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Using TPS65910B with the AM335x - RTC & DDR3

Stephanie Goedecke
Prodigy 165 points
Other Parts Discussed in Thread: TPS65910, TPS65910A, TPS51200, TPS51206, AM3359

I'd like to use the TPS65910B to power the AM335x on a project.  Can the TPS65910B's VRTC output be used to power the AM335X's VRTC?  In the AM335x reference designs, an additional regulator is always added to power the RTC instead of using the VRTC from the TPS65910.  I'd rather not have to add an additional regulator if the one already in the PMIC will work.

Also, is there a reference design for the AM335x with the TPS65910B and DDR3?  Or are there any AM335x/DDR3 routing rules?

thanks

 

 

  • 0
    TI__Genius 16690 points

    The additional LDO and reset logics are necessary for satisfying power sequence requirements to use PMIC_PWR_EN functionality.  The power sequence is described in Figure 4-1 in the data manual. If the PMIC_PWR_EN function is not required in the system, the additional circuits can be removed.  Please refer to the note E. in Figure 4-1 for additional details.

  • 0
    TI__Genius 16690 points

    There is an issue in the reset circuit of the AM335x EVM schematic.  AM335x PWRONRSTn signal should be driven by VDDSHV6 power supply voltage level (1.8 V or 3.3 V) although it's driven by VRTC (1.8V) in the schematic. Please use VDDSHV6 voltage level for PWRONRSTn when you design your schematic.  The reset circuit will be updated for fixing the issue in next AM335x EVM schematic release. 

  • 0 in reply to kshin
    Prodigy 165 points

    Thanks. 

    Do you happen to know when the updated AM335x EVM schematic will be released?

  • 0
    TI__Genius 9190 points

    Hello Stephanie,

    for the DDr question, We will have the DDR3 guidelines in the next release of the Data Manual which will be out around 12/15/2011.

  • 0 in reply to Stephanie Goedecke
    TI__Genius 16690 points

    I don't know the exact date but it will be released soon.

    I have posted this information in your other post but I'll also post here in case the other people just look at this post. 

     

    I have been just informed that the part number for new TPS65910 device to support AM335x + DDR3 is TPS65910A3 instead of TPS65910B. The information in AM335x power solution slide and wiki articles will be updated with TPS65910A3.

     

  • 0 in reply to kshin
    Prodigy 30 points

    Thanks for the correction on the supply voltage for the reset circuitry.That will become handy.

    However, it is a bit difficult to understand the need for the external LDO. In the EVM schematics the VRTC LDO is always on when VBAT is present. So is TPS65910A VRTC output. Or am I missing something?

  • 0 in reply to Risto Holtta
    TI__Guru 68880 points

    Risto, it is more of a power sequencing issue.  VRTC is not sequenced properly and thus an external LDO is required at power on when the RTC-only feature is needed.

    Regards,

    James

  • 0 in reply to Risto Holtta
    TI__Guru 55265 points

    The EXT_WAKEUP output buffer is powered by the VDDS_RTC power domain.  This signal is what controls the TPS65910 when operating in the sleep mode where only the AM335x RTC is powered on.

     

    Therefore, you must have a separate voltage regulator to source the VDDS-RTC supply form the battery if you plan to use the EXT_WAKEUP output to control the TPS65910.

     

    Regards,

    Paul

  • 0 in reply to peaves
    Prodigy 165 points

    It sounds like the TPS65910 VDDS_RTC supply is not always powered when the VBACKUP battery is connected, but an external voltage regulator would always be powered when the battery was connected.  Therefore, a design must have an external voltage regulator to source the VDDS_RTC supply from the battery to be able to use the EXT_WAKEUP. 

    Or is this not the case?  Thanks for clarifying.

  • 0 in reply to kshin
    Prodigy 50 points

    Hi Kazunobu

    I'm also working on a design with AM335x and DDR3 SDRAM, and would like to use TPS65910A3.

    I'm pleased to see that the SWU93A is updated, so the DDR voltage can be set to 1.5V, but what about the VCtt (0.75V), do I still
    need an additional "SINK/SOURCE DDR TERMINATION REGULATOR" like the TPS51200 or TPS51206?

    http://www.ti.com/lit/ug/swcu093a/swcu093a.pdf

    Kind regards

    Peter

     

     

     

  • 0 in reply to peaves
    Prodigy 10 points

    Hi,

    It is still not clear to me, assuming that I want to use the AM335x
    internal RTC and there is a power failure.

    The AM335x RTC voltage domain should be powered by the Battery (Li) connected
    to the 65910A, however if I will use the external LDO instead there will be no
    power supplied to the AM335x.

    How should I connect the VRTC if I want the AM335x RTC zone to operate
    from the battery in case of power fail?

     

    Thanks

    Noam

  • 0 in reply to peaves
    Prodigy 140 points

    EXT_WAKEUP in AM3359 is a input, isn't it?