1 dc1666af demo manual dc1666a description LT3791 four-switch buck-boost led driver controller demonstration circuit dc1666a is a synchronous four- switch buck-boost led driver controller. it accepts an input voltage from 4.7v to 60v, and drives up to 25v of leds at 2a. dc1666a features both pwm and analog dimming of the led string. it has an openled flag that indicates when the led string has been removed and it has a shortled flag that indicates that the output has been shorted to gnd. in both cases, the ic remains in control and well protected. dc1666a features very high efficiency at 300khz switching frequency and continuous conduction mode (c cm ). the synchronous four-switch topology both steps up and steps down voltage while regulating up to 50w of constant led output current at efficiencies up to 98%. the circuit can be altered for applications requiring over 100w of leds. an optional sync terminal is provided for synchronizing to an external clock and clkout terminal provides a source to sync another converter to the internal clock of the lt ? 3791. three sense resistors provide constant output current control and monitoring, peak switch current control, and dc input current limit and monitoring. the i smon and i vinmon outputs tell the user how much current is flowing through the output and input sense resistors. small ceramic input and output capacitors are used to save space and cost. the open led overvoltage protection uses the ics constant voltage regulation loop to limit the output to approximately 28.3v if the led string is opened. for low input voltage operation, the ctrl pin voltage is reduced as the input voltage drops below 6.5v, reducing led brightness and restraining the peak switch currents in order to limit inductor and switch size. uvlo turns the leds off when v in drops below 4.7v. when input rises above 57.6v, overvoltage lockout turns the switches off to protect them and they turn back on when v in drops below 56.2v. dc1666a pwm dimming is simple. the pwm dimming mosfet turns the led string on and off with an input to the pwm dimming terminal. for the highest pwm dimming ratio, it is recommended to use 100hz as a pwm dimming frequency. information regarding pwm dimming ratios and performance can be found in the applications information section of the LT3791 data sheet. analog dimming is also simple with a simple voltage source on the ctrl terminal. modifications can be made to dc1666a in order to convert the board to higher or lower power or from an led driver to a constant voltage regulator or battery charger. please consult the factory or the LT3791 data sheet for details. the LT3791 data sheet gives a complete description of the part, operation and applications information. the data sheet must be read in conjunction with this demo manual for demonstration circuit dc1666a. the LT3791 is assembled in a 38-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 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.
2 dc1666af demo manual dc1666a p erformance s ummary (t a = 25c) parameter condition value (typical) input voltage pv in range* operating 4.7v to 60v* switching frequency r12 = 86.6k 300khz i led ctrl = float, 7v < pv in < 57.6v 2.0a v led range r7 = 1m, r9 = 44.2k 9.5v < v led < 25.5v open led voltage r7 = 1m, r9 = 44.2k 28.3v typical efficiency boost region pvin = 20v, v led = 25v, i led = 2a 97.5% typical efficiency buck-boost region pvin = 24v, v led = 25v, i led = 2a 96.8% typical efficiency buck region pvin = 30v, v led =25v, i led = 2a 97.3% undervoltage lockout (falling turn-off) r13 = 332k and r6 = 115k 4.7v undervoltage lockout (rising turn-on) r13 = 332k and r6 = 115k 5.7v overvoltage lockout (rising turn-off) r11 = 54.9k, r19 = 1m 57.6v overvoltage lockout (falling turn-on) r11 = 54.9k, r19 = 1m 56.2v peak switch current limit boost region rs = 0.004 11a valley switch current limit buck region rs = 0.004 10a * the guaranteed input voltage range of the LT3791 is 4.7v to 60v. overvoltage lockout is set externally at 57.6v on this demo circuit to protect the 60v mosfets m1 and m2. overvoltage lockout is adjustable.
