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1 dc1768af demo manual dc1768a description LTC3626EUDC 20v, 2.5a synchronous monolithic step-down regulator with current and temperature monitoring demonstration circuit 1768a is a step-down converter, using the ltc3626 monolithic synchronous buck regulator, which has current and temperature monitoring capabilities. the 1768a has an input voltage range of 3.6v to 20v, and is capable of delivering up to 2.5a of output current. the output voltage of the 1768a can be set as low as 0.6v, the reference voltage of the ltc3626. at light load currents, the 1768a is capable of operating in burst mode ? , which makes for greater efficiency, and during shutdown, it consumes less than 2a of quiescent current. in continuous mode operation, the 1768a is a high efficiency circuit over 90%. the 1768a can also track another voltage with the ltc3626 l , lt, ltc, ltm, burst mode, linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. performance summary track function. because of the current and temperature monitoring and limiting capabilities of the ltc3626, the 1768a input or output current, as well as its maximum temperature can be limited or clamped. the 1768a uses low profile surface mount components, due to the high switching frequency capability of the ltc3626, which is programmable up to 3mhz. all these features make the 1768a an ideal circuit for use in industrial applications. design files for this circuit board are available at http://www.linear.com/demo parameter conditions value input voltage range 3.6v C20v output voltage range 0.6v-6v run/shutdown gnd = shutdown v in = run output voltage regulation v in = 3.6v to 20v, i out = 0a to 2.5a 1.2v 2% typ. (1.176v C 1.224v) v in = 3.6v to 20v, i out = 0a to 2.5a 1.8v 2% typ. (1.764v C 1.836v) v in = 4v to 20v, i out = 0a to 2.5a 3.3v 2% typ. (3.234v C 3.366v) typical output ripple voltage v in = 12v, v out = 1.8v i out = 2.5a (20mhz bw) < 20mv p-p burst mode-to-continuous mode transition current values v in = 12v, v out = 1.2v i out < 680ma v in = 12v, v out = 1.8v i out < 880ma v in = 12v, v out = 3.3v i out < 1.2a mode mode pin = intv cc burst mode mode = gnd fcm (forced continuous mode) mode = floating synchronized or burst mode nominal switching frequency r t = 324k 1mhz 20% r t connected to intv cc 2mhz 30%
2 dc1768af demo manual dc1768a quick start procedure demonstration circuit 1768a is easy to set up to evaluate the performance of the ltc3626. for proper measurement equipment configuration, set up the circuit according to the diagram in figure 1. before proceeding to test, check that the shunts are inserted into the default locations: 1.2v position of the output voltage header jp1, the ss posi- tion of the soft-start/track header jp5, the fcm (forced continuous mode) position of the mode header jp6, the on position of run header jp7, the 1mhz position of the frequency header jp8, the ext position of the i th header jp9, the set/off position of the temperature set header jp10, the off position of the temp. monitoring header jp11, the off position of the output current monitoring header jp12, and the off position of the input current monitoring header jp13. when measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscillo- scope 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 2 for proper scope probe measurement technique. with the 1768a set up according to the proper measure- ment configuration and equipment in figure 1, apply 6.3v at v in (do not hot-plug v in or increase v in over the rated