topic Re: MX7 internal vs external RTC in i.MX Processors

MX7 internal vs external RTC

demoniacmilk — Wed, 29 Aug 2018 15:38:12 GMT

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?

Re: MX7 internal vs external RTC

Yuri — Thu, 30 Aug 2018 06:35:20 GMT

Hello,

Using an external RTC allows to fully power off i.MX7 - this is main advantage here.

Have a great day,

Yuri

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Re: MX7 internal vs external RTC

demoniacmilk — Thu, 30 Aug 2018 07:46:00 GMT

Im using the MX7 with a PF3000. A LiCell is connected to the PF3000 that supplies the RTC as well.

To fully power off the MX7, I probably have to disconnect the PF3000 from the LiCell and connect the cell to the RTC only?

Re: MX7 internal vs external RTC

demoniacmilk — Wed, 12 Dec 2018 14:57:55 GMT

is this correct?
is there any way to keep the tamper pins active without the internal RTC being active?