, where 2 a goes through the 1m ? pull up resistor (r4) and the ic it- self draws less than 1 a. gerber files for this circuit board are available. call the ltc factory. quick start guide refer to figure 1 for the connection diagram and follow the procedure be- low: 1. apply a voltage source to the input of the circuit between the v in and gnd terminals. the circuit will start up at input voltage higher than 2.5v. n o te do not apply more than 5.5v to the input. 2. attach a voltmeter or oscilloscope probe between the v out and gnd ter- minals of the circuit to monitor the output. to start the circuit, the shunt at jp1 needs to be put in run position. 3. attach a load to the output. the available output current depends on the input voltage. 1
demo board quick start guide dc425 1mhz sy nchronous buck-boost converter + ? + ? load + ? fixed freq. burst mode shdn run jp2 jp1 +? +? +? gnd vin vout gnd sync dc425 l tc3440ems 1mhz syncronous buck-boost figure 1. dc425 hookup diagram 2
demo board quick start guide dc425 1mhz sy nchronous buck-boost converter performance summary p a r a m e t e r c o n d i t i o n v a l u e input voltage range 2.5v to 5.5v maximum load current, min v out = 3.3v, v in = 2.5v 500ma typical output ripple v out = 3.3v, i out = 500ma 13mv p - p typical operating frequency r6 = 62k 1mhz typical performance characteristics 1000 10 100 60 efficiency (%) load current (ma) 100 80 70 90 4.2v 3.6v 3.0v 2.7v figure 2. efficiency vs. load current (without external schottky diodes) 3
5 5 4 4 3 3 2 2 1 1 d d c c b b a a burst mode linear technology c orp fixed frequency notes: unless otherwise spe cified 1. all resistors are in ohms, 0402. 2. install shunts on jp1 and jp2 pin 2 and 3. run shdn DC425A-2*ltc3440ems a 1 630 mccarthy blvd. milpitas, ca 95035 ph. (408) 954-8400 fax (408) 434-0507 1 1 a thursday, november 29, 2001 1mhz synchronous b uck-boost ltc confidential-for customer use only title size document number rev date: sheet of sync vout shdn vin vin c4 330pf c5 opt 10pf e4 vout 3.3v @500ma jp1 1 3 2 r4 1m jp2 1 3 2 e2 gnd e3 sync c6 0.047uf e5 gnd e1 vin 2.5v to 5.5v c1 10uf 6.3v 1206 c7 1uf 6.3v 0603 d1 zhcs400 opt zetex 1 2 u1 ltc3440ems 8 6 1 2 3 4 7 5 9 10 shdn/ss vout rt mode/sync sw1 sw2 vin gnd fb vc l1 10uh su mida cdrh4d28-100 1 2 d2 zhcs400 opt zetex 1 2 r6 62k r1 340k 1% c3 220pf r5 2.2k c2 22uf 6.3v 1210 r2 200k 1% r3 15k
linear technology corporation ltc3440 bill of materials DC425A-2 item qty reference part description manufacture / part # 1 1 c1 cap., x5r 10uf 6.3v,20%,1206 taiyo yuden jmk316bj106ml 2 1 c2 cap., x5r 22uf 6.3v,1210 taiyo yuden, jmk325bj226mm 3 1 c3 cap., npo 220pf 25v avx 04023a221kat1a 4 1 c4 cap., x7r, 330pf 50v avx 04025c331mat1a 5 0 c5 cap., npo 10pf 50v opt 6 1 c6 cap., x5r, 0.047uf 10v avx 0402zd473mat1a 7 1 c7 cap., x5r 1uf 6.3v,20%,0603 taiyo yuden jmk107bj105ma 8 0 d1,d2 diode, schottky,sod323 opt zetex zhcs400 9 5 e1-e5 tp, turret, .094" mill-max 2501-2 10 2 jp1,jp2 header, 3pin 1 row .079cc comm-con 2802s-03-g1 11 2 shunts for jp1,jp2 shunt, .079" center comm-con ccij2mm-138g 12 1 l1 ind, 10uh, l-cdrh4d28 sumida cdrh4d28-100 13 1 r1 res, chip 340k, 1% aac cr05-3403fm 14 1 r2 res, chip 200k, 1% aac cr05-2003fm 15 1 r3 res, chip 15k, 5% aac cr05-153jm 16 1 r4 res, chip 1m, 5% aac cr05-106jm 17 1 r5 res, chip 2.2k, 5% aac cr05-222jm 18 1 r6 res, chip 62k, 5% aac cr05-623jm 19 1 u1 ic, ltc3440ems, msop10 linear tech. ltc3440ems page 1 425a bom.xls
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