Can Real Time Clock count even if BMS is off

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Can Real Time Clock count even if BMS is off

Contributor II


This is Baran Celikten from Ford OTOSAN BMS team.

We are using SK32K144EVB and FRDM33771BSPIEVB cards to develop BMS algorithms. We have some modes which includes sleep or even off mode ( when supply voltage is lower than a threshold). At this point, when BMS is off or sleep, we need to time clocking. Is it possible for this cards even if supply voltage is not enough. Or in other words, Is voltage sensing enough for RTC feature and store clock to use when BMS is on.


Baran Celikten

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NXP Employee
NXP Employee


I am not sure If I got the question right.

Basically, what I understand is that you are trying to measure time intervals, as long as the MC33772 is in sleep or completely off due to the undervoltage scenario, using the RTC timer on the S32K144.

If my understanding is correct, the S32K144 has to be still powered up, even if the MC33771 is not. So, according to the S32K Data Sheet the voltage has to be at least 2.7V in order to still use the RTC timer.


More than that, the RTC is Fully Functional in all the Power Running Modes of S32K.pastedImage_3.png

I hope this answers your question. If not, please detail a bit your scenario :smileygrin:.

Hope this helps,


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Contributor II

Thanks mariuslucianandrei,

You are right about my question but,

I'm a bit confused and have new question :smileygrin:. So, if cell voltage is not going below 2.7, it will be always power mode unless battery has some capacity.

It creates another wish for us which can be named "intentional power off mode".

In other words, I don't want to lose my cell capacity for BMS complex calculations in all the time, but lower complex functions like RTC should work to calculate the power off mode duration. Is it possible?

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