maximum supply voltage of 20v, or the part may be dam- aged.). measure v out ; it should read 1.2v (if desired, the quiescent current of the circuit can be monitored now by swapping the shunt in header jp7 into the off position.). the output voltage should be regulating. measure v out it should measure 1.2v 1% (1.188v to 1.212v). vary the input voltage from 3.6v to 20v and adjust the load current from 0 to 2.5a. v out should regulate around 1.2v 2% (1.176v to 1.224v). measure the output ripple voltage; it should measure less than 20mvac. set the input voltage to 12v and the output current to any current less than 1.25a. observe the discontinuous mode of operation at the switch node, and measure the output ripple voltage. it should measure less than 50mv. change the shunt position on the mode header from bm to fcm (forced continuous mode) and observe the voltage waveform at the switch pins (the other side of the inductor from the output). verify the switching frequency is between 850khz and 1.2mhz (t = 1.17s and 833ns), and that the switch node waveform is rectangular in shape. insert the jp7 shunt into the off position and move the shunt in the 1.2v output jp1 header into any of the two remaining output voltage option headers: 1.8v (jp2) or 3.3v (jp3). just as in the 1.2v v out test, the output volt- age should read v out 1% tolerance under static line and load conditions and 1% tolerance under dynamic line and load conditions 2% total). also, the circuit operation in discontinuous mode will be the same. monitor the input and output currents, and the die tem- perature, by changing the shunts on headers jp13, jp12, and jp11, respectively. the currents and temperature can even be limited using headers jp13, jp12, and jp10 C the tset header, and adjusting the values of resistors r12, r13, and r14 (consult the input/output current and on- die temperature monitor and limit section of the ltc3626 datasheets for more details.). when finished, turn off the circuit by inserting the shunt in header jp7 into the off position. 3 dc1768af demo manual dc1768a quick start procedure table 1. jumper description jumper function range/setting (default) jp1 output voltage setting. 1.2v jp5 soft-start (track or ss) track C (ss) jp6 mode/sync: forced continuous mode (fcm), burst mode, or sync (fcm) C bm C sync jp7 run (on) C off jp8 frequency (freq) (1mhz) C 2mhz jp9 ith: external comp. (ext) or internal (intv cc ) comp. (int) (ext) C int jp10 temperature setting (tset): externally set (ext set) or internally set (intv cc ) or off (set/off) ext set C (set/off) jp11 temperature monitoring (tmon) on C (off) jp12 output current monitoring (i out ) on C (off) jp13 input current monitoring (i in ) on C (off) 4 dc1768af demo manual dc1768a quick start procedure figure 1. proper equipment measurement set-up figure 2. measuring input or output ripple + C i out load + C + C + C i in v s v in + C v out + C gnd vin 5 dc1768af demo manual dc1768a figure 3. switch node voltage, output ripple voltage & inductor ripple current waveforms v in = 12v, v out = 3.3v, i out = 2.5a, f sw = 1mhz trace 1: switch voltage (10v/div) trace 2: output ripple voltage (20mv/div ac) trace 4: inductor ripple current (2a/div) figure 4. load step response v in = 12v. v out = 1.2v, 2.5a load step (0a-2.5a) forced continuous mode, f sw = 1mhz. trace 2: output voltage (20mv/div ac) trace 4: output current (1a/div) normal switching frequency and output ripple voltage waveforms load step response waveforms quick start procedure 6 dc1768af demo manual dc1768a figure 5. load