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Original question:

PCA9554: PCA9545 digital inputs damaged caused by too long high rise times?

PCA9554: PCA9545 digital inputs damaged caused by too long high rise times?

Alois Lang1
Prodigy 40 points
Part Number: PCA9554

Hello,

I made some measurements of one input of the PCA9554.
I measured at Pin 12 of the PCA9554 to GND.

I couldn't find any spikes, over - or undershot of the input signal at the Chip input point (PIN 12 of PCA9554).
Conntecting the external connector to the plug will generate some over - and undervoltage peak (+1V /-1V to the supply voltage) at the point of connection.
This voltage peak at the connector is filtered by the RC-LP-filter in front of the Chip input, so the PCA 9554 doesn't see any dangerous voltage.

BR Alois

  • 0
    TI__Guru 73201 points

    Hey Alois,

    How much resolution/sampling do you have on your scope when you saw the +1V/-1V during the connecting event?

    It may be possible that the voltages could be larger if the sampling on the o-scope is not high enough to capture all of the event in high resolution.

    -Bobby