During normal operation the ADC's analog inputs are per the data sheet: the plus and minus inputs swing +/-0.45V, centered around VCM. i.e., assuming Vcm = 0.8V, the plus and minus inputs each swing between 0.35V and 1.25V. However at the start of every image we insert a marker pulse stream into the analog signal which forces the minus input to ground and the positive input swings between ground and 1.8V. The high and low levels are each 3 conversions long (40ns). We are using the part in 16ch, 12-Bit mode with 75MHz conversion rate.
These 1.8V marker pulses are within the Absolute Maximum Ratings but well outside normal operation. However the data sheet brags of recovering in 1 Conversion Clock (5MHz overload input, 6-dBFS overload) so I'm hoping the converter will give usable data on the marker pulses and recover reasonably quickly. We don't need high accuracy on these marker pulses.
Can you tell me how the part will react to these marker pulses. Assume the high and low levels are each 3 conversions wide 40ns).
Specifically, I would like to know:
1) Will this work at all, or will the converter not give useful data during the marker pulses.
2) What data code should I expect with both inputs grounded? I expect it will be 7FF +/- some errors due to exceeding the input common mode range.
3) What data code should I expect with INP = 1.8V and INM = 0.0V? FFF?
Thanks, Bob