PCF2127T: Vbat and VDD power on sequence confirmation

[TCL_1]

hello,

In the application note AN11266 of RTC chip PCF2127T, I found an additional requirement about Vbat and VDD power supplies, in section 5.2:

a backup battery can be attached to the VBAT pin to enable the battery switch-over
when the main power VDD fails. If VBAT is not used, it has to be connected to ground. If
VBAT is used, one of the supplies (VBAT or VDD) has to be turned on before the other

Does it required the Vbat and VDD can't power up simultaneously? What's the interval required?

It's looks strange and I didn't found same requirement in PCF2127T's datasheet. Thanks advance for your review and confirmation!

Best Regards

TC Liu

[TomasVaverka · Accepted solution]

Hello Tyrone,

First off, sorry for this delayed response.

Vbat and VDD can be powered up simultaneously if Vbat is used in application.

The sentence was trying to highlight that either one of power supply will have to be available to get system working, but both power supply (Vbat and VDD) can be powered up simultaneously with no issue.

Best regards,

Tomas