TPS65987D: Inconsistent PD Negotiation

Prodigy 10 points

Replies: 1

Views: 41

Part Number: TPS65987D

My application is setup as follows:

  1. BP_NoWait
  2. Configuration 3
  3. Dead Battery Mode and using a TPD6S300
  4. VBUS1 connects to USBC
  5. VBUS2 is grounded
  6. PP_HV1 is output
  7. PP_HV2 is grounded
  8. GPIO0 connected to GPIO1 then connected to ground via 1M Ohm
  9. PP_CABLE connected to VIN_3V3
  10. No external mux
  11. No external firmware
  12. CY4500 EZ-PD is connected to spy on negotiation
  13. USBC connected to external PD plugged into the wall

The DFP is advertising 4 levels: 

  • 5V/3A
  • 9V/3A
  • 15V/2A
  • 20V/1.5A

My assumption was the UFP would negotiated the highest power, which is 20V/1.5A.

If I unplug/plug the DFP many times, sometimes it will the UFP will choose 20V/1.5A, but 95% of the time it will choose 5V/3A.

I have tried manually grounding the input/output, 3V3, when un-powered, looking for some external state that might effect the behavior, but nothing changes the behavior.

I need to know:

  1. Is Config 3 supposed to choose the highest power?
  2. What external factors could affect how the UFP chooses one of the advertised levels?

1 Reply

  • Hi Michael,

    Yes, you should be able to negotiate the highest power using configuration 3. I recommend reconfirming that it does choose that configuration because even a slight change in the ADCIN1 values could alter which configuration mode is chosen. One way to do this, is to connect the PD controller to the GUI and check the "Transmit Sink Capabilities" register to see if the Sink PDO's are configured properly.

    I would also recommend tying VBUS1 and VBUS2 together instead of grounding VBUS2 as it states in the datasheet.

    You mentioned that you are using a PD analyzer, could you please attach your PD logs as well? 

    Thank you,