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UCPD and DBCC (dead battery) doubts

Senior III

According to RM0456, p. 3459


So in addition to CCx pins also PB5 and PB14 (DBCCx) cannot be used. The above does not make much sense to me. I imagine (only imagine) that internally DBCC support is implemented like shown below and for "dead battery" to work DBCC pins have to be connected with respective CC pins. That makes sense. But why DBCC pins have to tied to ground when "dead battery" support is NOT required? I see no explanation for that.
Is the documentation correct with that respect? Could anyone confirm/explain?
The problem here is that I need UCPD but do NOT need DBCC (power source only config) and I would to use PB5 and PB14 pins (DBCCx) for their other functions while according to RM0456 I cannot.




ST Employee


You can use the Pins if well programmed out of reset to their corresponding mode. Here is a discussion on similar use case but not using UCPD features :

hope it helps you ,


Hi @STOne-32,
Thank you. RM0456 states: "If dead battery behavior is not required, [DBCCx] pins must both be tied to ground". So, are you saying this is not exactly the case? Would you say this RM0456 topic should be revised?

Where do you have that diagram from? IMO it's incorrect: the 5k1 pulldown is on the CC pins and DBCC pins steer the switches which connect it to to the CC pins.

The above sentence, while it may be rephrased to be less imperative, is more in the sprit of "consequences of ungrounded DBCC may be surprising and relatively hard to explain, so better make users ground it".


Cześć Jan, I drew this diagram myself. I only guess it is how DBCC works and I admit, this diagram can be completely incorrect. Some clarification from those who know for fact would be much welcomed.


Senior III

Hi @STOne-32, would you care to comment?