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i.mx28 RTC backup current on 24MHz Xtal

Question asked by Ruud Commandeur on Jun 9, 2015
Latest reply on Jun 11, 2015 by markwilliams

Hi Everyone,

 

As the title says: I'd like to know what the typical current would be when the i.mx28 is in RTC backup mode when running on the 24 MHz Xtal. The idea is, that when the (5V) power is removed, that the battery connection is backed up by a goldcap as can be found in schematics as "Optional RTC backup". However: we do only have a 24 MHz Xtal and no 32.768 KHz Xtal. With the 24MHz RTC persistent bit in the hw_rtc_persistent0 register I did manage to keep the 24 MHz Xtal active when 5V power is removed and the RTC indeed keeps running.

 

However, this only lasts for a couple of minutes, since the goldcap voltage drops quite fast. I know that the typical RTC backup curent is about 13,5 uA but that is for running on the 32.768 KHz Xtal. Is there any known value for the 24 MHz operation in this mode?

 

Regards,

 

Ruud

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