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LM2936: add a delay using the SD pin

domenyko
Genius 9655 points
Part Number: LM2936

Dear all,

can you suggest a circuit to generate a delayed power on using the SD pin ? The LM2936 has a SD which works in the opposite way respect with most of similar devices.

regards,

Domenico 

  • 0
    TI__Guru 55940 points

    Hi Domenico,

    Often people will use a GPIO of another device in their application to programmatically sequence their different voltage rails; however, there are other options if this is not available in your system.  Another method is to use a SVS such as TPS3896P or TPS3898P.  The other common method is to use a RC delay.  You would still place the resistor between the source of Ven and the capacitor like you would for a delay on a EN pin; however, in this case you will be discharging the capacitor instead of charging the capacitor for the delay time.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    TI__Genius 9655 points

    Hi Ryan,

    thanks, I was thinking to the RC approach. usually you connect the source of the EN pin (in this case SD) to the VIN with RC circuit. But in this case what do you suggest  to discharge the capacitance ?

    regards,

    Domenico

  • 0 in reply to domenyko
    TI__Guru 55940 points
    Hi Domenico,

    You will still need to drive the SD pin with a signal just like you would with an EN pin on another LDO. When you drive the SD pin to logic low (GND), the discharge path for your capacitor will be through the resistor into the source you are using to drive the SD pin.

    Very Respectfully,
    Ryan