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POR and RESETFULL order in power-down sequence

Nori Shinozaki
Intellectual 2430 points
Other Parts Discussed in Thread: UCD9090, TPS3808

Hello,

The data sheet(SPRS814A) says in "7.2.2 Power-Down Sequence" that,

"If a catastrophic power supply failure occurs on any voltage rail, POR should transition to low to prevent over-current conditions"

Does this mean that POR should be activate prior to RESETFULL and anythings in any power-down cases?

Regards,

Nori Shinozaki

  • 0
    TI__Intellectual 2430 points

    Sorry! the device is C6657.

    Regards,

    Nori Shinozaki

  • 0 in reply to Nori Shinozaki
    TI__Mastermind 46460 points

    Nori,

    Ideally, the power-down sequence needs to be the reverse of the power-up sequence.  This is stated in the same section of the Data Manual.  This includes the reset and clock inputs as well.  Controlled power-up and controlled power-down are needed in some applications such as boards used in hot-swap implementations.

    The note quoted above is slightly different.  This is meant to address the uncontrolled case such as a blown fuse.  PORz needs to be driven by 'power good' logic.  To prevent device damage during a power supply failure, the PORz input must be driven low immediately.  PORz low causes all outputs to be tri-stated which prevents over-current conditions due to contention.  Of course, the other power supplies need to be shut down quickly as well.  The C6657 cannot remain in a partially powered condition without impacting its reliability.

    Power monitoring and control logic is needed to enforce these requirements.  TI makes multiple families of devices including parts like the TPS3808 and UCD9090 for this purpose.

    Tom

     

  • 0 in reply to Tom Johnson 16214
    TI__Intellectual 2430 points

    Hello Tom,

    Thank you for advice.

    We couldn't sell TPS3808 or UCD9090 because customer's design schedule.

    They will use PLD to control the sequence.

    Regards,

    N.Shinozaki