At work we have implemented an Analog to Digital Converter on our own PCB using the AD7687. We currently have 10 of these boards in constant operation. We have had 2 of these boards fail in a way that looks like the ADC IC is no longer running. All other boards have been running fine.
All power rails look great on the ADC. Vdd is 5V. Vio is 3.3V. data_in is driven to 3.3V to allow for operation in 3 wire serial mode. clock and convert are both driven directly off of a Spartan 6 FPGA and there edges look great.
When a test sine wave is input into the PCB and the output is plotted the output flips between a count of 0x0000 and 0xFFFF at the same frequency as the input signal.
Could you advise on any reasons this would occur?