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Original question:

UCD9081: UCD9081 Power on and Power off Sequencers

UCD9081: Power on and power off sequence

Maurice Chiu
Prodigy 50 points
Part Number: UCD9081

Hi Ti,

I would like to use UCD9081 to control power on/off sequecen on our system

The system power rail is 3.3V and it will supply to other PMICs for other rails on system.

(1) power on: 1.8 -> 1.2 -> 1.05 -> 0.9 -> 0.55 -> 0.75 -> 0.5

(2) power off: reverse order

is it OK?

Besides, how to ensure correct power off sequence with uncontrolled power-off on system (3.3V)?

I worried the other PMICs will be turn off before UCD9081 achieve the off sequence.

Could I use MON pin to monitor system power rail 3.3V?

Thanks.

  • 0
    TI__Guru 60280 points

    Hi

    Yes, you can use UCD9081 to achieve the power up and power down order. Please configure the proper dependencies and off delay.

    if the 3V3 is used to power on the UCD9081, you need to give UCD enough time to detect the UV fault of UCD and finish the off sequence.

    If maybe better to monitor the VIN of the system 3V3 to give more times for the off sequencer . 

    Bottom line, you need test in your system to see time requirement

    Regards

    Yihe

  • 0 in reply to yihe
    Prodigy 50 points

    Hi,

    Followed by your advice, I use MON8 to monitor system 3V3 like below:

    (1) power on: 1.8 -> 1.2 -> 1.05 -> 0.9 -> 0.55 -> 0.75 -> 0.5 -> ASIC_RESET

    (2) power off: ASIC_RESET -> 0.5 -> 0.75 -> 0.55 -> 0.9 -> 1.05 -> 1.2 -> 1.8 (reverse order)

    When SYS_3V3 power off, MON8 will raise power off sequence (reset ASIC and disable PMIC)

    Can I use MON8 and EN8 for this purpose?

    Thanks.

  • 0 in reply to Maurice Chiu
    TI__Guru 60280 points

    Hi

    Yes, you can but, i would suggest to add a Schottky  diode between the VCC and Cap to avoid back feed. Also, since the diode has a forward bias, the VCC may be good to higher than 3.3V.

    Regards

    Yihe