...
With those fizes, we got communication happening over the external SPI port to theMUX. Still not getting any useable data from it though (all ~2.1V for the measured channels - they should be around 1.5V or below according to the the calculations above. Note that the measurements are just noise - they can easily be ‘adjusted’ by touching them or probing with a scope (the scope input impedance pulling the measurement down to almost 0V.
I really wish this board had better test points for all of the communication outputs - but that’s beside the point.
...
I noticed this seemingly weird behavior of the 3V0_VREF2 pin measured at the input to the buffer. The device turns on, takes 12 temperature measurements, then goes back to sleep. It seems the 3V0_VREF2 is going to sleep between every AUX measurement. The period between the dips in 3V0 lines up with what I'm seeing on the logic analyzer for the read AUX commands, roughly a 13mS period (note I had slowed down the SPI communication for this to get a better visual of the external SPI port on the scope earlier, and the 13mS period will not be what is in the car). Liam Hawkins Is this expected behavior? Should the references be powering off? Sleep transition takes 2s, and the Green LED for 5V0 indicating DRIVE is always on, so the IC seems to be going in to STANDBY state.
...
This is happening whether the thermistors are connected or not, so it should not be due to overloading the buffer or the regulator.
Next steps I’ll try getting some wires soldered to the TQFP mux package and hopefully connect them to the logic analyzer or scope so we can see what is actually happening (I had verified communication was present measuring just 1 channel at a time, so I am unsure if timings are accurate.