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AM335x : question about RTC-only mode

Devin Park
Expert 5965 points


Hi,

We want to implement RTC-only mode , which means to turn off all the module of the system such as DDR, NAND Flash, PMIC, etc., only except RTC module in AM335x. it's because we hope very low power consumption.

Please check if my understand is correct.

Then if we turn off Power** for PMIC abruptly, Does AM335x enter into RTC-only mode autommatically?(suppost that VDD_RTC is still supplied by BAT ).

And then the system should wake up from RTC-only mode. For it, we need a triger via the ext-wakeup0.

But before giving the triger using the ext_wakeup0,  PMIC should be powered. Actually, it will not work because the pmic_pwer_enable pin is LOW, is it right?

So I'm thinking following sequences for wake-up.  Please review it.

1) suppling POWER** to PMIC

2)  trigerring by ext_wakeup0

      ->this will turn on PMIC through the pmic-pwer_enable

     ->and finally, AM335x goes back to ACTIVE mode.

 

Thanks,

Devin 

  • 0
    TI__Guru**** 393215 points
    Hi Devin,
     
    RTC-only mode is described in section 8.1.4.3.5 of the AM335X TRM, Rev. J. Quoting from the TRM:
     
    Wakeup from RTC-only mode can only be achieved using the ext_wakeup0 signal. Once a wakeup is triggered using this signal, the device drives pmic_pwr_enable to initiate a power-up sequence by the PMIC. The device must go through a full cold boot upon wakeup from RTC-only mode.
     
    As you see this mode is entered/exited via the EXT_WAKEUP and PMIC_PWR_ENABLE pins. Sectiom 8.1.4.3.6 further says:
     
    If your application uses the RTC functionality and requires RTC-only mode, the internal LDO is required to enable proper wakeup signaling from the RTC domain. The proper wakeup signaling requires the following connections:
     
    • RTC_KALDO_ENn is grounded
    • CAP_VDD_RTC is connected to 1uF decoupling capacitor to ground
    • RTC_PWRONRSTn is connected to 1.8V RTC power on reset
    • PMIC_POWER_EN is connected to power input of PMIC
    • EXT_WAKEUP0 is connected to a wakeup source
     
    Lastly section 20.3.3.8 explains the functionality of the PMIC_PWR_ENABLE pin.