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LMZ31707: Status LED Circuit on PWRGD Pin

Brian Clark
Prodigy 30 points
Part Number: LMZ31707

Hi,

I'm looking to implement a status LED on the PWRGD pin of a LMZ31707RVQ.  Are there any default configurations from TI for this? If not, can you provide some recommendations? The datasheet notes a pullup resistor (10k-100k) to a 5V supply is necessary, but nothing beyond that.

Thanks.

  • 0
    TI__Mastermind 18370 points

    Hi,

    I am guessing that you want the LED to turn-on when a problem is detected (Red LED).

    In this case, you will need a high efficiency/ low current LED (< 2mA) and a 1.25 KOhms resistor in series that connect between the PWRGND and 5V supply voltage.

    The current will be set by ( 5V - LED_forward_voltage)/1.25 KOhms , since the LED_forward_voltage is usually around 2.5V, this will lead to (5V-2.5V)/1.25KOhms = 2 mA. 

    The LMZ31707 electrical table says that PWRGND pin can sink 0.5 mA, but I believe it should be able to deal with 2 mA,.

    Regards,

    Yitzhak Bolurian

  • 0 in reply to Yitzhak Bolurian
    Prodigy 30 points

    Hi Yitzhak,

    Thank you for the quick reply!  This should be easy to implement, but I have one final question.  Do I still need the 10k-100kOhm pull up resistor in series with the 5V supply in addition to the 1.25kOhm resistor and LED?

    Thanks,

    Brian

  • +1 in reply to Brian Clark
    TI__Mastermind 18370 points

    Hi Brian,

    No extra pull up. The 1.25KOhms resistor and the LED is all you need.

    Regards,

    Yitzhak