Reinhard Meyer

GoldCap on Battery Pin to power just the RTC?

Discussion created by Reinhard Meyer on Jul 5, 2011

Reading Chapter 11 (Power Supply) I don't really get a feeling whether it should be possible to use a GoldCap (say 1 Farad) at the Battery pin - just to power the RTC for a few hours when VDD5V is not available.


It should be possible when using the linear regulators or the DC/DC using the VDD4P2 path.


The GoldCap itself has roughly 100 Ohms of internal resistance, so any switchover event resulting in a larger current from the Battery pin might bring the voltage low enough to trigger a problem.


Is it possible that such a brief current surge can happen on the Battery pin, for example when VDD5V is suddenly lost?


Considering the rather large current on the Battery pin during off state (13.5 typ/30 max) uA, a GoldCap solution might not be the best anyway, but in our typical applications a loss of VDD5V is not the operational case; or if, it is usually brief; or if enduring, a loss of time is acceptable.


Best Regards,