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AM335x Schematic Checklist RTC signals

Prad1
Genius 3825 points

Hi,

There seems to be some mistake in the Schematic Checklist regarding the RTC connections.
The "If RTC internal oscillator is not used" sections says if the "The internal RTC is not used at all"
"connect OSC1_IN and VSS_RTC to PCB ground" and I think it should be modified as "OSC1_IN to NC".

And in our case we don't use the internal RTC feature but we need
PMIC_PWR_EN to enable the power supply.
but the checklist says "PMIC_PWR_EN needs VSS_RTC if you use it to enable the power supply"
could you please let us know how exactly should the VSS_RTC pin be connected in this case.
will it be ok to connect VSS_RTC to PCB ground?

Best Regards.
prad.

  • 0
    TI__Guru**** 393215 points
    Hi Prad,
     
    Please refer to the latest AM335X Datasheet, Rev.E, section 4.2.2.5. This is the latest and confirmed correct source of information.
     
    1. OSC1_IN should be NC.
    2. If RTC isn't used VSS_RTC should be connected to GND. This doen't concern PMIC_PWR_EN.
  • 0 in reply to Biser Gatchev-XID
    TI__Guru 63125 points

    The AM335x Schematic Checklist comment "Note that PMIC_PWR_EN needs VSS_RTC if you use it to enable the power supply" was not added by a TI employee and it is not an accurate statement.

    The AM335x VSS_RTC terminal is only available on the ZCZ package option and the primary purpose for this terminal is to provide a Kelvin ground to the crystal oscillator circuit when using the ZCZ package.

    The recommended connection of the RTC_XTALIN terminal has changed since this information was orgiginally added to the checklist.  We determined this oscillator has a internal pull-up resistor when disabled so the data sheet was updated with the new recommendation, but the schematic checklist was never updated.

    I have corrected this on the schematic checklist.  Please review it and let me know if you see any other issues.

    Regards,
    Paul