Forum Post: RE: ADS1248: violating PGA Common-Mode Voltage Requirements but still measure correctly

Christof, I'm sorry, but we don't have any more detail or data about the drive of the PGA going into the supply rails. Also, we don't have a convenient drop-in replacement device. As we've developed new devices, we've changed feature sets, pinouts and larger packages for smaller packages. Based on what you've shown, I think the ADS124S08 would be the best replacement device. However, it comes in a 32 pin TQFP or leadless QFN package. I'm not sure what the best solution for you will be. There are two possibilities that I can think of that might work, but I don't know enough about how your system is put together to be sure. The first possibility is to make a bipolar supply for the ADS1248 . It doesn't necessarily have to be ±2.5V for the AVDD/AVSS supplies. You could set AVSS to -0.2V and still have 100mV of room to the negative supply in gain of 1. A device like the LM7705 generates a voltage of -0.232V and I believe it has been used for this purpose. The second possibility would be to raise up PGND by a similar amount. This could be done by shunting the measured current through a Schottky diode, or a shunt reference. If you have more questions about putting together an alternate solution, please post back and we can work on it more. Joseph Wu