Hello everybody,
I work on a project where we're using a ADC, the AD7622 which is a 16bits, 2 MSPS converter.
We have a problem with it, it doesn't work.. we chose this way of working and interface :
- we work in parallel mode : ser/par = 0 to read the 16 bits directly
- Byteswap = 0 to have the LSB on D[0;7] and the MSB on D[8;15]
- WARP = /NORMAL = 1
- OB/2C = 1 to make the output coding straight binary
- PDREF = PDBUF = 0 to choose the internal reference whis is 2.048V
So we are in parallel interface and we chose to work with /CS = 0 and /RD = 0 to be in Master Parallel Interface then we only use /CNVST to initiate a conversion.
Moreover I thought that it was the signal CNVST that I didn't generate as well but that's false because we use differents ADCs like the AD7656 and it works! We need the AD7622 because of his accuracy.
When I make the signal's acquisition, I can see that the bits 5 , 6 , 7 , 8 , 9 are oscillating which is not normal because I convert an analog signal coming from pile (with V=1.3V < Vref). Normally it should be the LSBs bits which can oscillate but not the bits 6 7 8 9 ....
I respect the different timings to be sure to read when the data is durable. When I initiate a conversion with the CONVST bit I can see the Busy bit going High so the ADC works but the final result is disturbing...
Furthermore, every decoupling capacitor and differents resistance as shown at p.16 have been respected. DC ground to a DC ground and analog ground to an analog ground.
This is a differencial inputs ADC, the inputs must be symetric. That's ok because we put a ground (0V) onto the 2 inputs In+ and In- so it should work.
I don't understand why the ADC doesn't work, maybe I didn't understand a part of the Datasheet especially interface and modes..
If anybody can helps me it would be nice.
