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TS12A12511: Sequencing requirements

Narek
Prodigy 235 points
Part Number: TS12A12511
Other Parts Discussed in Thread: TS5A12301E

Hello.  I am considering using the TS12A12511, however, section 10 of the datasheet is giving me pause.  That section indicates a requirement for sequencing VCC followed by NC, NO, and COM.  In my application, VCC and NC will be tied together, so when VCC comes up, NC will come up at the same rate.  COM will come up at the same rate as well since IN will be low when VCC ramps up.  NO will be low and not come up for quite some time after.  Is the sequencing absolutely necessary or will the device function properly give my application description?  Thank you.

  • 0
    TI__Mastermind 45400 points

    Narek,

    The power sequencing comment is in the datasheet for all passive CMOS FET switches.  There are protection diodes on the signal path that can conduct to Vcc if the signal path sees a voltage before the supply.  When these diodes conduct they can pass large current and back power the supply rail or turn on the switch. 

    If you are concerned about back power or signal path isolation on power up you can use a switch with powered off protection like the TS5A12301E.   You can see more information in the technote in this post.

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    Prodigy 235 points
    Hi Adam,

    Thank you for the reply. I'm very limited on the amount of supply current. The one you recommended consumes about 10x more (max) than the device I am considering. After reading a bit more on CMOS latch-up, it seems to me that as long as any of the inputs are not asserted *before* the supply, there should not be any problems. In my applications the inputs are asserted simultaneously with the supply, so none of the ESD diodes should conduct. Do you agree?

    Thanks,
    Narek
  • 0 in reply to Narek
    TI__Mastermind 45400 points
    Narek,

    I agree, but TI recommends that Vcc is powered before any signals are on the signal path as you mentioned in the datasheet.

    Thank you,
    Adam