Hi all!
We are trying to use the LM9822CCWM Analog Front End to digitize the output from a linear colour CCD but with poor result. Initially the device did not output any digital data att all (all zeros). After limiting the analog input voltage, (the reset puses from the CCD exceeded the 5.3 V max input voltage), things looked a bit better, but still all data bits after some time begin to exhibit transitions on both edges of the clock and none resemble the expected data, going gradually after several minutes running to no data output at all (all zeros). It is not a thermal phenomena since a very breif power-off/ power-on restarts the behaviour from scratch.
My best clue after we got the analog voltage in hand was the we had a clock reflection on MCLK causing false clocking on the wrong edge, but that was not the case. Careful termination of MCLK had no effect.
The next clue is that the device is extreamly sensitive to over- and undershots (deduced from the fact that behaviour changed when analog input was limited). I do not have any simple way to verify this, short of adding a buffer stage close to the device. We drive the clock signals from a small FPGA (XC3S50AN) and the traces to the device are quite long (approx 10 inches) due to mechanical limitations in the application. I have limited the drive to minimum (2mA slow LVTTL drivers, have also tested CMOS) and we are running at a fairly low clock speed of 4MHz MCLK in 6 bytes per pixel colour mode, which is the default setting, but there is moderate over- and undershoot on all signals.
Va is 5V and Vd is 3.3V. Both are regulated by LDO's in series from the same 12V source so they ought to ramp up in sync (verified on scope).
Anyone out there with a clue as to what is going on? Did we break the device when we had too large analog input or are there any quirks with this device that we are missing in the data sheet? We have exactly the same behaviour on the two different individualls we have tested so far.
Regards, /Lars
P.S. Remove the obvious from my email address in case you want to email me directly. D.S.