Our job is to debug and characterize custom image sensors. To do this we developed our own test systems that contain ADC's from Analog Devices.
One system has four AD9637’s, the other has eight AD9257’s. In both systems, the ADC’s have near identical connections. The only difference is that the AD9637’s have both their PWDN and SYNC pins floating.
According to figure 39 in the datasheet, these pins have an internal pull-down resistor. We assume this means that if PWDN is left floating, the device is always turned on.
What we observe is that the system with PWDN pins controlled by an FPGA operates flawlessly, but the system with the floating pins experiences random power-downs of the ADC’s. Sometimes this happens during startup, sometimes after a few seconds of operation, sometimes after minutes. Our question is: can this behavior be explained by the floating PWND pin, despite the internal pull-down?
I e-mailed this question to firstname.lastname@example.org, I got a reply requesting me to post the question here.