1 description lt 3797eukg triple led boost controller dc1784a is a triple boost led driver featuring the lt3797 triple boost led controller. it accepts an input voltage from 2.5 v to 40v ( with higher transient) and drives three independent strings of up to 50 v leds at 1 a. dc1784a features independent pwm and analog dimming of each of the three led strings. each of the three channels has its own short-circuit protection, open led protection, and fault flag output. each or every channel can be altered to run as a different topology such as buck-boost mode, buck mode, or sepic depending upon the relationship between input and output voltage. although the boost is set up to power 50 v of leds at 1 a, the maximum led string voltage can be changed to almost 100 v and the led current can be adjusted by merely changing a few resistors and external components. dc1784a features high efficiency at 310 khz switching frequency. at high led string voltages up to 50 v and 1a of led current, the triple led boost controller has 93.5% efficiency. the switching frequency can be adjusted be - tween 100 khz and 1 mhz with a single resistor. all three channels run in-phase with each other and an external sync pin can be used to set the switching frequency and phasing, as well as to optimize pwm dimming. for low input voltage operation, down to 2.5v, the ctrl pin voltage is reduced as the input voltage drops below 10.5v, reducing led brightness and restraining the peak switch currents in order to limit thermal rise on this pcb. the lt3797 has a unique, internal buck-boost intv cc supply that powers the gate drivers at 7.8 v, regardless of the state of the input voltage, rather than using an ldo from the input. uvlo turns the leds off when v in drops below 2.5 v. internal ovlo turns off the switching when 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. the input exceeds 41 v, but ovlo can be programmed externally to a lower voltage if desired. the lt3797 can withstand transients up to 60 v. dc1784a can withstand transients up to 50v with c3 > 50v rating. 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 55 v if the led string is opened although it may reach 59 v peak during transient from running leds to open. the unique fbh ( feedback high) pins allow the overvoltage protection of non-grounded led driver topologies such as buck-boost mode and buck mode to be accomplished with just two resistors. modifications can be made to dc1784a in order to convert the independent channels to higher or lower power or from led drivers to constant voltage regulators. they can easily be changed from boost topology to sepic, buck mode, or buck-boost mode led drivers. please consult the factory or the lt3797 data sheet for details. the lt3797 data sheet gives a complete description of the device, operation and applications information. the data sheet must be read in conjunction with this demo manual for dc1784a. the LT3797EUKG is assembled in a 52-lead (7mm 8 mm) plastic qfn ukg package with a thermally enhanced ground pad. proper board layout is essential for maximum thermal performance. see the data sheet section layout considerations. design files for this circuit board are available at http://www . linear.com/demo/dc1784a dc1784af demo manual dc1784a
