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.