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BQ24295: Power management forum

Amit Pandey
Prodigy 20 points
Part Number: BQ24295
Other Parts Discussed in Thread: BQ24296

Tool/software:

I have a concern regarding the use of the BQ24295 charging IC in our custom circuit.

In our design, we are using both the SYS and PMID pins. The logic is set such that:

  • When the battery voltage is above 3.5V, the system runs from SYS.

  • When the battery voltage is below 3.5V, it switches to PMID.

This logic works well. However, when the system is running from PMID, we still observe a continuous input voltage (e.g., 4.3V or 3.6V) appearing at the SYS pin.

Since SYS is an output pin, I am concerned that this could negatively affect the IC—possibly by back-powering the output or causing internal conflict.

Can you please confirm if this behavior is safe, or if it could damage or interfere with the IC’s normal operation?

  • 0
    TI__Guru 57651 points

    Hi,

    You mentioned "When the battery voltage is below 3.5V, it switches to PMID." Are you referring to OTG mode supports PMID output?

    Thanks,

    Ning

  • 0 in reply to Ning T
    Prodigy 20 points

    Hello Ning,

    I’m working on a design using the BQ24296 where I’ve implemented a logic circuit that enables or disables OTG mode based on the battery voltage.

    Specifically, I’ve created a system where:

    • If VBAT > 3.5V, SYS is enabled and PMID is disabled.

    • If VBAT < 3.5V, then the system switches to PMID and SYS is disabled.

    My intention is to utilize both SYS and PMID as power sources (through MOSFETs), and the load shares a common power rail. For example:

    • One MOSFET connects SYS to the load when the battery voltage is sufficient.

    • Another MOSFET connects PMID to the same load when the battery voltage is low.

    Since SYS follows the battery voltage, during SYS operation, the load rail reflects battery voltage. But because both SYS and PMID are connected to the same load (just switched via MOSFETs), there are conditions where one pin (like SYS) could see voltage while the IC is operating from the other source (like PMID).

    My concern is:
    Could this back-voltage condition on SYS or PMID (due to shared load rail) potentially harm the BQ24296 or cause abnormal behavior?
    I’d appreciate your guidance on whether this approach is safe, or if additional protection (like diodes or isolation) is required.

    Looking forward to your advice.

  • 0 in reply to Amit Pandey
    TI__Guru 57651 points

    Hi,

    There's Q2 between PMID and SW. The device should be ok under normal operations.

    Thanks,

    Ning

  • 0 in reply to Ning T
    Prodigy 20 points

    Hi Ning,

    I understand that both SYS and PMID are output pins, but in my application, due to shared load through external MOSFET switching, there might be cases where voltage in the range of 3.5V to 3.8V is present at the SYS pin, even when SYS is not actively supplying the load.

    My concern is:
     Will applying 3.5V to 3.8V externally at the SYS pin cause any damage to the BQ24296, or is it safe under such conditions?

    This voltage could appear due to the shared load rail, depending on the active power path (SYS or PMID). I want to ensure that this won’t create a back-power issue or affect the IC’s behavior.

    Looking forward to your confirmation.

  • 0 in reply to Amit Pandey
    TI__Guru 57651 points

    Hi,

    If there's no overvoltage or overcurrent condition at the SYS pin or on the device, it should be ok.

    Thanks,

    Ning