Similar posts have been made, but not with conclusive responses:
https://community.nxp.com/t5/Other-NXP-Products/PCA9745B-SDO-high-impedance-state/m-p/994889
https://community.nxp.com/t5/Other-NXP-Products/PCA9745B-SDO-stays-low/m-p/1325772
We are also observing the PCA9745B SDO pin continue to drive low (not high-impedance, as indicated by the datasheet) when the _CS input is high.
To test this, we isolated the PCA9745B's SDO output (not connected to any other SDO or Master, and connected the pin to a simple voltage divider (10k-ohm to 3.3V and 10k-ohm to GND). In this configuration, we would expect to see ~1.65V if SDO is truly high-impedance.
- After applying power the chip and with _CS HIGH and _RESET HIGH, the SDO pin measures at 0V.
- However, as was mentioned in one of the posts above, if we set _RESET LOW, the SDO pin does measure the expected 1.65V, while the PCA9745B is held in reset. But, as soon as we set _RESET HIGH, the SDO pin drives 0V again.
- Keep in mind, this is the behavior when powering the chip... there is before attempting any SPI communication, so I don't see how there could be a signal-timing issue. When we do attempt SPI communication, the Device properly recieves and processes the data like it should, but when the _CS returns HIGH after communication, the SDO line always drives 0V.
Is this a known issue with this part?
