How can we maintain RTC in WP76xx without VBAT

The WP76 series doesn’t have an BAT_RTC pin compared to WP8548.
How can we maintain the RTC if we don’t use an external battery and charger circuit?

Hi,

Not sure what you mean, pin 21 is BAT_RTC for the WPx5 and the WP76 families, the WPx5 family can charge the cap where the WP76 can’t so you just need to put a precharged a coin cell in place and the unit will draw on this when VBATT is not available.

Regards

Matt

Hi,

the Product Technical Specification of WP8548 describes the internal RTC as below:
“The AirPrime WP75xx/AirPrime WP8548 module‘s internal RTC is powered from the VBAT_BB supply (when available).
The module also provides an interface (BAT_RTC) for using a coin cell to maintain the internal RTC when VBAT_BB is removed from the module.”

The WP76 specification doesn’t mention that there is an internal RTC and does not say that we can connect a coin cell.
The definition of pin 21 says “Reserved - No connection”.

Did you get your information from another specification?

Greetings,
annaertd

Annaertd,

I was looking at old documentation, the latest PTS and scaleability guide do indeed not show an external supply on pin 21. So I guess its Vbatt or you lose the RTC.

Regards

Matt