PCA8574D very temperature dependent

[troyzwork]

We are troubleshooting a circuit that uses the mentioned I/O expander.  We have a very infrequent intermittent failure.  In our troubleshooting we decided to us a low heat, heat gun.  In doing so we were able to notice erratic behavior of the 8 bits of this IC when a small amount of heat was applied.  The output was commanded to a static state.

We were very careful not to 'heat' the IC to a 'hot' condition, it was simply warmed, my guess was 35-40C as it never was hot to the touch, only warm.

Seeing this reaction with a suspected failing part and how it reacted with only 'warming' of the IC, I put this test to 3 other PCA8574D that are in similar circuits but fully functional.  To my surprise the other 3 ICs had a similar reaction!

I am really hoping to understand why such a small amount of heat creates havoc on the outputs of this device.

Thanks for any input!

[reyes]

Hi,

According to the datasheet, the operational ambient temperature range for the PCA8574D goes from -40C to +85C, so, operating at ambient +35C or+40C should not be a problem.

Please share more details of the error you are seen, including screenshots or signal plots if possible.

Also if you can measure the temperature on the IC package when doing the test, would be very appreciated.

Regards,

Jose