1 dc2079af demo manual dc2079a description lt 3954 40v in 40v out led driver demonstration circuit 2079 a is a 40v in , 40v out led driver. it generates its own pwmout waveform from its internal pwm generator for accurate pwm dimming with up to 33:1 brightness ratio. it accepts an input voltage from 5v to 30 v and drives up to 32 v of leds at 650ma (when pv in is less than v led ). dc2079a features both pwm and analog dimming of the led string. it has an openled flag that indicates when the led string has been removed. dc2079a features high efficiency at 350 khz switching frequency. at high led string voltages up to 32 v and 650ma of led current, the single switch controller has 94.6% efficiency (14 v input). the LT3954 has an internal 40v, 5.4 a switch that simplifies the schematic and layout. 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 regulate the output to approximately 35 v if the led string is opened although it may reach 38 v peak during transient from running leds to open string. for low input voltage operation, the ctrl pin voltage is reduced as the input voltage drops below 8.5 v, 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 5.3v. dc2079a pwm dimming is simplified when compared with other led drivers. the LT3954 generates its own pwmout dimming waveform at a frequency determined by the capacitance on the pwm pin ( c16 gives 300 hz for dc2079a). the pwmout duty cycle is determined by the voltage on the dim terminal. between 0 v and 8 v vdim gives between 3% and 97% pwm duty cycle. information regarding pwm dimming ratios and performance can be found in the LT3954 data sheet in the applications sec- tion. analog dimming is also simple to use with a single voltage source on the ctrl terminal. modifications can be made to dc2079a in order to convert the board to power different led strings or from an led driver to a constant voltage regulator or battery charger. it can easily be changed from a boost topology to a sepic, buck mode, or buck- boost mode led driver. please consult the factory or the LT3954 data sheet for details. it can be modified to provide led+ to gnd short-circuit protection as well. the LT3954 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 dc2079a. the LT3954euhe is assembled in a 36- lead plastic qfn package with two thermal pads underneath the ic . 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 dc2079af demo manual dc2079a p erformance s ummary specifications are at t a = 25c parameter condition value (typical) input voltage pvin range operating 5v to v led (up to 40v) switching frequency r1 = 28.7k 350khz i led rs1 = 0.39 8.4v < pvin < v led (40v) 645ma low pvin i led (ctrl foldback) rs1 = 0.39, pvin = 6.0v rs1 = 0.39 , pvin = 7.0v rs1 = 0.39, pvin = 8.0v 486ma 577ma 640ma v led range r7 = 1m, r8 = 37.4k pv in < v led < 32v open led voltage r7 = 1m, r8 = 37.4k 34.8v typical efficiency pv in =14v, v led = 32v, i led = 645ma pwm = intv cc 94.6% pvin undervoltage lockout (falling turn-off) r3 = 499k and r4 = 147k 5.3v pvin undervoltage lockout (rising turn-on) r3 = 499k and r4 = 147k 6.5v intv cc operating 7.85v peak switch current limit 5.4a pwmout dimming duty cycle v dim = 8.0v v dim = 4.0v v dim = 1.5v v dim = 0v 97.5% 50% 10% 3.1% internal pwm dimming frequency c16 = 0.047f, 0v < v dim < 8v 300hz
