TPS26750EVM: Source only mode, Sink pulsing between 5V and ~18V in PPS mode

Hi Joel,

Thank you for your inquiry. Our device expert will respond shortly.

Hi Joel,

Unfortunately, I am unable to access Google Docs files. Could you please attach the files directly to this thread?

Regards,

Conner

Hi Conner,

i've attached the files:
USB-C PD TPS26750-20250203T130344Z-001.zip

Thank you Joel, I will review these today and provide you an update EOB.

Regards,

Conner

I won't be able to complete my analysis until tomorrow EOB at the earliest. My apologies for the delay Joel.

Hey Conner,
Is there an update available?

The sink is requesting 5V PPS then 18V PPS, alternating. It's possible that your sink is sensing VBUS, seeing a voltage drop on VBUS below a set threshold when ramping up the load, and then requesting 5V PPS. However, all of this behavior is being driven by the sink.

Regards,

Conner

I've already compared the voltage drops between the different chargers and the successful and unsuccessful PPS-Charging with the TPS26750-EVM, and to be honest i can't seem to find a pattern. 
I know that the PPS voltage request are controlled by the sink, but it just seems weird, that every other PPS source that I've tried (must've been at least a dozen since i got this phone) doesn't show this behavior, so there has to be something different with the TPS26750EVM. 
Is there a way to prevent the voltage from falling under the suspected threshold, like offsetting the voltage or something like that?

TI US is closed today, sorry for delays. 

Hi Joel, 

Taking over support on this thread from Conner, can you elaborate what kind of phone are you testing with and have you tested with other phones with PPS sink capability? 

Also I noticed in your config, Source PDO 5 for PPS is set to be in between 3.3V to 21V. The minimum PPS voltage supported on TPS26750 is 5V according to PD spec, can you try changing the minimum voltage [167:160] and see if the results change? 

Thanks and Regards,
Raymond Lin

The problem appears when i test with a "Nothing Phone (2)". With all the other phones I've tested so far, there are no issues, and the PPS charging works on the first try. As already said, the PPS charging with the "Nothing Phone (2)" works sometimes, about 10-20%. 

I've changed the minimum voltage for PPS in PDO 5 to 5V, which didn't make a difference. I have other USB PD power supplies, which also supply 3.3V-21V, so i didn't expect this to make a difference. 

Of course, it would be easy to say now, that since this problem only appears with this specific phone, that its entirely the phones fault. But since the problem never appears with other chargers, there has to be something different with this one, which makes the phones USB-PD state machines act up. Do you see any other difference?

Hi Joel, 

Looks like Conner mentioned this previously as well but it looks like the "Nothing Phone (2)" is behaving abnormally when bouncing back and forth between requesting 5V and 16V (all PPS PDO). 

You mentioned this phone works about 10-20% of the time, were there any significant difference between the passing and failing test scenarios? For example, was the phone battery low or was it being used? Can you also provide the phone manufacturer and model information?

With other PD source (not TPS26750), did this issue not happen at all whatsoever? It seems very strange to me that this particular phone is exhibiting such a behavior, have you tested with other PPS capable phone and see if any of those devices request the same abnormal PPS pdos? 

From the logs you provided, the sink (Nothing Phone (2)) is the one driving the request and from TPS26750 (source) perspective, it's job as the PD source is to Accept the sink's request and deliver the power which is what it's doing.

Thanks and Regards,

Raymond Lin