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AM335x PMIC supply sequencing with RTC feature disabled.

Mark Norman
Prodigy 235 points
Other Parts Discussed in Thread: TPS65910, AM3352, TPS65910A

Hi All,

We are currently designing a system using an AM3352 with the TPS65910 PMIC.  We do not require the RTC-only low power mode of the AM3352 and are not planning to include an RTC crystal.

SPRS717 Figure 4-5 indicates that the PMIC_POWER_EN output is not available when the RTC feature is disabled.  From what I have seen, all the reference designs appear to use the PMIC_POWER_EN signal to trigger the PMIC to power on the MPU.  If the PMIC_POWER_EN output is not available, is there a recommended way to signal to the PMIC to power on the AM3352 or can the PWRHOLD signal of the PMIC simply be pulled-up permanently?

Kind Regards

Mark

  • 0
    Guru 24520 points

    Hi Community member,

    Our customer also think to be planning to not include an RTC crystal and be using an AM3352 and TPS65910A.
    Would you please comment for Mark's question?

    Best regards,
    Kaka

  • 0 in reply to Kaka
    TI__Guru**** 393215 points

    See this wiki: http://processors.wiki.ti.com/index.php/AM335x_Schematic_Checklist#If_RTC_internal_oscillator_is_not_used...

    And also: http://processors.wiki.ti.com/index.php/AM335x_Schematic_Checklist#RTC

  • 0 in reply to Biser Gatchev-XID
    Guru 24520 points

    This wiki did not answer for my question.

    I have checked those URLs before I posted this, however it do not explain how to treat PWRHOLD signal of the PMIC.

    In my understanding, PMIC need to input the enabled signal to PWRHOLD in order to supply power domains except for VRTC domain for AM335x.

    Please advice in this point of view.

    Best regards.

    Kaka

  • 0 in reply to Kaka
    TI__Guru**** 393215 points

    You can tie the PWRHOLD signal to the input power supply. If it is higher than +5.5V a resistive divider will need to be used. In this mode the PMIC will start immediately when power is applied.

  • 0 in reply to Biser Gatchev-XID
    Guru 24520 points

    Thank you for your response. 

    My question is cleared.  In addition to my previous post, would you please answer for the following question?

    [Question]

    It seems that the Stater kit of AM335x did not connect the PMIC_POWER_EN pin to PMIC. And PWHOLD pin of PMIC is connected to VAUX33. I think that PMIC need to input enabled signal to PWHOLD pin in order to supply power such VAUX33.  So, if use the Stater kit's schematic, PMIC will not start.

    I do not understand why the PMIC will start without enabled PWHOLD pin. How do start the PMIC without inputting enabled signal to PWHOLD in case of Starter KIT?

    best regards.

    Kaka

  • 0 in reply to Kaka
    TI__Guru**** 393215 points

    The Starter Kit starts up only with a PWRON pushbutton. There have been people who have modified their SK to start up directly when power is applied. This is done by moving the PWRHOLD signal from VAUX33 to VBAT, with a resistive divider.

  • 0 in reply to Biser Gatchev-XID
    Guru 24520 points

    Hi Biser,

    Thank you for your response.

    My question was cleared.

    Best regards,

    Kaka