DC1436A Analog Devices

DEMO CIRCUIT 1436A 16-CHANNEL High VOLTAGE LED DRIVER LT3754 DESCRIPTION DC1436A is a 16-Channel High Voltage LED tied in parallel by tying their LED1-16 pins to- Driver featuring the LT3754. The LT3754 drives gether. up to 50mA per string and has a maximum LED The LT3754 datasheet gives a complete de- string voltage of 45V. DC1436A is set at 1MHz scription of the part, operation and applications switching frequency for smallest inductor and information. The datasheet must be read in capacitor size as well as maximum PWM dim- conjunction with this Quick Start Guide for ming performance. Overvoltage protection is demonstration circuit 1436A. The LT3754 is as- set at 55V in case the LEDs are removed from sembled in a small 32-lead (5mm x 5mm) QFN the circuit. If the LEDs are opened, the FAULT package with a thermally enhanced ground terminal output flag goes low and reports the pad. Proper board layout is essential for maxi- fault condition. The VIN terminal is powered mum thermal performance. See the datasheet from 10-14V input separated from the 24V section Layout Considerations. PVIN supply for best thermal performance. If Design files for this circuit board are avail- one or more of the 16 LED channels is not able. Call the LTC factory. used, its LED pin or terminal should be tied to LED+ to disable it. Multiple channels can be LT is a trademark of Linear Technology Corporation Table 1. Typical Performance Summary for DC1436A PARAMETER CONDITION VALUE (TYPICAL) PVIN Power Input Voltage Range Operating 20V - 28V VIN Pin Input Voltage Range Operating 8V - 14V Switching Frequency RT=39.2k 1MHz LED String Current I R14=5.76k 50mA LED(1-16) OVP Open LED Voltage R8=11k R7=20k 55V Efficiency PVIN=24V VIN=10V V =45V 92% LED I =50mA LED1-16 Under Voltage Lockout 20.1V R1=499k R4=40.2k Low Voltage Turn-On (UVLO + V ) 21.4V HYST Peak Switch Current Limit RS1 = 0.015 3.3A 1 DEMO CIRCUIT 1436A 16-CHANNEL High VOLTAGE LED DRIVER does not exceed the forward voltage of the LED string. QUICK START PROCEDURE 4. With power off, connect the VIN power sup- ply to the VIN and GND terminals within the Demonstration circuit 1436A is easy to set up range specified on the PCB. to evaluate the performance of the LT3754. Follow the procedure below: 5. Connect the PWM terminal. If PWM is not used, tie PWM high or connect to REF on NOTE: PWM must be pulled high to work. If the PCB using resistor R9. PWM must be PWM is not used, tie PWM high or connect to pulled high to work. REF on the PCB using resistor R9. 6. Turn the PVIN power supply on. 1. Connect strings of LEDs with forward volt- age less than 45V, but greater than the 7. Turn the VIN power supply on after PVIN. PVIN voltage, to the LED+ and LED1-16 8. Release the shutdown-to-GND connection. terminals on the PCB as shown in Figure 1. Tie any unused LED1-16 pins directly to 9. Observe the LED strings running at the pro- VOUT (LED+) to disable that channel. grammed LED current. 2. Connect the shutdown terminal to GND. NOTE: For PWM dimming, connect a PWM (100Hz or higher) signal to the PWM terminal 3. With power off, connect the PVIN power and observe the reduction of brightness in the supply to the PVIN and GND terminals LED string when PWM dimming. within the range specified on the PCB. Make sure that the PVIN DC input voltage 2