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PCA9554PWG4 concerns on POR errata

BrandonAzbell
Guru 64500 points
Other Parts Discussed in Thread: PCA9554, TCA9554

A customer has inquired about a recommended mitigation strategy for the POR errata on the PCA9554.  Initially, I indicated the use of the TCA9554 as an alternative, but there are some follow on questions.

Looking at the TCA datasheet, I don’t see mention of latch up but there are detailed diagrams regarding reset.

 

Does the TCA part eliminate latch up but doesn’t guarantee reset unless applied signaling follows the diagrams?

 

Thank you.

  • 0
    TI__Genius 16510 points
    Hello Brandon,

    Their use of the term "latch up" should be clarified. In the PCA part, when the POR circuit requirements are not met, the POR circuit does not send a reset signal to the digital core, which means the digital core can start up in any state. It may not respond. Latch up testing typically refers to a specific process-type of test, which is not what we are referring to.

    In the TCA parts, the POR circuitry was redesigned and has a much wider window of allowed ramp rates. The values supplied in the datasheet are the values that were tested. For that reason, we only guarantee that a RESET occurs if the power up is within these values. However, the times given in the TCA part allow for very fast power ups and even extremely slow power ups (2 seconds)
  • 0 in reply to Jonathan Valdez
    TI__Guru 64500 points
    Agreed. This really should have been "lock up". Does the TCA9554 design preclude lock up or just make it less likely?
  • 0 in reply to BrandonAzbell
    TI__Genius 16510 points
    Brandon, You are correct.

    The TCA POR circuit is significantly more robust across ramp rates and effectively precludes lock up. We have not seen any cases of a lock up.