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MSP430F6777A: Power supply to RTC_C at LPM3.5

DDdoor
Expert 2180 points
Part Number: MSP430F6777A

Hello,

The MSC430F6777A RTC_C RTC is listed as available with LPM 3.5.

It is written that the regulator will be disabled in LPM 3.5. What route does power to the RTC follow if it does not use auxiliary power?


Best regards,
DDdoor

  • 0
    TI__Mastermind 26380 points

    Hey DDdoor,

    The RTC must be powered through AUXVCC3 as it is part of the Backup Subsystem.  Externally, It can either be powered independently or it can be connected to VDSYS externally.  If you connect a capacitor to AUXVCC3, there is a built-in "charger" you can use to recharge it when DVCC returns.  

    Thanks,

    JD

  • 0 in reply to JD Crutchfield
    Expert 2180 points

    Hello JD,

    Thank you for your reply.

    It seems that the MSP430F6777A does not have a VBAT pin.
    There is the following in the user guide(slau208q).
    Is this possible?

    3.1 Battery Backup Introduction

    NOTE: Operation without separate battery backup supply
    If there is no separate battery backup supply in the system, connect the VBAT pin to DVCC
    and set bit BAKDIS=1.

    Best regards,
    DDdoor

  • 0 in reply to DDdoor
    TI__Mastermind 26380 points

    Hey DDdoor, 

    There is not an external Vbat pin, but AUXVCC3 connects to an internal Vbak as shown in the image you provided above.  

    If you search "backup" in the datasheet, you will discussed a bunch.  In fact, if you look at table 5-19 you can see the current draw on AUXVCC3 with the RTC enabled and disabled.  https://www.ti.com/lit/ds/symlink/msp430f6777a.pdf?ts=1591318184104 

    Thanks,

    JD

  • 0 in reply to JD Crutchfield
    Expert 2180 points

    Hello JD,

    The Battery Backup System in the user guide (salu208q) is not written about RTC_C, so I would like to confirm.

    NOTE: Operation without separate battery backup supply
    If there is no separate battery backup supply in the system, connect the VBAT pin to DVCC
    and set bit BAKDIS=1.

    When doing the above with RTC_C of MSP430F6777A, should I replace VBAT with AUXVCC3? And
    Should I set BAKDIS=1?
    By doing this, is it possible to support Operation without separate battery backup supply?

    Best regards,
    DDdoor

  • 0 in reply to DDdoor
    TI__Mastermind 26380 points

    Hey DDdoor,

    Sorry for the confusion on the naming, but the "Battery Backup" system section is only for devices with RTC_B and does not apply here. Not all features in the Family User's Guide apply to every device in the family.  The MSP430F6777A does not have the "battery backup" functionality.  There is not a BAKDIS bit or a BAKCTL register in the MSP430F6777A device.  

    The MSP430F6777A has the AUX module, and the pin that you care about is AUXVCC3.  Chapter 4 of the Family User's Guide describes it's functionality.  The Note in Section 4.1 explains how to connect the AUXVCC3 pin. Take a look and see if the functionality is clear.  

    Additional to that note, for customers using AUXVCC1 as a secondary supply source you can connect AUXVCC3 externally to VDSYS so that it runs off of the secondary supply in the case that DVCC is lost.  

    Sorry once again for the confusion.  Hopefully, this clears up the question.  

    Thanks,

    JD

  • 0 in reply to JD Crutchfield
    Expert 2180 points

    Hello JD,

    Thank you for your answer.
    I understand.

    Best regards,
    DDdoor

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