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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT

1268A-A, 1268A-B

HIGH VOLTAGE LED CONTROLLER

R18

OPT

R17

22k

22.1k

Si7850DP

LED+

4.7uF

LED-
BOOST

LED-
BUCK / BUCK-BOOST M ODES

RS2

0.10

140k

PVIN BUCK M ODE

INTVCC

Si2308DS

1uF

50V

OPENLED

R14

OPT

22uH

PWMD

PDS560

R13

OPT

R10

100k

OPT

RS1

0.015

90.9k

0.1uF

CTRL

0 ohm

28.7k

R15

LT3755EUD

SD/UV

PWM

INTVCC

VREF

CTRL

OPENLED

VIN

ISP

ISN

PWMOUT

GATE

SENSE

GND

499k

0 Ohm

Cout

3x 2.2uF

100V

400kHz

2200pF

C1, C10

2x 4.7uF

50V

OPT

10V

PVIN 8V to 40V

PWMD

HC9-220-R

PWM

Figure 2. DC1268A-A featuring LT3755 and Open LED flag.

Summary of Contents for LT3755

Page 1: ...268A PWM dimming is simple The boost topol ogy LED string returns to the LED terminal and the PWM dimming MOSFET turns the LED string on and off given 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 LT3755 1 datasheet in the applica tions sec...

Page 2: ...nput voltage does not exceed 40V 1 Connect a string of LEDs with forward voltage less than 55V but greater than the PVIN voltage to the LED and LED Boost terminals on the PCB as shown in Figure 1 2 Connect the shutdown terminal to GND 3 With power off connect the PVIN power supply to the PVIN and GND terminals within the ranges specified on the PCB 4 Connect the PWM terminal If PWM is not used con...

Page 3: ...attached to this docu ment The open LED indicator terminal has a pull up resistor to the internal 7V regulator IntVcc The B version with the sync terminal has an RC filter between the PWM input pin and the SYNC input pin This filter provides a small delay between the PWM signal and the SYNC input when PWM is used in order to optimize high PWM dimming ratio waveforms If high ratios are not needed t...

Page 4: ...tor R2 can be re moved and the VIN terminal can be connected to a separate supply from the PVIN terminal The VIN ter minal is tied directly to the VIN pin The VOUT terminal is available for the customer to monitor the state of the output capacitor directly The VOUT terminal can also be used as an input for buck mode topology The PWM terminal must be pulled high in order for the board to operate It...

Page 5: ...LED R14 OPT L1 22uH PWMD D1 PDS560 R13 OPT R10 100k R5 OPT R6 1M RS1 0 015 R4 90 9k C7 0 1uF CTRL R2 0 ohm R8 28 7k R15 1M U1 LT3755EUD 6 2 7 15 4 1 16 5 3 8 14 13 11 10 12 9 17 SD UV PWM INTVCC VC SS VREF CTRL RT OPENLED VIN ISP ISN PWMOUT GATE FB SENSE GND R1 499k SD R3 0 Ohm Cout 3x 2 2uF 100V 400kHz C6 2200pF C1 C10 2x 4 7uF 50V C9 OPT Q3 OPT C8 OPT 10V PVIN 8V to 40V PWMD HC9 220 R PWM Figure...

Page 6: ... 84 86 88 90 92 94 96 98 100 5 10 15 20 25 30 35 40 INPUT VOLTAGE V EFFICIENCY Figure3 DC1268A A B Efficiency with 50V LEDs at 1A 0 0 0 2 0 4 0 6 0 8 1 0 1 2 5 10 15 20 25 30 35 40 INPUT VOLTAGE V LED CURRENT A Figure4 DC1268A A B LED Current Drops at Low VIN CTRL and Turns Off at Lower VIN UVLO ...

Page 7: ...INTVCC VC SS VREF CTRL RT SYNC VIN ISP ISN PWMOUT GATE FB SENSE GND LED BOOST LED BUCK BUCK BOOST MODES C4 1uF 50V HC9 220 R R13 OPT D1 PDS560 SD C7 0 1uF RS1 0 015 R2 0 ohm PWMD Q1 Si2308DS C6 2200pF LED CTRL Cout 3x 2 2uF 100V PWMD R10 OPT R17 22k R1 499k R3 0 Ohm INTVCC RS2 0 10 SYNC 400kHz R8 28 7k C9 OPT R4 90 9k PVIN BUCK MODE PVIN 8V to 40V R15 1M C8 100pF R14 OPT R5 OPT R7 140k 10V Figure5...

Page 8: ...4 510 R10 100k Cfilt1 22uF PWM 10V C6 4700pF L1 22uH 14V U1 LT3755EUD 6 2 7 15 4 1 16 5 3 8 14 13 11 10 12 9 17 SD UV PWM INTVCC VC SS VREF CTRL RT OPENLED VIN ISP ISN PWMOUT GATE FB SENSE GND RS1 0 025 Q3 Si2319DS SD R15 549k C7 0 01uF R17 4 7k D1 PDS560 800mA R3 0 Ohm C1 C10 2x 2 2uF 50V PVIN 8V to 36V C5 4 7uF Q2 Si7850DP 400kHz R7 75 0k LED LED BUCK BOOST MODE Figure6 DC1268A A Customized Buck...

Page 9: ... Rx1 1M Rx4 365 R17 15k U1 LT3755EUD 6 2 7 15 4 1 16 5 3 8 14 13 11 10 12 9 17 SD UV PWM INTVCC VC SS VREF CTRL RT OPENLED VIN ISP ISN PWMOUT GATE FB SENSE GND C7 0 01uF R9 22 1k LED C6 2200pF R8 28 7k R10 100k 400kHz R4 267k C9 22uF 16V C2 C3 2x 2 2uF 50V Rx2 100k C4 1uF 50V RS2 0 068 R5 0 Rx3 249k 10V L1 10uH PWM Q3 Si1471DH Qx1 2222 R3 0 CDRH8D43 Figure7 DC1268A A Customized Buck Mode LED Drive...

Page 10: ...3 C7 0 01uF RS2 0 10 50V 35V LED L1 22uH CTRL U1 LT3755EUD 1 6 2 7 15 4 1 16 5 3 8 14 13 11 10 12 9 17 SD UV PWM INTVCC VC SS VREF CTRL RT SYNC VIN ISP ISN PWMOUT GATE FB SENSE GND BOOST R18 10k SD 1A D1 PDS3100 C6 22nF R1 499k R6 732k 350kHz Q1 Si2318DS 10V R2 0 ohm R3 0 Ohm R9 24 9k PWM C8 100pF L2 33uH R17 51k R4 84 5k LED Figure8 DC1268A B Customized SEPIC Schematic with PWM Dimming and Alumin...

Page 11: ...QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1268A A 1268A B HIGH VOLTAGE LED CONTROLLER 11 ...

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