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TPS22991: Quick output discharge when power is disconnected

John Griffith
Mastermind 21636 points
Part Number: TPS22991
Other Parts Discussed in Thread: TPS22995

Tool/software:

Hello,

I want to confirm if the quick output discharge circuit ever gets activated when the input power drops out. My customer has a buck boost circuit that takes too long to discharge when input power is removed and I was hoping a power switch with QOD could help solve the problem. Open to other ideas as well! 

Could a voltage divider on the ON pin help enable the QOD for a short period? Looks like rising edge is 0.8V and falling edge is 0.35V. 

John

  • 0
    TI__Mastermind 27520 points

    Hi John,

    QOD won't trigger when the device is on. Solution of using voltage divider from Vin to control ON pin should work. 

    Best Regards,
    Arush

  • 0 in reply to Arush Gupta
    TI__Mastermind 21636 points

    Thanks Arush, I am not sure this will work well after doing some math on this idea. 

    Since the QOD will not trigger when the device is off, the voltage divider will set both rising and falling thresholds. The ON pin has a rising threshold of 0.8V and a falling threshold of 0.35V. So  with a 3.3V output, we could make the rising threshold trip and turn on at 3.2V for example, resulting in a 1:4 resistor divider ratio on the ON pin between VIN and GND. This means that when the supply starts to fall, the device will shut off as low as 1.4V (0.35 * 4 for the 4:1 ratio) and drive the output low until the supply dropped below 1.0V on VIN and the device shuts off. So essentially the QOD would drive the output low for only 400mV of the dropping voltage on VIN. Feels like this might not be enough.

    Any switched that you think that might work better?

    John

  • 0 in reply to John Griffith
    TI__Mastermind 27520 points

    Hi John,

    Will load switch with separate Vbias an option in the end application. Device like TPS22995 have QOD and separate Vbias. 

    Best Regards,
    Arush

  • 0 in reply to Arush Gupta
    TI__Mastermind 21636 points

    Hi Arush,

    That is a good idea. Just to double check, we could diode block VBIAS (resulting in a Schottky diode lower voltage on bias) and then tie VIN and ON (with a resistor divider) to the supply that we are passing on. Then when the input voltage drops the output will be disabled while the VBIAS still being available thus enabling the QOD.

    Make sense?

    John

  • 0 in reply to John Griffith
    TI__Mastermind 27520 points

    Hi John,

    I missed your reply. I apologies for that.

    Yes, what you mentioned makes sense. We will have to check the exact details on how much drop and resistor ratio to use but this should work.

    Best Regards,
    Arush