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TPS62480: About 'power good' signal behavior before VIN supplied.

Tomo
Prodigy 210 points
Part Number: TPS62480

Hi, all

Could you tell me about 'power good signal' before VIN supplied.
Will device keep pulling to low this signal?
Or, will it floating until VIN level goes to minimum input voltage(=2.6V) ?

Best regards,

tomo

  • +1
    TI__Mastermind 20900 points

    Hi Tomo,

    The PG pin goes High, when the output voltage has reached its nominal value. Otherwise, including when disabled, in UVLO or thermal shutdown, PG is Low. 

    Typically, before providing VIN, there is nothing powering the comparators and logic “defining” the power-good state. At this time (before applying power), the open-drain FET’s gate voltage is determined by leakages and is more likely to turn off than to turn on. If the PG pin is pulled-up with a resistor to the output voltage; but device disabled; therefore no output voltage, the PG pin will have a low state.

    But in this case, is the device externally enabled? 

    Is the PG pin externally biased?

    Regards,

    Febin

  • 0 in reply to Febin
    Prodigy 210 points

    In my circuit I am using this IC to generate for 1.2V from 3.3V, and I am considering which of VIN and VOUT is better for pull-up.
    If I select VOUT for pull-up voltage, receiver IC may not receive PG signal because voltage is too low.
    But if select VIN for pull-up voltage, I thought PG pin will pulling-up by VIN only for a short time when VIN ramp-up. It is not good for my circuit.
    I consider another way to avoid undefined state of VIN ramp-up.
    Thank you very much!

    Regards,
    tomo

  • 0 in reply to Tomo
    TI__Mastermind 20900 points

    Hi Tomo,

    I am not sure if I understood you correctly. I do not see a problem if you connect PG to Vout (1.2V). When the rising edge reaches 96% of Vout, PG will have a logic HIGH. 

    Is there something I misinterpreted?

    Regards,

    Febin

  • 0 in reply to Febin
    Prodigy 210 points

    Thank you for your reply.
    Also, I think this IC will working normally even if the PG pin is pulled up by VOUT.
    But I wanted to connect PG signal to 'ON' pin of the TPS22965DSG.
    TPS22965DSG's 'ON' pin voltage is 1.1V minimum.
    Since these voltages are about the same, I was worried that the TPS22965DSG might not work properly in all environments.
    It is reason why I could not decide to pull-up by VOUT.
    Regards,
    tomo

  • 0 in reply to Tomo
    TI__Mastermind 20900 points

    Hi Tomo,

    I got your point. In that case, you can also connect PG to Vin or use an external bias.

    Regards,

    Febin