RTC not working when External supply 2.5V direct to PMIC_BBAT

Hi,
I do one experiment on Jetson Orin Nano for RTC , seem like when I supply external power supply 2.5V direct to the PMIC_BBAT pin and set the RTC . After plug/unplug the system like the RTC still working .

However, when I leave it 24hours ( 1 days ), the RTC time is back to the 1970 after plug back the system.

image

based on datasheet of Jetson Orin Nano, the input PMIC BBAT will support 1.8V for minimum right ? . But for my case 2.5V is already not support , can I know any setting that needed ?

Are you saying that if you just power off the board for a while and then reboot, then RTC time is still correct but if you leave the board for long enough, then it will go back to 1970-01-01?

Yes , correct after I leave a board for 1 days . It happen on 2.5V.

Is it possible to know how long it took to make this issue happened?

above 12 hours.

Is it still 2.5V after 12 hours? Basically, RTC time will be restored only when power supply is under limit or removed.

yes, still 2.5V.

Did you check your board to confirm below components (R222, R560) are mounted?


image

Yes, already confirm the components are mounted.

That’s weird. Did you test how long the time can be kept for? Or you can also try a DC power supply with 2.5V to check if it is battery issue.

yes, I test also on 2h and 4h it still working but when leave it for next day , the rtc time back to 1970 .

I already try with DC power supply , for next day rtc time still back to 1970.

I also insert this command : $ zcat /proc/config.gz | grep CONFIG_RTC_HCTOSYS_DEVICE
output is : CONFIG_RTC_HCTOSYS_DEVICE=“rtc1”

However I already modified dev file to rtc0 : /dev/rtc → rtc0

It is due to not update kernel config?

What jetpack release are you using?

What do you mean “plug/unplug the sytem”? Have you try to plug out main power supply and after a day plug in and power on system to check the RTC time?

In addition, could you share a photo of your board to make sure no problem on board setting?

I used my custom board but for the RTC connection , I using the same circuit like u share previously.


for this one, yes I already try it , RTC fallback to 1970 after I leave it overnight.

There is no update from you for a period, assuming this is not an issue anymore.
Hence, we are closing this topic. If need further support, please open a new one.
Thanks

Is this still an issue to support? Any result can be shared?