3 dc1666af demo manual dc1666a demonstration circuit dc1666a is easy to set up to evaluate the performance of the LT3791. follow the procedure below: note: pwm must be pulled high to run. if pwm is not used, connect pwm to a 5v source or to intv cc on the pcb using 0 resistor r22. 1. connect a string of leds that will run with forward volt - age less than 25.5v, but greater than 9.5v, to the led + and led C terminals on the pcb as shown in figure 1. 2. connect the en/uvlo terminal to gnd. 3. with power off, connect the input power supply to the pvin and gnd terminals. make sure that the pvin dc input voltage will not exceed 60v. 4. connect the pwm terminal. if pwm is not used, connect pwm to a 5v source or to intv cc on the pcb using 0 resistor r22. pwm must be pulled high to run. 5. turn the input power supply on and make sure the voltage is between 4.7v and 60v . 6. release the en/uvlo to gnd connection. 7. observe the led string running at the programmed led current. 8. for pwm dimming, connect a p wm (100hz or higher is recommended) signal to the pwm terminal. for analog dimming, connect a dc voltage between 0v and 2v to the ctrl terminal. 9. observe the reduction of brightness in the led string when p wm or analog dimming. quick s tart p roce d ure
4 dc1666af demo manual dc1666a q uick start proce d ure figure 1. test procedure setup drawing for dc1666a
5 dc1666af demo manual dc1666a q uick start proce d ure figure 2. dc1666a efficiency with 25v leds at 2a figure 3. dc1666a 100hz 50:1 pwm dimming waveforms at 12v in and 25v led at 2a input voltage (v) 0 80 efficiency (%) 84 88 92 10 20 30 40 3791 ta02b 50 96 100 82 86 90 94 98 60 buck boost buck-boost pwm 5v/div i l1 2a/div i led 2a/div 50s/div 3791 ta02c figure 4. dc1666a ctrl led current foldback at low v in with uvlo falling and rising and ovlo input voltage (v) uvlo (falling) turn-on (rising) 3 0 i led (a) 4 5 6 7 dc1666a f04 8 1.0 2.0 0.5 1.5 9 10 50 55 60 turn-on (falling) ovlo (rising)
6 dc1666af demo manual dc1666a p arts list item qty reference part description manufacturer/part number required electrical components 1 1 c ss cap x7r 0.01f 50v 10% 0603 avx, 06035c103kat2a 2 1 c c cap x7r 0.022f 50v 10% 0603 avx, 06035c223kat2a 5% 3 4 c2, c3, c12, c14 cap x7r 2.2f 100v 10% 1210 avx, 12101c225kat2a 4 1 c5 cap x7r 1f 100v 10% 1206 avx, 12061c105kat2a 5 3 c6, c8, c11 cap x5r 0.1f 16v 10% 0402 avx, 0402yd104kat2a 6 1 c7 cap x5r 4.7f 10v 10% 0603 avx, 0603zd475kat2a 7 4 c9, c10, c13, c15 cap x7r 4.7f 50v 10% 1210 avx, 12105c475kat2a 8 2 d1-d2 diode single schottky barrier diode sod-323 nxp, bat46wj 9 1 l1 inductor 10h cooper bussmann, hc9-100-r 10 2 m1, m2 mosfet n-channel 60v lfpak renesas, rjk0651dpb-00-j5 11 2 m3, m4 mosfet n-channel 40v lfpak renesas, rjk0451dpb-00-j5 12 1 m5 mosfet n-channel 40v sot-23 vishay, si2318ds-t1-e3 13 1 r led res chip 0.050? 1% 2010 vishay, wsl2010r0500fea 14 1 r s res chip 0.004? 1w 1% 2010 vishay, wsl20104l000fea 15 1 r7 res chip 1m 1% 0402 vishay, crcw04021m00fked 16 1 r9 res chip 44.2k 1% 0402 vishay, crcw040244k2fked 17 1 r12 res chip 86.6k 1% 0402 vishay, crcw040286k6fked 18 1 u1 ic LT3791efe 38-lead tssop version aa tssop linear, LT3791efe#pbf optional electrical components 1 1 c4 cap x5r 0.47f 6.3v 10% 0402 avx, 04026d474kat2a 2 0 c16, c17 cap 1210 optional 3 0 c18 cap 0603 optional 4 0 d3, d4 diode smb optional 5 2 r c , r16 res chip 0? 