PA0 and PC13 wakeups

[coloradocarlos]

The schematic checklist recommends to add test points to PA0/PMIC_INTN and PC13/PMIC_WAKEUP.

Can these pins be used for other features? Our company is interested in a “wake up on LAN” type of feature to externally trigger PC13 to power up the board when the PMIC is powered off.

[Neeraj Dantu]

Carlos,

If the PMIC is in OFF state and the SoC is not powered, please take a look at PMIC_PONKEYn pin as it is one of the turn-on inputs as listed in section 5.4.2 of the PMIC datasheet(https://www.st.com/resource/en/datasheet/stpmic1.pdf).

Best,

Neeraj

[coloradocarlos]

We reviewed using the line in PMIC_PONKEYn and decided that there is some risk in using it. The PONKEYn is not only used for power on but for shutdown too. A spurious signal could cause the board to shutdown unexpectedly.

To be more specific, PC13 can be the RTCOUT1 output during VBAT mode (I found you need to set the right bits in RTC_CR). This could complicate using PC13 for external events to trigger a wakeup. Given this background, is PC13 a supported input or is it considered “for internal use only”?

[Neeraj Dantu]

Carlos,

Since PC13 is connected to PMIC_WAKEUP, any wakeup signal that is intended for the PMIC will also go into PC13 back feeding current if VDD is not powered up. However, PC13 is part of VBAT domain. So, if you use an external battery to power VBAT, you should be able to assert a signal on this pin without any back current. So, if you are planning to use VBAT or can keep VDD on, you should be able to use PC13/PMIC_WAKEUP externally.

Best,

Neeraj

[Author]

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