LT3474 SHDN pin control

Hi, I want to use MCU pin to control SHDN pin of LT3474.

As in the datasheet, I see the LT3474 doesn't have the internal pull down resistor so I must to use external resistor to pull down on the SHDN line, right?

This is a discussion with my colleague and he doesn't want to use external resistor. Please let me know what is correct.

  • Hello,

    If your MCU can drive its digital outputs high/low you shouldn't need any external resistors on the SHDN pin. Assuming the digital outputs can properly drive the SHDN pin, you should just be able to connect the MCU output directly to SHDN with common grounding between the two devices. The SHDN pin needs greater than 2.65V to enable the part, and less than 0.3V to disable the part. You will need to ensure that your MCU can pull the pin all the way below 0.3V to guarantee shutdown, as well as drive the pin higher than 2.65V to ensure it is turned on. 

  • I forgot to say that the pull-down resistor on SHDN is used to prevent floating state on GPIO control pin of MCU when it has been reset. It maybe high when reset and then active the LT3474. In this case the LED can be flashed?