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Original question:

PCF8575 : RESET problem

PCF8575: I/O sometimes powers up into a low-output state instead of a high as a default

Jeff Mercure
Prodigy 90 points
Part Number: PCF8575

I/O on this device sometimes powers up into a low-output state. I have 10K pullups on all of the Pxx pins. Not all devices show the problem. Currently 2 out of 11 units show the issue.

On one of the units ports P10 and P12 fail low on power up maybe 2% of the time. The other unit usually has only P10 fail. The same 10K pullup (driving a high-impedance input) is used on all GPO pins.

Software cannot be a workaround for this design since critical I/O is being set by the '1' default output.

The device is properly bypassed and +3.3V VCC rail is clean.

  • 0
    TI__Guru 62910 points
    Hi Jeff,

    It sounds like the internal registers are not being properly initialized, which suggests that there was an issue with the power-on-reset function. This can occur as a result of certain VCC ramp profiles. Can you please confirm that your VCC ramp behavior is within the guidelines listed in Section 10.1 of the device's datasheet?

    Regards,
    Max