topic Re: PCA9518 in Other NXP Products

PCA9518

AbdallaDawoud — Sun, 05 Nov 2023 12:53:41 GMT

I am facing a weird issue, I am connecting ATMEGA128 (running on 5v VCC) to PCA9518 through TSX0102 for both SCL & SDA lines. the PCA9518 is included to buffer I2C communication between ATMEGA128 and four other boards. The SCL0 & SDA0 are 3.3v, while all other ports are 5v (pull-up resistors connected to 5v). SCL signal can be seen on all ports, but with lower frequency than targeted (66.2KHz instead of 100KHz) and SDA is always zero logic on all port no matter which one is enabled.

I am suspecting the cause to be one of the following:

1. Using PCA9518 in series with TSX0102 rise time accelerator which might be incompatible.

2. Using large bypass capacitors connected to VCC (3.3V) one 10 uF tantalum in parallel with 0.1 uF MLCC.

3. Connecting EXPSCL1&2 EXPSDA1&2 pull-up resistors to 5V.

4. Connecting all EN to 5v logic signals.

5. Not connecting extra pull-ups at the TSX0102 outputs.

attached is part of the schematic regarding this point.

Please can anyone assist in diagnosing the cause of the issue.

Re: PCA9518

MarkChapman — Sun, 05 Nov 2023 19:00:31 GMT

It's possible that the 3.3V SCL signal affects PCA9518. Try using a level shifter for 5V compatibility. Check connections thoroughly.

Re: PCA9518

guoweisun — Mon, 06 Nov 2023 07:05:07 GMT

Please share with your schematic here.

Re: PCA9518

AbdallaDawoud — Mon, 06 Nov 2023 13:36:54 GMT

Thanks Mark l, you were right. After careful connections checking again for the third time, it turned out that one of EXPSDA’s pull-up resistor was not properly soldered, having it well-soldered has resolved the issue completely.