AD7609 Input noise

Hi...

I would like to develop a tool for voltage acquisition using the AD7609. So I bought your EVM board (AD7609EDZ). And reads the data using the SPI interface. Differential input reads several batteries. However, when I read only one channel, it reads very well. If I read several channels, the data moves about + 40mV.
How can I solve this problem? I think the AD7609 is a really optimal solution for the system I want to develop.
Please help me.
Best Regards,
  • 0
    •  Analog Employees 
    on Jul 18, 2018 7:26 PM

    Hi anizard,

       Please send scope shots of your gathered signal. Was the offset showing when shorting the inputs to ground? You can also check the ground connection of the source to the AD7609 eval board and make sure that it connected with a short wire and the same length for V+ and V- as possible.

    Regards,

    Jonathan

  • Dear Jonathan

    Thanks for your reply.

    I tested AD7609 eval board too.

    I attached the file( signal waveform and test environment).

    In the waveforms, the first is for channels 1 and 3, the input for 1.0V, and the channel 2 is open. This will swing +40 ~ 50mV of channel 3 voltage.
    However, if you input 1.0V for all channels 1, 2, and 3, the voltage is read very steadily.
    The cause is unknown.
    The equipment I develop must use the channels randomly, so I need to read the data reliably even without interim use.
    Please help me.

     

    Best Regards,

    Bum-Jin, Kim

  • 0
    •  Analog Employees 
    on Jul 19, 2018 6:22 PM

    Hi Kim,

    AD7609 allows simultaneous sampling of all analog input channels.All channels are always converted The results for any unused channels are still included in the data read. It's recommended to connect all unused analog input to AGND.

    Best Regards,

    LLoben

  • Hi LLoben

    I have tried various tests on the AD7609.

    Currently I am testing with differential mode. The way you told me, I connected the unused channels to AGND, but the symptoms were the same. So I have shorted V + and V- channels that I do not use. Then the voltage fluctuation symptoms were improved.

    I have some questions about the AD7609.
    1. Deviation by channel
         - ex. CH1 read as 1.0V. When the same battery is put in CH2, it is read as 0.960V.
                 There is a variation in the voltage value per channel.
    2. I am currently using the AD7609 with a + -5V input range.
          When all channels (8 channels) are connected, eight 1.6V batteries are connected
         and the total voltage is 12.8V. 
         When the battery voltage sum value exceeded 10V, the voltage of each channel
        shook about 20mV.
         Could this happen?
    Best Regards,
     Bum-Jin, Kim
  • 0
    •  Analog Employees 
    on Aug 24, 2018 12:52 PM
    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.

    Thank you,
    EZ Admin