RTC Boot Issue with Jetson Nano

Hi,

We are having an issue with Jetson Nano processors and need a technical support on this. The issue is as below:

In our custom board, when RTC battery is connected, the processor randomly not boots. Bootloader is not even initiated in this case. When RTC is disconnected, everything works fine all the time. Our connection order is “2032 RTC battery – SS34FA diode – Jetson BBAT pin”. Below are the list of additional findings during our investigation:

• We found out that the issue is not directly related to RTC battery connection. It always boots fine if RTC battery voltage is applied for the first time. It seems that issue occurs after Jetson starts to keep time data.
• After it runs for the first time, if battery voltage keeps connected, we can observe the issue in consecutive power-ups. (Not %100 but around %70-80 of the time)
• The issue is not happening with older production Jetson Nano processors. We have ones with 2019 production date and they work fine. The issue occurs with the one with 2022 date and with 2023 date.
• The issue is not happening with Xavier NX processors.
• Changing battery, diode, providing stable RTC voltage from power supply (everything related to RTC side) did not make an impact on the issue.
• We tried different JetPacks 4.6.1 and 4.6.4 to see if that made an impact but it didn’t.
• We checked the power-up timings when this occurs, but everything seems normal. Reset signal also goes high for a brief period but then goes low again.
• We are stuck in the current situation. We suspect if this may be related to PMIC MAX77620 in Jetson, which handles this RTC and power up sequence things, but we don’t have any information on that side and how time data can prevent SoM from booting.

Any help would be much appreciated.

Hi,

Will this happen on a DevKit?

Does serial console show anything?

Hi,

It’s not happening on the DevKit. Nothing is printed on the serial console when this issue happens.

If you remove the RTC battery then it always boots fine?
Can you provided the serial number of modules that work and don’t work?

Yes, without RTC it always works. Serial numbers are as below:

  1. 1424723005397 / 4023 (Not working)
  2. ⁠1424221068615 / 2221 (Not working)
  3. ⁠1423419001399 / 2819 (Working)
  4. ⁠1423119049750 / 2819 (Working)

Can all these Jetson Nano modules work fine on devkit with RTC battery?

Yes, they all work fine there with RTC.

So it is not module issue. It is hard to tell where the issue is, but you may need to check your carrier board design and compare to the reference (P3449) schematic to find out root cause.

Yes we can’t say it’s a module issue directly but we are hoping to get some suggestions on what may be causing this. Without RTC everything works perfect. RTC connection is pretty simple and we are following NVIDIA guidelines there. Power-up timings are also fine when RTC is connected. We are never having this issue with Xavier NX modules or older Jetson Nano modules. Maybe this different behaviour with different SOMs can help finding the issue.

I don’t think it is RTC part issue. It is hard to tell what caused this. It might be some other interfaces issue. As said you can check your design based on checklist sheet in DG and the reference schematic