AnsweredAssumed Answered

MX7 internal vs external RTC

Question asked by Lars Heinrichs on Aug 29, 2018
Latest reply on Aug 30, 2018 by Lars Heinrichs

Hello Community,

 

several months ago I have asked some questions on the RTC of the MX7:

https://community.nxp.com/message/940285
https://community.nxp.com/message/959913

 

The answers in the threads are basically:

  • Use an external RTC for lower power consumption
  • The XTALI and XTALO for the internal RTC can be connected to GND/Float if no crystal is added here
  • "External RTC may be preferable solution when it is needed to get coin cell based power during

    long time. It is very hard to create RTC with nA consumption as part of a SOC." (quote from answer in one of the threads above)

 

Now my customer had some questions on the external RTC and said "it works with the internal RTC", what threw me off, because the whole point of addind an external RTC was to save energy by not using the internal RTC at all. I checked the datasheet and it says the internal RTC will use an internal clock source if no external oscillator is present, what will draw even more energy. This is pretty much the worst case, cause it basically means the external RTC is actually not needed at all and the energy consumption is the highest possible ...

 

May I disable the internal RTC?

If not, why was using an external RTC (see quote above) recommended at all, if there is no benefit?

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