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PCA9555: PCA9555 lock up condition would create unknown output state at any pin?

Part Number: PCA9555
Other Parts Discussed in Thread: TCA9555

Hello Team,

I have a customer who has questions about the PCA9555 wrt lock up behavior.  

 " General question regarding PCA9555 device. : Can a POR caused latchup cause one of the IO pins to be an output and set it as a logic "high" state ?  We are having an issue with our box resetting and I am just looking at the whole function in our box that could be causing it with a power glitch.

We use an output from this device as an input to a reset control function circuit.  If we could get a false reading from the PCA device due to improper POR issue that would be great to understand. "

Please let me know of any suggestions/ comments with regards to this.

Thank you for your time.






  • Hello Kishen,
    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. It is possible if you have either a fast glitch on the supply you could get into the state. I would suggest having good decoupling caps close to the part. I would also suggest that you use the TCA9555 version of the part.

    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)

    I hope this helps.
    -Francis Houde
  • Thank you Francis. I understood the concept better. I will relay this information to the customer.

    I appreciate your help.