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AM3352 with Linux and RTC only

Santhosh Ramani
Expert 2765 points
Other Parts Discussed in Thread: TPS65217, AM3352

Hello Everyone,

I'm using AM3352 with TPS65217 and would like to know if anyone has tried to run RTC-only while working with Linux. I would like to use the internal RTC, provided with an external 32 KHz crystal and a 1.8V supercap.

I'm using Rev 2.0 or higher silicon, so I'm guessing there are no additional errata's regarding RTC only mode. I also understand that the current consumption of the RTC module is around 30uA at 1.8V (got that from the wiki site).

Do I need to put the RTC in Idle mode to allow it to continue working even if rest of the system is not powered (The datasheet says that the RTC is default in smart-idle mode) ? If so, how to do the same?

Thank you for your replies.

- Santhosh

  • 0
    TI__Guru**** 393215 points
    Hi Santhosh,
     
    RTC-only mode is covered in the AM335X TRM, Rev. I, section 8.1.4.3.5. Additional information for power management (PMIC control) can be found in section 20.3.3.8.
  • 0 in reply to Biser Gatchev-XID
    TI__Guru 62855 points

    You mentioned using a 1.8 volt super cap for the RTC supply.  The RTC supply requires a regulated 1.8 volt power source.

    How do you plan to maintain a 1.710 to 1.890 volt power source with super cap?

    Regards,
    Paul

  • 0 in reply to peaves
    Expert 2765 points

    Hello Biser, Paul,

    Thank you for your replies. Yes, I did read through the TRM section 8.1.4.3.5 but to Paul's point I agree that the super cap will not work for us. We have decided to use an external RTC with super cap and not use the RTC at all.

    I do have a question regarding connecting the Wake_up and PMIC_PWR_EN signals for the TPS65217. since we are not using the RTC, according to the datasheet, I've connected the XTAL_IN to ground and left XTAL_OUT unconnected. Can I still use the Wakeup/PWR enable signals or should I just tie PWR_EN to 3.3V output from the PMIC?

    Thanks once again for your replies.

    Regards

    Santhosh

  • 0 in reply to Santhosh Ramani
    TI__Guru 62855 points

    Please read Section 3.1.7 of the AM335x Silicon Errata and the OSC1 Not Used section of the latest AM335x Data Sheet for proper connections to RTC_XTALIN.

    Regards,
    Paul

  • 0 in reply to peaves
    Expert 2765 points

    Hello Paul,

    Thank you so very much for pointing it out, I was using an old Technical Reference manual. I've read through section 3.1.7 of the Errata and section 4.2.2.5 of the data sheet. I will leave the 2 pins unconnected.

    Based on the datasheet it seems that the OSC1 is disabled by default. Does this mean that I should still be able to use the WAKE_UP, PMIC_PWR_EN signals from the RTC? Just wanted to confirm.

    Thanks once again.

    Regards

    Santhosh