2 quick s tart p roce d ure dc1784a is easy to set up to evaluate the performance of the LT3797EUKG. follow the procedure below: 1. connect three strings of leds that will run with forward voltage less than 50 v (at 1 a), but greater than pvin, to the led + and gnd 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 does not exceed 40v (or v led ). 4. turn the input power supply on and make sure the voltage is between 2.5v and 40v (or v led ). 5. connect the pwm 1-3 input terminals to intv cc or v ref to enable 100% brightness control when en/uvlo is released. 6. release the en/uvlo-to-gnd connection. 7. observe the led strings running at the programmed led current. 8. to change the brightness with analog dimming, sim - ply attach a voltage source on any or all of the ctrl terminals and set the voltage(s) between 0 v and 1.5v. see data sheet for details. 9. to change brightness with pwm dimming, remove the connection from pwm 1-3 to intv cc or v ref and attach a 3.3 v to 5 v rectangular waveform with varying duty cycle. p erformance s ummary parameter conditions value (typical) input voltage pvin range operating v in = pvin 2.5v to v led (up to 40v) switching frequency r1 = 47.5k 310khz i led ch1, ch2, ch3 r2, r3, r4 = 0.25 10.5v < pvin < v led (40v) 1.0a low pvin i led (ctrl foldback) r2, r3, r4 = 0.25 pvin = 4.0v r2, r3, r4 = 0.25 pvin = 6.0v r2, r3, r4 = 0.25 pvin = 9.0v 280 ma 525ma 890ma v led range ch1, ch2, ch3 r8, r9, r10 = 23.2k r14, r15, r16 = 1m pvin < v led < 50v open led voltage ch1, ch2, ch3 r8, r9, r10 = 23.2k r14, r15, r16 = 1m 55v typical efficiency (100% pwm duty cycle) pvin = 14v v led = 50v and i led = 1a ch1, ch2, ch3 93.5% pvin under voltage lockout (falling turn-off) r26 = 100k and r27 = 105k 2.5v pvin under voltage lockout (rising turn-on) r26 = 100k and r27 = 105k 2.6v intv cc operating 7.5v peak switch current limit ch1, ch2, ch3 r11, r12, r13 = 0.008 12.5a dc1784af demo manual dc1784a
3 d e mo circuit o ptions dc1784a can be adjusted for higher output voltage, dif- ferent led current, or different topology. the following options are for simple changes to the demonstration circuit. the data sheet gives more information regarding designing with the lt3797. for more information, see the data sheet for details or contact linear technology technical support. maximum led voltage dc1784a is set for 55 v of overvoltage protection and the maximum led string voltage used on the standard build should be 50 v. however, the output can go up to 100v, so ovp can be set at about 93 v for maximum led voltage and the maximum led string voltage is therefore about 87v. the limits are based upon open led overshoot and voltage and current regulation regions. if changes are made in the fb resistors for higher voltage, the mosfet and catch diode should be switched out for higher voltage devices. see the lt3797 data sheet for details. current or voltage regulation the lt3797 can be used for constant current or voltage regulation. if the load placed on the led + to gnd terminals allows v out to climb high enough for v isp-fbh = 1.2 v, then the voltage regulation loop of the converter takes over. in this case, the compensation for a given channel should be adjusted for proper use as a constant voltage regulator. the ic can be used as a boost or sepic constant voltage regulator. output voltage can be almost as high as 100v when used as a constant voltage regulator. led current and switch current led current on dc1784a is set for 1 a with 0.25 resis - tors r 2, r3, r4. for a different maximum led current, change this resistor: 250mv/r led = i led . a change in led current or input voltage may lead to higher or lower maximum switch current. r11, r12, r13 can be changed to alter the maximum switch current for different applications. 