AD7172-4 Even Numbered Channels

Hi All

After finally getting the above device to behave sensibly, I have come across another issue. While it does not completely stop me using the chip, I would like to get to the bottom of the issue.

From what I am aware, this device allows any of the 9 physical input pins to be directed to any of the 8 internal measurement channels. These channels then can be directed to any one of 8 'setups'. Each setup then has associated, filter, gain and offset settings. 

I have setup all eight channels for internal chip testing, (i.e. Vdd and Vss as the reference and the 'test pair' which produces 1V as inputs), thereby not relying on any external input. 

I have all the 8 'setups' identically as have the filters. The gain and the offset have not been altered. 

Now when the channels are directed to setups 1, 3, 5, 7 - the measurement I get is around the 1 V mark. 

However when directed to setups 0, 2, 4, 6 - the measurement value is 0xFFFFFF.

Now given the setup, filter, gain and offset are configured identically, I am not sure why the device is behaving like this. 

While I only really require 2 setups in my application, it would be nice to get to the bottom of this problem.

Anyone have any ideas.

Thank you

Kind regards

Chithambaram 

  • 0
    •  Analog Employees 
    on Jan 19, 2017 5:50 PM over 4 years ago

    Hi, Chithambaram.

    I have tried to enable all of the 8 channels, each channel are directed to 8 different setup with the same configuration. I have selected AVDD1-AVSS as reference and the test pair as input voltage to all of the channels and all of them returns a value of 1V. Have you tried to read back the register contents for each setup to check if you have configured the part correctly? Possible reason why ADC returns a value close to full scale is you have an invalid reference, over range and under range input voltage. Can you read back all of the 8 setup configuration register as well as the channel registers?

    Thanks,

    Jellenie

  • Hi Jellenie

    Thank you for you reply.

    I have tried reading back the channel config and related setup registers and they are being returned as expected. 

    However, I am only configuring the setups that I am interested in. One idea I had was to configure all the setups, regardless of whether they were used or not. 

    I will try the above an let you know.

    However I am still troubled by the fact that when the channel is directed to odd numbered setups the device seems to behave. 

    Thank you

    Chithambaram

  • HI Jellenie

    I think I have figured it out. I found a bug in my set register method specific to setting the offset registers.

    These registers are 3 bytes long, however I was only sending 2 bytes. Therefore, when setting all 8 offsets in sequence, the command byte from the second instruction was probably being used as the 3rd byte for the first instruction. Therefore the chip was probably being setup in an unusual way. 

    I think what made this hard to trace was the fact that the device was seemingly working for the odd channels. 

    I have fixed the set method and tested with setups 0 and 2 and it seems to behave.

    Thank you

    Chithambaram

  • 0
    •  Analog Employees 
    on Jan 22, 2017 7:56 PM over 4 years ago

    Hi, Chithambaram.

    Good to hear that you have solved the issue. If you have any other question especially regarding your application, please let us know.

    Thanks,

    Jellenie

  • 0
    •  Analog Employees 
    on Aug 2, 2018 3:42 PM over 2 years ago
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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    EZ Admin