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TUSB321: Dead battery support when configured as a Dual Role Port (DRP)

Martin Clemons
Prodigy 80 points
Part Number: TUSB321
Other Parts Discussed in Thread: BQ24773

The USB-C port on our device will be configured as a Dual Role Port (DRP), and configuring the TUSB321 for this role is simple enough. What seems to be missing from the datasheet however is any discussion of “dead battery mode” where the device is no longer able to supply VDD to the TUSB321, but power delivery must still take place when connected to a charger/DFP.

The TUSB321 parametric description page states that the IC supports dead battery mode (www.ti.com/.../description), but I’m not able to find how exactly things need to be connected to support this.

Basically, I need to:
1. power up the the TUSB321 and our µC,
2. sense that the DRP is connected as a UFP and determine the allowed charging current based on the TUSB321 outputs,
3. switch the power path from VBUS to the bq24773 on

I need to be able to do this both when the TUSB321 is powered internally from our device as well as when it is powered externally from VBUS.
Based on some reading I’ve done, it may be as simple as adding a schottky diode from VBUS to VDD on the TUSB321 and the µC power regulator, but I wasn’t able to find any documentation addressing this specific scenario.

  • 0
    TI__Mastermind 36085 points
    Hello Martin,

    In order to set the TUSB321 in dead battery mode you only need to remove VDD. When VDD is off, The TUSB321 presents the Rd terminations on the CC pins (5.1KOhm Pull-down), so the attached device on the otherside of the type-C cable can detect the TUSB321 as UFP device and will provide VBUS to charge & power-up the TUSB321.

    So the dead battery case when the TUSB321 is powered internally makes no sense at all (because dead battery requires VDD=0V).

    Regards,
    Diego.