step response v in = 12v, v out = 1.8v, 2.5a load step (0a-2.5a) forced continuous mode f sw = 1mhz trace 2: output voltage (50mv/div ac) trace 4: output current (1a/div) figure 6. load step response v in = 12v, v out = 3.3v, 2.5a load step (0a-2.5a) forced continuous mode f sw = 1mhz trace 2: output voltage (50mv/div ac) trace 4: output current (1a/div) load step response waveforms load step response waveforms quick start procedure 7 dc1768af demo manual dc1768a 20 35 50 65 80 95 1.00e-03 1.00e-02 1.00e-01 1.00e+00 1.00e+01 efficiency (%) load current (a) vo = 3.3v vo = 1.8v vo = 1.2v with a current sense resistor of 4.02k connected to both the input and output current monitors, their voltages equate to: v ioutmon = 2a/16000 4.02k = 0.503v v inmon = 620ma/16000 4.02k = 0.156v figure 8. efficiency graph v in = 12v, burst mode, f sw = 1mhz l:1 h vishay ihlp-2020bz-er-1r0-mo1 quick start procedure figure 7. input and output current monitoring v in = 12v, i in = 620ma, v out = 3.3v, i out = 2a, f sw = 1mhz trace 1: i outmon voltage (0.5v/div) trace 2: i inmon voltage (0.1v/div) trace 3: i out current (2a/div) trace 4: i in current (500ma/div) 8 dc1768af demo manual dc1768a parts list item qty reference part description manufacturer/part number required circuit components 11c ith cap., np0, 220pf, 25v, 10%, 0402 avx, 04023a221kat2a 2 1 c1 cap., x5r, 2.2f, 16v, 20%, 0603 tdk, c1608x5r1c225m 3 2 c3, c6 cap., x7r, 22f, 25v, 20%, 1210 murata, grm32er71e226m 4 1 c4 cap., x5r, 47f, 6.3v, 20%, 1206 taiyo yuden, jmk316bj476ml-t 5 1 c5 cap., np0, 22pf, 50v, 10% 0402 avx, 04025a220kat 6 1 c8 cap., x7r, 0.1f, 25v, 10% 0603 tdk, c1608x7r1e104k 7 1 c11 cap., x5r, 1f, 6.3v, 10% 0402 avx, 04026d105kat2a 8 1 l1 inductor, 1.0h ihlp-2020bz-01 vishay ihlp-2020bzer1r0m01 9 1 rith res., chip, 13k, 0.06w, 5% 0402 vishay, crcw040213k0jned 10 2 r3, r4 res., chip, 115k, 0.06w, 1% 0402 vishay, crcw0402115kfked 11 1 u1 ic. LTC3626EUDC, 3 4mm, 20 qfn linear tech., LTC3626EUDC#pbf additional demo board circuit components 12 0 cc(opt) cap., 0402 13 1 c2 cap., tant. 3.3f, 35v, 20%, 6032 avx, tajw335m035r 14 0 c7, c10(opt) cap., 1206 15 1 c9 cap., x7r, 2200pf, 25v, 20%, 0402 avx, 04023c225mat 16 2 c12, c13 cap., x5r, 1f, 25v, 10%, 0603 tdk, c1608x5r1e105k 17 0 c14(opt) cap., 1812 18 1 c15 cap., x5r, 0.33f, 25v, 20%, 0603 avx, 06033d334mat 19 0 d1(opt) schottky diode, sod-323 20 2 r10, r on res., chip, 0, 0.06w, 0402 vishay, crcw04020000z0ed 21 1 r1 res., chip, 100k, 0.06w, 5%, 0402 vishay, crcw0402100kfked 22 1 r2 res., chip, 324k, 0.06w, 1%, 0402 nic, nrc04f3243trf 23 1 r5 res., chip, 57.6k, 0.06w, 1%, 0402 vishay, crcw040257k6fked 24 1 r6 res., chip, 25.5k, 0.06w, 1%, 0402 vishay, crcw040225k5fked 25 0 r7, r9, r14(opt) res., 0402 26 2 r8, r11 res., chip, 1m, 0.06w, 5%, 0402 vishay, crcw04021m00jned 27 2 r12, r13 res., chip, 4.02k, 0.06w, 1%, 0402 vishay, crcw04024k02fked 28 1 r17 res., chip,10, 0.06w, 5%, 0402 vishay, crcw040210r0jned hardware: for demo board only 29 13 e1-e13 turret,testpoint mill max2501-2-00-80-00-00-07-0 30 4 jp1, jp2, jp3, jp4 2 pin 0.079 single row header samtec, tmm102-02-l-s 31 1 jp5 2x2, 0.079 double row header samtec, tmm102-02-l-d 32 1 jp6 2x3, 0.079 double row header samtec, tmm103-02-l-d 33 7 jp7-jp13 3 pin 0.079 single row header samtec, tmm103-02-l-s 34 10 xjp1, xjp5-xjpp13 shunt, .079" center samtec, 2sn-bk-g 35 4 mh1-mh4 stand-off, nylon 0.25" keystone, 8831(snap on) 9 dc1768af demo manual dc1768a 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. schematic diagram 5 5 4 4 3 3 2 2 1 1 d d c c b b a a & |