DC1274A

DEMO MANUAL DC1274A LTM8040 36V, 1A Step-Down Module LED Driver DESCRIPTION Demo circuit DC1274A features the LTM 8040 36V, 1A frequency, lower the LED current, and implement PWM step-down constant current Module LED driver. The dimming. The shutdown feature can be examined by con- demonstration circuit is designed to drive a single LED necting the shutdown terminal to ground. The LTM8040 or string of LEDs at up to 1A from a wide input voltage data sheet must be read in conjunction with this demo range. The maximum LED string voltage is 13V and the manual prior to working on or modifying demo circuit minimum voltage varies depending upon the BIAS pin sup- DC1274A. ply arrangement. The demonstration circuit is assembled Design files for this circuit board are available at with the BIAS pin connected to the LEDA pin. DEMO MANUAL DC1274A QUICK START PROCEDURE DC1274A is an easy way to evaluate the LTM8040. Refer 4. Tie the shutdown terminal to ground in order to turn to the test procedures outlined below and Figure 1. the output off and examine the shutdown operation. Allow the IC to run by releasing the shutdown terminal 1. Make sure the power supply is less than 36V. With the connection to ground. The IC will run with the 100k supply OFF, connect it to the VIN and GND terminals. pull-up resistor from the shutdown terminal to VIN. 2. Connect an LED or string of LEDs between the LEDA For LEDs or LED strings with a low forward voltage such terminal and the GND terminal. For PWM dimming, the as a single red LED, the BIAS terminal can be disconnected PWM dimming MOSFET must be added to the PCB and from the output (LPWR) and tied to the input (VIN). There the string of LEDs must be attached between LEDA and is a small trace on the back of the PCB (layer 4) that can LED- terminals. However, for simplicity, the MOSFET is be cut in order to disconnect LPWR from BIAS. Please see not assembled on the board as shipped. the LTM8040 data sheet for details regarding the proper 3. Turn on the input power supply and set the voltage connection of the BIAS pin. between 4V and 36V based on the forward voltage of the LED(s) and desired output current. Please see the LTM8040 data sheet for details. dc1274af 2