Hi all!
I use one ADS1248 and have connected 2 Pt100x resistors (2-wire) on AIN0 / AIN1 and AIN2 / AIN3. The measuring current (IDAC) for the Pt100 is connected with IOUT1 resp. IOUT2. I use the following IDAC currents: 0.75mA, 1mA, 1.5mA - all now problem during normal operating conditions (I use the ADS1248 since about 1.5 years for my projects).
Now the problem: Under burst-test conditions (2kV burst voltage) we measure (reproducible) measuring-current (IDAC) values at the Pt100 resistors, that exceeds the specified tolerance limits! For example the following 3 measured values per nominal IDAC-value (the first value in each line is the setup nominal IDAC0 value, the other values are measured):
0mA: 0 0 0
0,75mA: 0,545mA 0,713mA 0,5627mA
1mA: 0,721mA 0,944mA 0,829mA
1,5mA: 1,087mA 1,423mA 1,251mA.
Each measuring-current value is constant for about 1 - 5 seconds, then change to another (wrong) value. After burst-test, the measuring-current keeps at a constant but wrong value! How is it possible, that the ADC produce such wrong IDAC values? The only way (we have found) that the ADC works correct after such burst-conditions, is to reset (or power-up) the ADC by RESET\ pin. Just recovering all ADC-registers with there nominal values don't work.
Do you have any idea what's wrong here?
My problem is, that we have already a big amount of units in the field. So we cannot just change the hardware circuit (better EMC protection), i need a firmware solution at this time!
Best regards,
Markus.