100mv/r sense = peak switch current. overvoltage protection overvoltage protection is set with resistor pairs r 8 & r14, r9 & r15, r10 & r16. the high side feedback method allows simple changes for different topologies. for buck mode and buck-boost mode, see the data sheet for details how to set the feedback resistors. note that r35, r36, r37 are provided as optional placeholders on the demo circuit for simple feedback resistor changes for these topologies. boost, buck mode, buck-boost mode, sepic any channel of the dc 1784a can be changed to a differ- ent topology than boost. a few simple changes including feedback overvoltage protection feedback resistors, out- put resistor , components, and connection to input can be made. please consult the lt3797 data sheet and the factory for details. undervoltage and overvoltage lockout uvlo can be adjusted by changing the values of r26 and r27. the lt3797 has an internal 41 v ovlo that protects the ic from switching at high input voltage transients. however, an additional ovlo pin can be used to set a lower ovlo using resistors r28, r31, and/or r46. dc1784af demo manual dc1784a
4 d e mo circuit o ptions figure 1. test procedure setup drawing for dc1784a dc1784af demo manual dc1784a
5 figure 2. dc1784a 12v in 100hz pwm dimming waveforms at different pwm duty cycles with 250:1 in bold. i led waveform (500ma/div) is on top (with 50v led string) and il1 waveform (2a/div) is on the bottom figure 3. dc1784a ctrl led current foldback at low pvin with uvlo falling and rising figure 4. dc1784a efficiency at maximum i led vs pvin with 50v leds (at 1a) on all three channels d e mo circuit o ptions 250:1 i led i l1 0 0.2 0.4 0.6 0.8 1 0 2 4 6 8 10 12 14 i led (a) pvin (v) turn-on (rising) 30 32 34 36 38 40 42 ovlo (rising) turn-on (falling) uvlo (falling) 80 82 84 86 88 90 92 94 96 98 100 0 5 10 15 20 25 30 35 40 45 efficiency (%) pvin (v) dc1784af demo manual dc1784a
6 p arts list item qty reference part description manufacturer/ part number required circuit components 1 1 c1 cap., x7r, 1f, 50v, 10%, 0805 murata, grm21br71h105ka12l 2 6 c2, c3, c4, c31, c32, c33 cap., x7r, 4.7f, 50v, 10%, 1210 murata, grm32er71h475ka88l 3 9 c5, c6, c7, c19, c20, c21, c25, c27, c29 cap., x7s, 4.7f, 100v, 20%, 1210 tdk c3225x7s2a475m 4 4 c8, c13, c14, c15 cap., x7r, 0.1f, 10v, 10%, 0603 avx , 0603zc104 kat 2a 5 1 c9 cap., x5r, 10f, 10v, 20%, 0603 samsung cl10a106mp8nnnc 6 3 c10, c11, c12 cap., x7r, 6800pf, 25v, 10%, 0402 avx , 04023c682 kat 2a 7 3 d1, d2, d3 diode, pds360, powerdi-5 diodes/zetex, pds360-13 8 3 l1, l2, l3 ind, 10h, hc9-100-r coiltronics, hc9-100-r 9 1 l4 ind., 47h, sd series, ind-sd25 coiltronics, sd25-470-r 10 3 m1, m3, m5 mosfet, n-channel, bsc039n06ns, pwrpak so-8 infineon, bsc039n06ns 11 3 m2, m4, m6 mosfet, p-channel, si7113dn, pwrpak1212-8 vishay, si7113dn-t1-ge3 12 1 r1 res., chip, 47.5k, 1/16w, 1%, 0402 vishay, crcw040247k5fked 13 3 r2, r3, r4 res., chip, 0.25, 1w, 1%, 2010 irc, lrc-lr2010lf-01-r250-f 14 3 r5, r6, r7 res., chip, 3.9k, 1%, 0402 vishay, crcw04023k90fked 15 3 r8, r9, r10 res., chip, 23.2k, 1/16w, 1%, 0402 vishay, crcw 040223k2fked 16 3 r 11, r12, r13 res., chip, 0.008, 1w, 1%, 2010 sei, csrf2010 ft 8l00 17 3 r14, r15, r16 res., chip, 1m, 1/10w, 1%, 0603 vishay, crcw06031m00fkea 18 1 u1 ic, LT3797EUKG qfn(52)(ukg)-7mm 8mm linear tech.corp. LT3797EUKG#pbf optional electrical components 1 0 c16, c17, c18, c22, c23, c24 cap., opt 0402 opt 2 0 c26, c28, c30, c34, c35, c36 cap., opt 1210 opt 3 1 c37 cap., alum, 33f, 50v, 6.3 7.7 panasonic, eehza1h330xp 4 3 d4, d5, d6 diode, es1b, 150v/1a, sma diodes/zetex, es1b-13-f 5 3 r17, r18, r19 res., chip, 1m, 1/16w, 1%, 0402 vishay, crcw04021m00fked 6 3 r20, r21, r22 res., chip, 140k, 1/16w, 1%, 0402 vishay, crcw0402140kfked 7 3 r23, r24, r25 res., chip, 100k, 1/10w, 1%, 0603 vishay, crcw0603100kfkea 8 1 r26 res., chip, 100k, 1/16w, 1% , 0402 vishay, crcw0402100kfked 9 1 r27 res., chip, 105k, 1/16w, 1% , 0402 vishay, crcw0402105kfked 10 1 r28 res., chip, 0, 0402 vishay, crcw04020000z0ed 11 1 r29 res., chip, 0, 1/4w, 1% , 1206 vishay, crcw12060000z0ea 12 1 r30 res., chip, 0, 1/10w, 1%, 0603 vishay, crcw06030000z0ea 13 0 r31 to r34, r46 res., opt , 0402 opt 14 0 r35 to r45 res., opt , 0603 opt hardware 1 7 e2, e10, e11, e12, e16, e17, e18 testpoint, turret 0.094" millmax, 2501-2-00-80-00-00-07-0 2 20 e4 to e9, e13 to e15, e19 to e29 testpoint, turret 0.064" mill-max, 2308-2-00-80-00-00-07-0 3 2 j 1, j2 connector, banana jack keystone, 575-4 dc1784af demo manual dc1784a
