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TPS7A30: soft start pin short

Aivaras Sakauskas
Intellectual 1600 points
Part Number: TPS7A30

Tool/software:

Hi,

If this pin is shorted to 0V in order to force and hold the output to 0V, would that work ok in this device (Vin will remain -30V all throughout).  For majority of the time, this soft-start pin will have a 1nF to 0V but, as a requirement, there is a need for 0V at the output instead of the normal LDO output voltage. Thinking of ways to achieve this with minimal circuitry. Are there other ideas?

Thanks

  • 0
    TI__Guru 50025 points

    Hi,

    Why can't you use the EN pin to turn off the device when you want the output to be 0V? The way I see it you will need some sort of logic signal to short the soft start to ground anyways so it seems like using EN would be simpler. 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    TI__Intellectual 1600 points

    Hi

    Thanks Nick for suggesting a possible resolution to this. If I am not mistaken, EN pin (when inactive) would normally put the output in high impedance state. Whereas shorting the Soft-Start to 0V would (possibly?) hold the output in 0V state (so it can sink/source current). Pulling down the output to 0V is not an option in this case I am afraid. Can you comment if this would be the case and do you have other suggestions for having the output at 0V?

  • 0 in reply to Aivaras Sakauskas
    TI__Guru 50025 points

    Hi,

    Aivaras Sakauskas said:
    If I am not mistaken, EN pin (when inactive) would normally put the output in high impedance state.

    You are correct.

    Aivaras Sakauskas said:
    Whereas shorting the Soft-Start to 0V would (possibly?) hold the output in 0V state (so it can sink/source current). Pulling down the output to 0V is not an option in this case I am afraid. Can you comment if this would be the case and do you have other suggestions for having the output at 0V?

    If the NR/SS pin is pulled to ground, the output becomes high impedance just as if the EN pin was pulled low, so it wouldn't help to do this. Only devices that have an active pull down circuit on the output can sink current in any case, but we don't have any negative LDOs with an active pull down. 

    Another idea could be to use a couple transistors to use the EN signal to pull the output to 0V with a series resistor so that the output is discharged when the device should be off. 

    Regards,

    Nick