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TPS7A87: Time and input voltage required to reliably disable TPS7A87 and TPS7A90

Ken Hashi
Intellectual 790 points
Part Number: TPS7A87
Other Parts Discussed in Thread: TPS7A90, , TPS75005

Hello!

When disabling the TPS7A87 and TPS7A90 with the EN pin, how long must the voltage drop below VIL?
For example, tens of nanoseconds or a few microseconds?

My customer had heard of this before because he had trouble with the LDO (TPS75005) Power on reset problem, and he's worried that a newly hired LDO will have a similar problem.

Also, do the TPS7A87 and TPS7A90 have a POR (Power on reset) function?
According to the block diagram, these ICs do not include POR.


Regards.

k-hashi.

  • 0
    TI__Mastermind 29260 points

    Hello Ken,

    I am reviewing your question and will respond within 2 business days.

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    Intellectual 790 points

    Hello Stephen,

    Thanks for the reply
    Me and my customers look forward to your answers.

    Regards.

    ken hashi

  • 0 in reply to Ken Hashi
    TI__Mastermind 29260 points

    Hi Ken,

    My apologies for the delay, I've had to unexpectedly be out of the office today.
    Please allow 1-2 more days for a response.

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    Intellectual 790 points

    Hello Stephen,

    Thank you for your reply.
    I understand your situation.
    However, customers are waiting, so please be sure to answer.

    Regards

    ken hashi

  • 0 in reply to Ken Hashi
    TI__Mastermind 29260 points

    Hi Ken,

    The TPS75005 is a device tailor made for the C2000 series of microcontrollers, as you are aware.
    The TPS7A87 and TPS7A90 are not tailor made for the C2000 microcontrollers, but are more general LDO's in nature.

    The TPS7A87 and TPS7A90 have UVLO circuitry to consider in lieu of a POR circuit.
    The enable circuitry is not a precision enable. 
    The propagation delay will be the main consideration in how long you must hold the EN pin below 0.4V before seeing an effect on the output.
    The best data point we have is in the datasheet for the startup plots. 

    Figures 20-23 in the TPS7A87 datasheet, or figures 32-36 in the TPS7A90 datasheet, show the startup, with conditions, with an associated delay between the EN toggling and the output voltage changing.  I would use these as guides for the propagation delay during turn off.

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    Intellectual 790 points

    Hello Stephen

    Thank you for your answer.
    For the propagation delay of EN, refer to the delay time until the rise of VOUT.
    I understand that the delay time until the rise of VOUT varies depending on the load.

    Thank you very much.
    Best regards.


    ken hashi