3 dc2079af demo manual dc2079a demonstration circuit dc2079a is easy to set up to evalu- ate the performance of the LT3954. follow the procedure below: 1. connect a string of leds that will run with forward voltage less than or equal to 32 v, but greater than the intended pvin, to the led+ and ledC 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 pv in and gnd terminals. make sure that the pv in dc input voltage will not exceed 40v (or v led ). 4. connect the dim terminal to a voltage between 0 v and 8v to set the internal pwmout dimming duty cycle. if this terminal is left floating the converter will run with approximately 12% pwmout dimming duty cycle. pull the pwm terminal high to intv cc to set the converter at 100% duty cycle. 5. turn the input power supply on and make sure the voltage is between 6.5v and 40v (or v led ) to start. 6. release the en/uvlo-to-gnd connection. 7. observe the led string running at the pro-grammed led current and brightness related to the programmed pwmout duty cycle. 8. to change the brightness with pw m dimming, simply vary the v dim voltage between 0 v and 8 v with the pwm terminal floating. 9. to change the brightness with analog dimming, sim- ply attach a voltage source on the ctrl terminal and reduce the voltage below 1.2v. 10. observe the reduction of brightness in the led string when pwm or analog dimming. quick s tart p roce d ure
4 dc2079af demo manual dc2079a figure 1. test procedure setup drawing for dc2079a quick s tart p roce d ure
5 dc2079af demo manual dc2079a quick s tart p roce d ure figure 2. dc2079a efficiency with 32v leds at 650ma and 100% pwmout duty cycle figure 3. dc2079a 300hz pwm dimming waveforms at different pwmout duty cycles figure 4. dc2079a ctrl led current foldback at low pv in with uvlo (falling and rising) pv in (v) 4 i led (a) 0.7 0.5 0.4 0.2 0.3 0.6 0.1 0 8 5 dc2079a f04 12 76 11109 under voltage lockout (falling) turn-on (rising) pv in (v) 5 efficiency (%) 100 90 96 98 88 84 86 94 92 82 80 25 10 dc2079a f02 30 20 15 32v led 650ma pwm = intv cc dc2079a f03 i led 500ma/div v in = 12v v led = 32v v dim = 8v dc pwm = 97.5% v dim = 3.9v dc pwm = 47% v dim = 1.5v dc pwm = 10% v dim = 0v dc pwm = 3.1%
6 dc2079af demo manual dc2079a p arts list item qty reference part description manufacturer/ part number required circuit components 1 1 c1 cap., x5r 1f 50v 20% 1206 tdk c3216x5r1h105m 2 1 c2 cap., x5r 10f 50v 20% 1210 taiyo yuden umk325bj106mm-t 3 2 c4, c5 cap., x5r 4.7f 50v 20% 1210 taiyo yuden umk325bj475mm-t 4 1 c9 cap., x7r 4.7nf 25v 20% 0603 avx 06033c472 mat 2a 5 1 c10 cap., x7r 0.01f 25v 10% 0603 avx 06033c103 kat 2a 6 1 c11 cap., x7r 1f 10v 10% 0603 taiyo yuden lmk107bj105ka 7 1 c16 cap., x7r 47nf 16v 20% 0603 taiyo yuden emk107bj473ma 8 1 d1 schottky diode 5a powerdi5 diodes inc. pds560-13 9 1 l1 inductor, 22h cooper coiltronics dr125-220 10 1 m1 mosfet n-chan., 40v sot23 siliconix si2318cds-t1-ge3 11 1 rs1 res., chip 0.39, 0.25w 1% 1206 panasonic erj-8rqfr39v 12 1 r1 res., chip 28.7k 0.06w 1% 0402 vishay crcw040228k7fked 13 1 r2 res., chip 5.1k 0.06w 5% 0402 vishay crcw04025k10jned 14 1 r7 res., chip 1.00m 0.06w 1% 0603 vishay crcw06031m00fkea 15 1 r8 res., chip 37.4k 0.06w 1% 0402 vishay crcw040237k4fked 16 1 r21 res., chip 124k 0.06w 1% 0603 vishay crcw0603124kfkea 17 1 u1 i.c.,40vin/ 40vout led driver linear tech. corp. LT3954euhe optional circuit components 