Hello!

I am currently working on a project where I use dual 16 bit AD converter AD7902 by Analog devices.

It seems that one of the 2 channels fails, while the other one works fine with same code and wiring. I have checked wiring and connections and everything is ok.

It fails in a manner that the bits sent out (and consequently data) aren't correct. 16bit data out stays the same as long the analog input voltage is the same - it is not like it would generate a random number (there is some noise on LSB of course). The problem is that data out is not proportional to applied voltage. I have not managed to determine how it is related to it.

What are your thoughts on that - is it possible that only 1 channel fails? Is it probably due to my inappropriate handling or a manufacturer's fail?

Thank you for your opinion.

 

Can you supply a diagram of the circuit?

 

Here you go from AD7902 pdf

 

My concern was how you have it connected. Do you have a diagram of your circuit?

 

At first I had it connected in daisy chain configuration and channel nr 2 was giving incorrect data, so I reconfigured it to the following 3 wire single mode and concluded that channel nr 2 fails, while ch nr 1 works fine. Additionaly I put everything apart , moved the whole circuit to a different location on breadboard, and reconnected. Ch 2 still fails. With Voltmeter I checked all pins directly on ADC (not through breadboard), and they all have correct voltages. I used pcb adapter for the chip so I can use it on a breadboard - all connections between chip pins and adapter pins have been checked.

Could it be that ch2 doesn't work correctly unless also ch1 is in use? ch1 was completely disconnected when I tested ch 2 and vice versa. Also it doesnt say in datasheet that channels affect each other in any way.

 

No, the operation of channel 1 doesn't affect channel 2 in the way you describe.

You have three possible points of failure:

1. The chip is defective or damaged.
2. There is something wrong in your circuit that connects to the device.
3. There is something wrong in your software.

Without a schematic and information on how you are controlling this device there is nothing more I can say.