UCPD (USB-PD) use DBCC pins for something else if dead-battery not needed?

[Erlkoenig]

Hi,

i am using STM32G0B1KB and the UCPD peripherals to implement an USB-PD device with 2 ports:

- Port 1 is DRP
- Port 2 is Source only

I need the dead battery pulldowns for port 1, so I will connect the UCPD1_DBCCx pins with the UCPD1_CCx pins as described in the manual. However, for port 2 I don't need to present the dead battery pull-downs - when the MCU is unpowered (dead battery) and the user connects some other device (e.g. smartphone) to port 2, simply nothing should happen. The manual states:

> If dead battery behavior is not required (for example for source only products), then UCPDx_DBCC1 and UCPDx_DBCC2 pins must both be tied to ground.

What resistance can be used to connect those pins to ground? Since I don't have any pins left, can I instead use the DBCC pins for something entirely different? E.g. connect LEDs (to GND) or some other digital output with a weak external pull-down resistor (e.g. 10kOhm)? Will this prevent the MCU from enabling the pull-downs?

Thanks!

[MROUV.1 · Accepted solution]

Hello,

 TCPP protection devices (TCPP01-M12 or TCPP03-M20) handle dead battery (DB) signaling even when there's no power, making direct connections between UCPD1_DBCCx and UCPD1_CCx useless.

Thus, the pins typically used for UCPD1_DBCCx can be repurposed as GPIO for additional functionalities (LED as exemple).

Best regards,
Mathieu

[Erlkoenig]

Great to know, thank you very much!

[Tranzorb]

Hello all,

I am reading your answer, and except if I misread it seems your AN5225 says the opposite, see pages 27 to 30 : the DBCCx pins must be connected to the CC pins of the MCU when used with a TCPP with dead battery enabled. Table 12 on page 30 is particularly explicit.

Please review your answer accordingly or correct your documentation if the documentation is wrong.

Thank you,

Best regards,

Frederic