0402 vishay, crcw04020000z0ed 6 1 r in res chip 0.003? 1w 1% 1206 irc, ulr-g-1-1206-r003-1-lf-slt 7 1 r2 res chip 0? 1206 vishay, crcw12060000z0ea 8 1 r3 res chip 1m 1% 0402 vishay, crcw04021m00fked 9 2 r4, r5 res chip 200k 5% 0603 vishay, crcw0603200kjnea 10 1 r6 res chip 115k 1% 0603 vishay, crcw0603115kfkea 11 1 r8 res chip 237k 1% 0402 vishay, crcw0402237kfked 12 0 r10, r15, r18, r20, r21 res chip 0402? 0402 optional 13 1 r11 res chip 54.9k 1% 0402 vishay, crcw040254k9fked 14 1 r13 res chip 332k 1% 0402 vishay, crcw0402332kfked 15 1 r14 res chip 0? 0603 vishay, crcw06030000z0ea 16 1 r17 res chip 51? 5% 0402 vishay, crcw040251r0jned 17 1 r19 res chip 1m 1% 0603 vishay, crcw06031m00fked 18 0 r22, r23 res chip 0? 0603 optional hardware 1 22 e1-e22 turret 0.095 mill-max, 2501-2-00-80-00-00-07-0
7 dc1666af demo manual dc1666a 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 ivinmon vin 4.7v - 60v pvin 4.7v - 60v 100v 100v shortled openled 10v led- gnd led+ out ismon clkout ovlo ctrl en/uvlo 100v 1206 1210 1210 hc9-100-r sumida 50v 1210 1210 50v 0603 gnd intvcc 1210 2010 1206 gnd gnd sync gnd gnd all capacitors are 0603. note: unless otherwise specified bat46wj bat46wj 2010 pwm 300khz all resistors are 0402. 2a 100v 100v openled pvin intvcc intvcc openled intvcc vref vref r2 0 r2 0 m2 rjk0651dpb m2 rjk0651dpb c17 (opt) c17 (opt) c18 opt c18 opt rc 0 rc 0 e12 e12 c15 4.7uf 50v 1210 c15 4.7uf 50v 1210 m3 rjk0451dpb m3 rjk0451dpb c14 2.2uf 1210 c14 2.2uf 1210 d3 opt d3 opt e2 e2 r8 237k r8 237k r6 115k 0603 r6 115k 0603 r17 51 r17 51 r7 1m r7 1m r12 86.6k r12 86.6k e8 e8 c2 2.2uf c2 2.2uf m5 si2318ds m5 si2318ds rin 0.003 rin 0.003 e11 e11 m4 rjk0451dpb m4 rjk0451dpb c12 2.2uf 1210 c12 2.2uf 1210 e3 e3 e14 e14 c9 4.7uf c9 4.7uf r14 0 0603 r14 0 0603 e21 e21 r22 opt 0603 r22 opt 0603 r19 1m r19 1m r18 opt r18 opt d1 d1 e7 e7 l1 10uh l1 10uh m1 rjk0651dpb m1 rjk0651dpb c8 0.1uf 0402 c8 0.1uf 0402 r21 opt r21 opt u1 LT3791efe u1 LT3791efe en/uvlo 9 shortled 5 openled 4 ivinn 11 ctrl 1 pwm 3 isp 25 sync 34 ss 2 pwmout 31 vc 36 rt 35 test2 32 ivinmon 8 ismon 7 ivinp 10 clkout 33 vref 6 ovlo 38 snsn 28 snsp 27 isn 26 pgnd 17 pgnd 20 fb 37 tg2 24 sw2 21 bg2 19 bg1 18 sw1 16 tg1 14 bst1 15 bst2 22 nc 23 vin 12 intvcc 13 sgnd 30 pgnd 39 test1 29 c3 2.2uf c3 2.2uf cc 22nf cc 22nf c16 (opt) c16 (opt) c4 470nf 0402 c4 470nf 0402 c11 0.1uf 0402 c11 0.1uf 0402 d4 opt d4 opt e13 e13 r11 54.9k r11 54.9k r20 opt r20 opt e15 e15 c7 4.7uf c7 4.7uf r5 200k 0603 r5 200k 0603 r15 opt r15 opt m6 opt m6 opt c13 4.7uf 50v 1210 c13 4.7uf 50v 1210 r4 200k 0603 r4 200k 0603 c5 1uf c5 1uf css 10nf css 10nf e10 e10 e17 e17 d2 d2 e20 e20 rled 0.05 rled 0.05 e22 e22 r13 332k r13 332k e5 e5 e6 e6 r10 opt r10 opt c10 4.7uf c10 4.7uf r16 0 r16 0 e18 e18 r9 44.2k r9 44.2k r23 opt 0603 r23 opt 0603 rs 0.004 rs 0.004 c6 0.1uf 0402 c6 0.1uf 0402 e16 e16 e4 e4 e1 e1 e9 e9 r3 1m r3 1m e19 e19
8 dc1666af demo manual dc1666a linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com ? linear technology corporation 2012 lt 0312 ? 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 applica- tion engineer. mailing address: linear technology 1630 mccarthy blvd. milpitas, ca 95035 copyright ? 2004, linear technology corporation
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