TPS65994AD: Source-role-only DFP design in dead-battery startup condition

Hi,

We are debugging our source-role-only, no battery, DFP design on the EVM board in dead-battery startup condition and encountering the following issues:

• When EVM is in dead-battery startup condition, the voltage on VBUS is oscillating. From PD analyzer logs it is observed the port is repeating VBUS down/up/negotiation periodically.
• Applying external power to EVM would intermittently result in the port to indicate: 
  
  • Reg. 0x1A
    • PlugPresent = No plug is connected
    • ConnState = No connection
    • Port Role = Sink
    • Data Role = UFP
    • VbusStatus = less than 0.8V
  • Reg. 0x28
    • Type-C state machine = disabled (CC pins are hi-z)
  • Reg. 0x2D
    • Dead Battery Flag = True
  • No way to recover by any port un-plug/re-plug

(Sending 'Clear Dead Battery Flag' command could bring the port back to expected source-role-only, DFP state)

Question:

1. We tried to change PD settings from 'source state machine only' to 'DRP state machine' which would prevent VBUS from oscillating and when external power applied to EVM the port connection is recognized. However, every time recovering from dead battery startup condition the port is always in sink role and UFP. How to configure the PD to always act as source only role and DFP when recovering from dead-battery startup condition?
2. Does PD always rely on its host communication to send 'Clear Dead Battery Flag' command when recovering from dead-battery startup condition? In TPS65994AD design resource package, an UCMCx Win10 driver is included. Is this UCMCx driver implemented with the policy to send 'Clear Dead Battery Flag' command to PD once dead-battery flag is set?

The PD configuration under debugging is attached for reference.

Thanks,

Jonathan Liang

3581.tps65994ad_evm_dbsc_20220316.pjt