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Original question:

TPS25750: Force using VBUS as power supply

TPS25750: Sink path not enabled

Jan Van Bogaert
Prodigy 80 points
Part Number: TPS25750
Other Parts Discussed in Thread: BQ25792

Tool/software:

Hi, 

I use the TPS25750 with the BQ25792 in a battery operated device.

The device is strapped for "always enable sink"    in dead battery mode.

When the battery is discharging, at a certain moment the main processor stops operating and for some reason the TPS25750 enters BATCH mode ( perhaps by spike on VIN ? ).

Because there is still about 3V on the VIN_3V3 pin, the TPS25750 does not enter dead battery mode.

When I connect a USB power supply, the TPS25750 does not switch the USB power towards the BQ25792, so the battery cannot recharge and the system is therefor in a deadlock.

Is there a way I can resolve that?  One nice solution would be to instruct the main processor to put the TPS25750 in dead battery mode when battery becomes dangerously low, but there is no system task for this.

Is there another solution for this problem?   Could it be solved by configuring the TPS25750 in "sink only"   mode for instance? Now iyt is configured for sink and source.

  • 0
    TI__Mastermind 37855 points

    Hi Jan,

    Jan Van Bogaert said:
    When the battery is discharging, at a certain moment the main processor stops operating and for some reason the TPS25750 enters BATCH mode ( perhaps by spike on VIN ? ).

    Batch mode or PTCH mode? If the PD controller is not in APP mode, you will not be able to configure the part as some of the registers are not available in PTCH mode.

    If it is going into PTCH mode, it sounds like the PD controller may be losing power and re-booting. Does your system load the patch bundle from the processor or from an EEPROM?

    Jan Van Bogaert said:
    Is there a way I can resolve that?  One nice solution would be to instruct the main processor to put the TPS25750 in dead battery mode when battery becomes dangerously low, but there is no system task for this.

    Unfortunately there is no "dead battery" enable functionality.

    Jan Van Bogaert said:
    Is there another solution for this problem?   Could it be solved by configuring the TPS25750 in "sink only"   mode for instance? Now iyt is configured for sink and source.

    As you noticed, dead battery effectively puts the device into a sink preferred state. Yes, it may be resolved by configuring the port as sink only when you know the battery is under a certain threshold. If the device is in PTCH mode, this likely will not work.

    The main processor could instruct the TPS25750 to be sink only when the battery becomes dangerously low.

    Another potential solution is to adjust the UVLO of your 3.3-V rail to completely shut off when a certain threshold is hit to remove power from the TPS25750. This might not work with other ICs on the rail though, so may not be an option.

    Thanks and Regards,

    Chris