We are facing a drift in RTC of the Processor

[vikassingh]

Hi Team,

In processor, "MK70FN1M0VMJ12" we are facing a clock drift in RTC during both Power on and Power off condition. During Power off, a coin battery(CR2032) is used as power source. Also this drift is not constant. It is varying. Operating temperature is within range of 20 deg Celsius to 35 deg Celsius. Maximum drift of 12 seconds per day is observed. I had attached RTC and crystal section of our schematic. Please help us further in resolving this issue. Is compensation register usage solves this issue? Please help as ASAP.

[Hui_Ma]

Hi,

From K70 reference manual, please refer below RTC crystal circuit design:

TWR-K70F120M board also using the same connection:

About RTC compensation, please refer application note AN4949 for the detailed info.

Wish it helps.

Have a great day,
Mike

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[vikassingh]

For more details I am adding RTC Calculation also.

	Crystal Part Number	ABS07-32.768KHZ-7-T
	Temperature Coefficient	-0.036 ppm/˚C
S.No.	Operating Temerature (˚C)	Crystal Frequency Error (PPM)	Error/Day (Seconds/day)
1	-40	-152.1	-13.14144
2	-30	-108.9	-9.40896
3	-20	-72.9	-6.29856
4	-10	-44.1	-3.81024
5	0	-22.5	-1.944
6	10	-8.1	-0.69984
7	20	-0.9	-0.07776
8	25	0	0
9	30	-0.9	-0.07776
10	40	-8.1	-0.69984
11	50	-22.5	-1.944
12	60	-44.1	-3.81024
13	70	-72.9	-6.29856
14	80	-108.9	-9.40896
15	85	-129.6	-11.19744