IMXRT 1024 RTC running faster than expected

[Punithintelli]

Hello All,

I am using IMXRT 1024 microcontroller and having a issue with RTC.

To begin with we are using SNVS_lp_srtc example program provided in SDK example. RTC time is running faster than the real time value. The result is same for both Internal RC oscillator and external crystal oscillator(32.768Khz).

Thanks,

Punith P 

[RaRo]

Hello @Punithintelli,

Could you please tell us if you are using an NXP EVK or a custom board? If is a custom board, could you please give us more information about your SNVS and RTC design?

Which MCUXpresso IDE and SDK version are you using? Have you made changes to the example? Is this behavior happening from the start of operation or after a certain time had passed? Also, how much timing difference are you getting?

Finally, in which boot mode are you testing the example? Could you please test it with QSPI Flash boot mode?

Best regards, Raul.

[Punithintelli]

Hi @RaRo 

We are using the custom board and I have attached the snapshot of the SNVS and RTC design.
MCUXpresso IDE Version - 11.7.1
1024 SDK version - 2.13.0
No code changes expect adding a additional printf statements for verification.
The behavior is observerd from the start.
When the code is configured to run using external crystal(32.768khz), for 1s real time we get 1.2sec in IMxRT1024.
When the code is configured to run using internal RC oscillator, for 1s real time we get 1.5sec in IMxRT1024.
We are running it in QSPI Flash boot mode.

Thanks,
Punith P

[RaRo]

Hello @Punithintelli,

Comparing your SNVS design to the Hardware Development Guide for the MIMXRT1020 Processor, we found out that you are using an extra capacitor of 4.7uF(C40). Look at the following Power supply decoupling recommendations:

[MIMXRT1020HFUG. Chapter 3. Power supply. Table 2. Power supply decoupling recommendations]

Could you please remove the C40 capacitor of the VDD_SNVS_IN signal?

Let us know if this solves your problem.

Best regards, Raul.