DEMO MANUAL DC1706A LT3796 100V LED Controller with Current Monitor DESCRIPTION DC1706A is a 100V LED controller with an input current DC1706A PWM dimming is simple. The topside PWM + monitor. It is a single switch boost LED driver with LED dimming MOSFET (M2) turns the LED string on and off to GND short circuit protection. It accepts an input volt- with an input to the PWM dimming terminal. For the high- age from 8V to 100V (7.5V UVLO and 8.7V turn-on), and est PWM dimming ratio, it is recommended to use 100Hz drives up to 85V of LEDs at 400mA (when PVIN is less than as a PWM dimming frequency. Information regarding V ). DC1706A features both PWM and analog dimming PWM dimming ratios and performance can be found in LED of the LED string. It has a VMODE flag that indicates when the LT3796 data sheet in the applications section. Analog the LED string has been removed and it has a FAULT flag dimming is also simple to use with a single voltage source that indicates that the output has been shorted to GND. In on the CTRL terminal. both cases, the IC remains in control and well protected. Modifications can be made to DC1706A in order to convert DC1706A features high efficiency at 300kHz switching the board to higher or lower power or from an LED driver frequency. At high LED string voltages up to 85V and to a constant voltage regulator or battery charger. It can 400mA of LED current, the single switch controller has easily be changed from a boost topology to a SEPIC, buck 93% efficiency. There are input current (CSOUT) and out- mode, or buck-boost mode LED driver. Please consult the put current (ISMON) monitor pins that deliver a voltage factory or refer to the LT3796 data sheet for details. proportional to the current for quick diagnostics. The LT3796 data sheet gives a complete description of Small ceramic input and output capacitors are used to save the part, operation and applications information. The space and cost. The open LED overvoltage protection uses data sheet must be read in conjunction with this demo the ICs constant voltage regulation loop to regulate the manual for DC1706A. The LT3796 is assembled in a 28- output to approximately 92.5V if the LED string is opened lead plastic TSSOP FE package with a thermally enhanced although it may reach 96.5V peak during transient from ground pad. Proper board layout is essential for maximum running LEDs to open. thermal performance. See the data sheet section Layout Considerations. For low input voltage operation, the CTRL pin voltage is reduced as the input voltage drops below 9V, reducing Design files for this circuit board are available at LED brightness and restraining the peak switch currents DEMO MANUAL DC1706A PERFORMANCE SUMMARY (T = 25C) A PARAMETER CONDITIONS UNITS Input Voltage PVIN Range Operating 7.5V to V LED Switching Frequency R18 = 26.1k 300kHz I RS2 = 0.62, 9V < PVIN < V 400mA LED LED Low PVIN I (CTRL Foldback) RS2 = 0.62, PVIN = 8V 350mA LED V Range R5 = 1M, R9 = 13.7k PVIN < V < 85V LED LED Open LED Voltage R5 = 1M, R9 = 13.7k 92.5V Typical Efficiency PVIN = 14V, V = 85V, I = 400mA 93% LED LED Under Voltage Lockout (Falling Turn-Off) R1 = 499k and R8 = 100k 7.5V Under Voltage Lockout (Rising Turn-On) R1 = 499k and R8 = 100k 8.7V V Operating 7.7V INTVCC Peak Switch Current Limit RS3 = 0.015 6.6A Suggested Maximum PWM Dimming Ratio f = 100Hz, PVIN=12V, V = 85V, I = 400mA 100:1 PWM LED LED QUICK START PROCEDURE DC1706A is easy to set up to evaluate the performance of 5. Turn the input power supply on and make sure the the LT3796. Follow the procedure below: voltage is between 8V and V . LED NOTE: PWM must be pulled high to run. If PWM is not 6. Release the EN/UVLO-to-GND connection. used, connect PWM to a 3.3V or 5V source or to VREF on 7. Observe the LED string running at the programmed the PCB using 0 resistor R24. LED current. 1. Connect a string of LEDs that will run with forward volt- 8. Observe the CSOUT and ISMON input and output cur- + age less than 85V, but greater than PVIN, to the LED rent monitor voltages. and GND terminals on the PCB as shown in Figure 1. 9. For PWM dimming, connect a PWM (100Hz or higher is 2. Connect the EN/UVLO terminal to GND. recommended) signal to the PWM terminal. For analog 3. With power off, connect the input power supply to the dimming, connect a DC voltage between 0V and 2V to PVIN and GND terminals. Make sure that the PVIN DC the CTRL terminal. input voltage will not exceed 100V (or V ). LED 10. Observe the reduction of brightness in the LED string 4. Connect the PWM terminal. If PWM is not used, connect when PWM or analog dimming. PWM to a 3.3V or 5V source or to VREF on the PCB us- ing 0 resistor R24. PWM must be pulled high to run. dc1706af 2