1 1 c3 cap., x5r 10f 50 v 20% 1210 t aiyo y uden umk325bj106mm-t 2 0 c6-c8, c12-c15 cap., 1210 optional 3 0 c17 cap., 0603 optional 4 0 q1 diode, sot23 optional 5 1 r3 res., chip 499k 0.06w 1% 0603 vishay crcw0603499kfkea 6 1 r4 res., chip 147k 0.06w 1% 0603 vishay crcw0603147kfkea 7 1 r5 res., chip 1m 0.06w 1% 0402 vishay crcw04021m00fked 8 1 r6 res., chip 165k 0.06w 1% 0402 vishay crcw0402165kfked 9 1 r9 res., chip 100k 0.06w 5% 0603 vishay crcw0603100kjnea 10 0 r10 res., 0805 optional 11 1 r11 res., chip 0? 0.33w 6a 0805 vishay crcw08050000zoea 12 1 r12 res., chip 0? 0.5w 10a 1206 vishay crcw12060000zoea 13 0 r13, r14, r16, r19, r20, r23 res., 0603 optional 14 0 r15 res., 1206 optional 15 0 r17, r18, r22 res., 0402 optional 16 1 r24 res., chip 0? 0.25w 5a 0603 vishay crcw06030000z0ea hardware 1 9 e1-e5, e7, e8, e12, e13 turret, testpoint mill max 2501-2-00-80-00-00-07-0 2 7 e6, e9-e11, e14-e16 turret, testpoint mill max 2308-2-00-80-00-00-07-0
7 dc2079af demo manual dc2079a 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 * see demo manual for input range 1206 notes: unless otherwise specified. 1. resistors are 0402 case size. 2. capacitors are 0603 case size. -vmode pvin out sync sync pvin sync intvcc out intvcc out out out intvcc r10 (opt) 0805 r10 (opt) 0805 c10 0.01f c10 0.01f r17 (opt) r17 (opt) r4 147k 1% 0603 r4 147k 1% 0603 c14 (opt) 1210 c14 (opt) 1210 r11 0 ohm 0805 r11 0 ohm 0805 e1 pvin 5v - 30v* e1 pvin 5v - 30v* c2 10f 50v 1210 c2 10f 50v 1210 e6 ctrl e6 ctrl r1 28.7k 1% 350khz r1 28.7k 1% 350khz r5 1m r5 1m l1 22h dr125-220 l1 22h dr125-220 r3 499k 0603 r3 499k 0603 e5 out e5 out c15 (opt) 1210 c15 (opt) 1210 r21 124k 1% 0603 r21 124k 1% 0603 c16 47nf 300hz c16 47nf 300hz c4 4.7f 50v 1210 c4 4.7f 50v 1210 q1 (opt) q1 (opt) c6 (opt) 1210 c6 (opt) 1210 c1 1f 50v 1206 c1 1f 50v 1206 r13 (opt) 0603 r13 (opt) 0603 u1 LT3954euhe u1 LT3954euhe vref 32 pgnd 17 isp 28 isn 27 pgnd 14 vc 30 intvcc 3 pgnd 16 dim/ss 35 pwm 33 vmode 34 pgnd 15 pwmout 23 fb 25 sw 38 vin 6 en/uvlo 2 ctrl 31 rt 36 gnd 37 sw 21 pgnd 13 gndk 12 gnd 4 gnd 24 sync 1 sw 8 sw 9 nc 10 sw 20 r12 0 ohm r12 0 ohm e3 pgnd e3 pgnd r23 (opt) 0603 r23 (opt) 0603 r20 (opt) 0603 r20 (opt) 0603 r22 (opt) r22 (opt) e2 vin 5v - 30v* e2 vin 5v - 30v* c12 (opt) 1210 c12 (opt) 1210 e9 pwm e9 pwm e14 sync e14 sync c11 1f 10v c11 1f 10v e12 gnd e12 gnd e13 gnd e13 gnd r24 0 ohm 0603 r24 0 ohm 0603 e15 dim e15 dim e11 vmode e11 vmode e16 intvcc e16 intvcc r6 165k 1% r6 165k 1% e10 en/uvlo e10 en/uvlo r2 5.1k r2 5.1k r7 1.00m 1% 0603 r7 1.00m 1% 0603 e8 led- e8 led- c17 (opt) c17 (opt) e7 led+ 32v led max 650ma e7 led+ 32v led max 650ma c3 10f 50v 1210 c3 10f 50v 1210 c8 (opt) 1210 c8 (opt) 1210 m1 si2318ds m1 si2318ds c9 4.7nf c9 4.7nf e4 pgnd e4 pgnd r15 (opt) 1206 r15 (opt) 1206 c5 4.7f 50v 1210 c5 4.7f 50v 1210 r8 37.4k 1% r8 37.4k 1% d1 pds560-13 d1 pds560-13 r9 100k 0603 r9 100k 0603 r19 (opt) 0603 r19 (opt) 0603 r18 (opt) r18 (opt) rs1 0.39 1% 1206 rs1 0.39 1% 1206 r14 (opt) 0603 r14 (opt) 0603 c13 (opt) 1210 c13 (opt) 1210 c7 (opt) 1210 c7 (opt) 1210 r16 (opt) 0603 r16 (opt) 0603
8 dc2079af demo manual dc2079a linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com ? linear technology corporation 2013 lt 0413 ? 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
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