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AM62L: Power VDDA_3P3_USB with the same rail as the PMIC

Marinus Holzner
Intellectual 1580 points
Part Number: AM62L

Tool/software:

Hi,

The PDN for the AM62L is mentioning that the VDDA_3P3_USB and VDDA_3P3_SDIO power rails should be powered via an external DCDC in paralell to the TPS6521401. But can this DCDC be removed if the PMIC is powered with 3.3V only? So that VDDA_3P3_USB, VDDA_3P3_SDIO (with the power switch) and the TPS6521401 are connected to the same 3.3V power rail or does this create issues on the power sequencing?

Thank you!

Marinus

  • 0
    TI__Mastermind 22491 points

    Hi Marinus,

    Thanks for reaching out. Connecting a 3.3V pre-regulator directly to SoC rails like "VDDA_3P3_USB" would technically work under normal conditions but it is not recommended. Here are some of the reasons:  

    • The external 3.3V discrete rail needs to be power cycle if a fault is detected on any of the SoC rails or when a COLD reset is triggered. This is handled by one of the PMIC GPIOs which is pre-configured to enable/disable the external 3.3V rail. 

    • If an OFF request is send by software (I2C) or by hardware (by pulling the PMIC enable pin low) the external 3.3V IOs will stay supplied creating an unknown state for the SoC power domain.  

    • Having the external rail (power switch or DCDC) also allows to pull the SoC PORz low as soon as a fault is detected on the 3.3V because customers can combine the PMIC and DCDC power-good signals as shown in the diagram below (highlighted in yellow). 

     

    Thanks,

    Brenda