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LMR33630: How to connect an LED to indicate Power is Good from an Open Drain

Gee Won Han
Prodigy 10 points
Part Number: LMR33630

Tool/software:

Connecting a series of resistor and LED to the PG pin (open drain) would not work where I would like the LED to indicate Power is good. Since PG pin goes low if the power is bad and have high impedance  if the power is good. Is there a way to have the LED turn ON when power is good? 

I have seen other forums using a MOSFET using the PG signal on the Gate to turn ON/OFF the LED

I don't understand how an high impendence would do that

  • 0
    TI__Genius 9460 points

    You would need a pull up resistor from PG to Vcc and make a connection to the gate of a FET before the resistor. 

    For example if you are using a NMOS, source is Gnd, drain is cathode of LED and anode of LED is connected to Vcc through resistor. 

    When PG is low: NMOS gate -> 0V, LED is off

    When PG is high: NMOS gate -> Vcc, NMOS turns on and current flows through LED

    I would recommend testing LEDs and NMOS using a power supply to mimic PG before you design a board

    Regards,

    Rahil