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PMIC Questions

RUSS PRITCHETT
Prodigy 90 points
Other Parts Discussed in Thread: TPS65910A

I'm working on a design for a client that modifies the TMDSSK3358 evaluation board. 

1. Our system will convert  +24V supply to +5V to provide the equivalent of VBAT on the schematics. We would like the system to power up with out user intervention with the push button.

I saw the post (http://e2e.ti.com/support/arm/sitara_arm/f/791/t/235319.aspx) which describes a method of converting the eval board to automatic start (no push button). Essentially VBAT is connected to the PWRHOLD pin of the PMIC (TPS65910A3). 

This method could be used in our system; but studying the documentation for the PMIC and AM335x, it seems preferable to use the AM335x PMIC_POWER_EN output  to drive the PMIC PWRHOLD pin & initiate a "startup reason" for the PMIC power supplies.

Is it correct that this would make the push button on the PMIC PWRON pin unnecessary?

Is it a problem that PMIC_POWER_EN only reaches VRTC of 1.8V?

2. On the TMDSSK3358 schematic, the PMIC GPIO_CKSYNC pin is pulled up to VRTC. It seems that this pin should be pulled to the VDDIO selection (VAUX33).

Am I missing something?

Thanks for your time,

Russ

  • 0
    TI__Guru**** 393215 points
    Hi Russ,
     
    RUSS PRITCHETT said:

    This method could be used in our system; but studying the documentation for the PMIC and AM335x, it seems preferable to use the AM335x PMIC_POWER_EN output  to drive the PMIC PWRHOLD pin & initiate a "startup reason" for the PMIC power supplies.

    Is it correct that this would make the push button on the PMIC PWRON pin unnecessary?

     
    Yes, this is correct. You can check the GP EVM schematics. That's how it's done there (http://processors.wiki.ti.com/index.php/AM335x_General_Purpose_EVM_Board_Design_Files)
     
    RUSS PRITCHETT said:

    Is it a problem that PMIC_POWER_EN only reaches VRTC of 1.8V?

     
    No, PMIC PWRHOLD input has a VIH treshold of 1.3V (TPS65910A datasheet, page 8)
     
    RUSS PRITCHETT said:

    2. On the TMDSSK3358 schematic, the PMIC GPIO_CKSYNC pin is pulled up to VRTC. It seems that this pin should be pulled to the VDDIO selection (VAUX33).

    Am I missing something?

     
    GPIO_CKSYNC can be left NC (see EVM schematics above).