Hi, We use an ADS8405i in the design and for some boards we can't get fullscale input for the ADC. It saturates near 1V instead of 4V. I have verified the Vref that is exactly 4.096V and the 5V is OK. I just see a small ripple of 150 mV on the 3.3V for digital power supply. I believed it was the ADC that was faulty but we have changed it and it's the same problem.Could you tell me what could reduce the scale of saturation of ADC with a clean AC+dc signal below 3.5V ? This ADC is replacing the ADS8401. The signal is fed by a buffer 0-5V AD8031 with 1KOhms at the input of the buffer (non inverter) and 15 Ohms to feed the ADC.