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TPS22943: Will it be it okay if "ON" pin enabled prior to “VIN” power on？

Jiayu Ye
Intellectual 1790 points
Part Number: TPS22943

Dear TI,

Here we have a special application occasion that TPS22943 will be enabled prior to "VIN" power on, will it be okay? Any risk? Thanks.

  • 0
    TI__Mastermind 32650 points

    Hi Jiayu,

    It is possible to have ON high before VIN goes high. This operating method will cause the device to start turning on as soon as VIN rises above the minimum recommended voltage.

    While this is not incorrect operation, the timing of the switch will be affected as VIN continues to rise as the switch turns on. 

  • 0 in reply to Shreyas Dmello
    TI__Intellectual 1790 points

    Hi  Shreyas Dmello

    Thank you very much for your reply.

    (1) So it's okay if have ON high before VIN goes high, right? Although I know it's an uncommon application.

    (2) Actually, I am not clear about "While this is not incorrect operation, the timing of the switch will be affected as VIN continues to rise as the switch turns on. "

    (3) One additional question about the spec. I think we should use the ILM(min) and tBLANK(min) to calculate the Coutmax.

  • 0 in reply to Jiayu Ye
    TI__Mastermind 32650 points

    Hi Jiayu,

    1. Yes it is okay to run the device like this.

    2. The on time and rise time specifications on the datasheet assume that the input voltage rail is already high and stable. So in this situation where the ON is held high and VIN rises up, the switch will start to turn on as soon as the voltage rises above 1.62V. If the VIN ramp is slow, then the device could technically finish its "delay + turn on time" before the voltage rail stabilizes resulting in the rise time being limited by the ramp of the VIN supply. If this is acceptable, then there is no issue.

    3. Do note that this formula is talking about the maximum possible capacitance that can be filled. For a conservative estimate to make sure that all devices used can fill, I would suggest you use ILM(MIN). We will look into making this clearer.

  • 0 in reply to Shreyas Dmello
    TI__Intellectual 1790 points

    Hi Shreyas Dmello,

    Thank you very much for your patient explanation. I got it.