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PMIC TPS65910AA1 (VRTC) supply connection to AM3352 VDDS_RTC

Manoj Agarwal
Expert 1030 points
Other Parts Discussed in Thread: AM3352

Hi,

I am connecting TPS65910AA1 (VRTC) supply output to AM3352 VDDS_RTC input for RTC supply of MPU. Please let me know if this is correct or not as in TPS65910Ax user guide  for AM335x external LDO connection is shown. Is there any reason why we can not take VRTC supply from PMIC to provide supply input to AM335x RTC supply VDDS_RTC.

Regards

Manoj A

  • 0
    TI__Genius 10885 points
    You may run into issues connecting VRTC directly to VDDS_RTC for the TPS65910AA1, as the TPS65910AA1 has VRTC configured with a current limit of ~100µA while in OFF and BACKUP mode. When power is first introduced, the device transitions from a NO-SUPPLY state to an OFF state before it can transition to an ACTIVE state. If the RTC of the AM3352 attempts to draw more than ~100µA during this time the rail may not be able to regulate at 1.8V. Unfortunately, if this rail is not allowed to regulate properly the PMIC will not be allowed to boot, and so it is often recommended to use an external buck for the RTC for this particular spin.
  • 0 in reply to Richard Solarski
    Expert 1030 points

    Hi Richard,

    Thanks for your reply.

    Can we connect any other supply of AM3352 supply to VDDS_RTC of AM3352, like VAUX1, VPLL, VIO, VDIG1,VDIG2,VDAC. We want to use RTC in

    RTC timer functionality. I am referring AM335X schematic checklist , page no 6.

     

    As per AM335X checklist for RTC timer functionality , We needn't to connect PMIC_POWER_EN to PMIC PWRHOLD pin. Please confirm.


    Also As per AM335X checklist for RTC timer functionality, RTC_PWRONRSTn should be connected to 1.8VPWRONRST. I am using 3.3V at PMIC VDDIO so in that case how to connect these two reset.

    It would be better if you provide refernec schematic where PMIC TPS65910AA1 is used with AM335X in RTC time functionality mode.

     

    Thanks

    Manoj A

  • 0 in reply to Manoj Agarwal
    TI__Genius 10885 points

    Hi Manoj,

    VDDS_RTC should be near 1.8V, and should be connected to a rail that will remain active as long as RTC functionality is needed. This may vary depending on any one specific application.

     

    The PWRHOLD feature of the PMIC holds keeps the PMIC active for as long as it is asserted high. When this pin goes low, the PMIC can shut down and all the rails will turn off except for the VRTC LDO, which will have a limited current output of ~100uA.

     

    For the RTC_PWRONRESTn, the AM335x Starter kit uses a logic gate in the VRTC LDO domain to control this pin,

  • 0 in reply to Richard Solarski
    Expert 1030 points
    As we are using RTC in RTC timer functionality but no RTC only mode and as per AM335X schematic checklist we are not using PWRHOLD pin. Please let me know if we can leave PWRHOLD pin NC and it is safe to do so.
  • 0 in reply to Manoj Agarwal
    TI__Genius 10885 points

    Hi Manoj,

    The PMIC will shut down automatically after a start-up event unless PWRHOLD is held high, or DEV_ON is set to 1 over i2c, within 984ms of NRESPWRON being released. This is mentioned a few times within section 5.2.2 of the datasheet, and how one asserts PWRHOLD depends on their conditions. If the device should just turn on with input PWR, PWRHOLD can be tied to VRTC. If external control is required, an external GPIO or Power-good can set this pin as well.