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BQ24195 Boost Mode question

Wu JW
Intellectual 2935 points
Other Parts Discussed in Thread: BQ24195

Hi,

During the boost mode for the BQ24195, how about the VBUS voltage? BQ24195 has the reverse protection MOSFET Q1 as in the IC internal, how can it work? Is it OFF during the BOOST Mode?

  • 0
    TI__Expert 8230 points

    Hello Wu,

    During OTG operation, the PMID pin provides the output. The internal Q1 is enabled so the VBUS voltage would also be ~5V.

    To prevent any issues if the VBUS is connected, there is a circuit in the datasheet that provides redundancy to disable/enable OTG based on VBUS connection.

    If Vbus is connected, Q1/Q2 will provide power to the device while Q3 pulls low the OTG pin, disabling OTG functionality.

    Hope this helps.

  • 0 in reply to Fernando Lopez
    TI__Intellectual 2935 points

    Hi, Fernando,

    Thanks for your feedback!

    Still have one confusion. If the VBUS has the 5V output, it looks the REGN can't work with the Boost mode as said in the datasheet. One of the condition for the Boost mode, is the VBUS< Battery +Vsleepz.

    If the REGN doesn't work, the boost mode shouldn't work in same time.

    So could you give me some suggestion for this?

    Another question: If the VBUS can support the 5V output, can we draw the 2A output for the load at this pin?

  • 0 in reply to Wu JW
    TI__Expert 8230 points
    Hello Wu,

    If using a device meant for powerbank applications, such as the bq24195, the RBFET will be turned off during boost operation, so the output of the boost will be on PMID.

    If VBUS=5V , that means the boost mode will be disabled, and the REGN will be powered by the VBUS for buck mode operation.
  • 0 in reply to Fernando Lopez
    TI__Intellectual 2935 points

    Hi, Fernando,

    More confusion. My early question: How about the VBUS during the boost mode. You said the VBUS should be 5V and the internal MOSFET should be on.

    Now, you said the RBFET should be Off. Which one is right? Thanks!

    If the VBUS no output during the BOOST mode. and VBUS should be < UVLOZ, and the REGN LDO should be OFF as said in the datasheet. If there is no REGN, it looks the BOOST mode can't work, there is no driver for the MOSFET.

  • 0 in reply to Wu JW
    TI__Expert 8230 points

    Hello Wu,

    Sorry for the confusion, I was referring to the non-powerbank devices. On the bq24195, the Q1 FET should be off when boost mode is enabled. Just verified this on the EVM as well.

    The REGN is also powered by the battery during boost mode while the battery voltage is above the BATLOWV threshold.

  • 0 in reply to Fernando Lopez
    TI__Intellectual 2935 points

    Hi, Fernando,

    Thanks a lot for your clarify!

    Is there some mistake in the datasheet? As in boost mode the VBUS should be low, the Q1 Off, and Vbus should be < UVLOZ. As in the datasheet said, the REGN should be off. Could you help check it?

  • 0 in reply to Wu JW
    TI__Expert 8230 points

    Hello Wu,

    The conditions you are referring to on the datasheet for REGN enable are correct, as well as the HIZ mode with REGN LDO off. Perhaps the item that can be added for further clarification is that during boost mode, without VBUS connected or VBUS below battery+Vsleepz, REGN is powered from the battery. while battery is above BATLOWV.