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TPS25730: Help with VIN 3V3 pin

Brandon Kopinski
Prodigy 130 points
Part Number: TPS25730
Other Parts Discussed in Thread: TPS25751

In my application, I am using USB-C to power my entire product. There is no battery in the system, so I cannot provide external power to the VIN 3V3 pin when the USB-C isn't connected. I was planning on powering the TPS25730 with VBUS to initially turn on the device. Once the USB power is negotiated, I have an onboard 3.3V regulator (powered by the USB C negotiated power) that I want to feed into the VIN_3V3 pin of the TPS25730. If I clear the 'dead battery' condition, will the part seamlessly transition over from VBUS to the 3.3V rail that I'm feeding it? Or will that cause the part to glitch and restart?

Thanks,

Brandon

  • +1
    TI__Genius 13880 points

    Good Afternoon Brandon,

    If I clear the 'dead battery' condition, will the part seamlessly transition over from VBUS to the 3.3V rail that I'm feeding it? Or will that cause the part to glitch and restart?

    This part is designed to operate in dead battery mode. You can feed in VIN_3V3, however the part will continue to utilize the 3.3V from our internal LDO (that uses VBUS to drop to 3.3V).

    Our TPS25751 has the capability of clearing the dead battery flag to allow for powering the part from VIN_3V3 using the DBfg 4CC command. Using the TPS25751 and following your above protocol, there would be a seamless transition from VBUS to VIN_3V3 powering the part.

    Kind regards,

    Conner Gillette

  • 0 in reply to Conner Gillette
    Prodigy 130 points

    Hi Conner,

    Thanks for your reply! I'm a little confused. Below is an excerpt from the TPS25730 datasheet saying that the part will be powered by VBUS until the dead-battery flag is cleared. Then it will accept the voltage on the VIN_3V3 pin. Is the datasheet incorrect here?

    Also, if VIN_3V3 isn't used, do I still need to include the recommended 10uF capacitor on that pin? 

    Thanks for your help!

    Brandon

  • +1 in reply to Brandon Kopinski
    TI__Genius 13880 points

    The TPS25730 does not include the capability to clear the dead-battery flag, so the TPS25730 will always be powered from VBUS through its internal 3.3V LDO.

    Yes, it is still recommended to include the capacitor on the VIN_3V3 pin.

    Kind regards,

    Conner Gillette