7 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 en/uvlo led1+ led2+ led3+ ovlo ctrl1 ctrl2 ctrl3 intvcc flt1 flt2 flt3 sync out1 out2 out3 pwm1 pwm2 pwm3 gnd gnd gnd up to 50v led 1a gnd vin pvin gnd gnd gnd gnd 2.5v - 40v sd25-470-r 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 up to 50v led 1a up to 50v led 1a 310khz out1 led2+ out2 pvin out2 out3 out1 vin led3+ led1+ out3 pvin pvin pvin pvin pvin pvin intvcc pvin pvin pvin ref intvcc ref pvin pvin pvin m4 si7113dn m4 si7113dn 2 4 7 3 1 6 8 5 r36 opt 0603 r36 opt 0603 c12 6.8nf c12 6.8nf r38 opt r38 opt c31 c31 e8 e8 r37 opt 0603 r37 opt 0603 r9 23.2k r9 23.2k e26 e26 r29 0 1206 r29 0 1206 e20 e20 r2 0.25 2010 r2 0.25 2010 e2 e2 c29 c29 e17 e17 r43 opt 0603 r43 opt 0603 r20 140k r20 140k r3 0.25 2010 r3 0.25 2010 c6 4.7uf 100v 1210 c6 4.7uf 100v 1210 c34 opt 1210 c34 opt 1210 r8 23.2k r8 23.2k l1 10uh l1 10uh m6 si7113dn m6 si7113dn 2 4 7 3 1 6 8 5 d1 pds360 d1 pds360 1 2 3 m1 bsc039n06ns m1 bsc039n06ns 2 4 7 3 1 6 8 5 r26 100k r26 100k j2 j2 c14 0.1uf c14 0.1uf e19 e19 c27 c27 c35 opt 1210 c35 opt 1210 m2 si7113dn m2 si7113dn 2 4 7 3 1 6 8 5 r23 100k r23 100k r31 opt r31 opt e24 e24 r24 100k r24 100k r19 1m r19 1m r25 100k r25 100k + c37 33uf 50v + c37 33uf 50v e27 e27 r1 47.5k r1 47.5k r46 opt r46 opt c15 0.1uf c15 0.1uf r12 0.008 2010 r12 0.008 2010 c7 4.7uf 100v 1210 c7 4.7uf 100v 1210 r13 0.008 2010 r13 0.008 2010 j1 j1 e6 e6 r39 opt r39 opt c13 0.1uf c13 0.1uf c30 opt 1210 c30 opt 1210 e15 e15 d4 es1b d4 es1b 1 2 r45 opt 0603 r45 opt 0603 r30 0 r30 0 d3 pds360 d3 pds360 1 2 3 e16 e16 e9 e9 r4 0.25 2010 r4 0.25 2010 c28 1210 opt c28 1210 opt e10 e10 c19 c19 r5 3.9k r5 3.9k r21 140k r21 140k c32 c32 c25 c25 r44 opt 0603 r44 opt 0603 c3 4.7uf 50v 1210 c3 4.7uf 50v 1210 e14 e14 c26 opt 1210 c26 opt 1210 c11 6.8nf c11 6.8nf e28 e28 r7 3.9k r7 3.9k r42 opt 0603 r42 opt 0603 e21 e21 r10 23.2k r10 23.2k d2 pds360 d2 pds360 1 2 3 r15 1m r15 1m d5 es1b d5 es1b 1 2 c1 1uf 50v 0805 c1 1uf 50v 0805 c36 opt 1210 c36 opt 1210 r40 opt r40 opt c33 c33 c18 opt c18 opt c8 0.1uf c8 0.1uf r11 0.008 2010 r11 0.008 2010 r17 1m r17 1m c16 opt c16 opt c24 opt c24 opt r28 0 r28 0 e7 e7 d6 es1b d6 es1b 1 2 c4 4.7uf 50v 1210 c4 4.7uf 50v 1210 r22 140k r22 140k e4 e4 l2 10uh l2 10uh c9 10uf 10v c9 10uf 10v c2 4.7uf 50v 1210 c2 4.7uf 50v 1210 r41 opt 0603 r41 opt 0603 r27 105k r27 105k e29 e29 c22 opt c22 opt e11 e11 c20 c20 c5 4.7uf 100v 1210 c5 4.7uf 100v 1210 r34 opt r34 opt e12 e12 c17 opt c17 opt e22 e22 u1 LT3797EUKG u1 LT3797EUKG flt1 1 flt2 2 flt3 3 pwm1 4 pwm2 5 pwm3 6 ref 7 ctrl1 8 ctrl2 9 ctrl3 10 rt 11 sync 12 tg1 14 i sn1 15 i sp1 16 fbh1 17 vc1 19 ss1 20 sensen1 21 sensep1 22 gate1 23 gate2 24 sensep2 25 sensen2 26 ss2 27 vc2 28 fbh2 30 i sp2 31 i sn2 32 tg2 33 tg3 35 i sn3 36 i sp3 37 fbh3 38 vc3 40 ss3 41 sensen3 42 sensep3 43 gate3 44 int vcc 45 int vcc 46 sw2 47 boost 48 sw1 49 vin 50 en/uvlo 51 ovlo 52 gnd 53 r32 opt r32 opt c23 opt c23 opt e23 e23 l3 10uh l3 10uh e25 e25 e13 e13 e18 e18 r33 opt r33 opt m3 bsc039n06ns m3 bsc039n06ns 2 4 7 3 1 6 8 5 l4 47uh l4 47uh r6 3.9k r6 3.9k r35 opt 0603 r35 opt 0603 r14 1m r14 1m c10 6.8nf c10 6.8nf r18 1m r18 1m e5 e5 c21 c21 r16 1m r16 1m m5 bsc039n06ns m5 bsc039n06ns 2 4 7 3 1 6 8 5 dc1784af demo manual dc1784a
8 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com linear technology corporation 2014 lt 0114 ? 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 dc1784af demo manual dc1784a
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