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AD7173-8: ADC not working with input buffers enabled

Category: Hardware
Product Number: AD7173-8

Whenever I enable either the analog input buffers or the reference input buffers for the ADC, we read a value of -8385495 (-27.5V) when 0V is applied differentially and -2294797 (-7.5V) when 10V is applied. This only happens on certain ADCs (we have 4 on our board), and it is a different ADC on each board so I don't think it's a schematic/layout issue. Our power supply is slightly noisy, could this cause any issues? We measured a peak to peak ripple between each supply and ground of 260 mV on the +2.5V supply, 260 mV on the +3.3V supply, and 332 mV on the -2.5V supply.

I also read back the value of the setup configuration register to make sure the buffer enable [1:0] bits were being set correctly for both the reference buffers and the analog input buffers.



Added product number on subject
[edited by: JCCillion at 12:17 AM (GMT -5) on 14 Feb 2024]

Top Replies

    •  Analog Employees 
    •  Super User 
    Feb 14, 2024 in reply to Psud +1 verified

    Hi  ,

    First of all, the allowable input range of the AD7173-8 is only +/-Vref and the absolute AIN voltage limits when buffers enabled is from AVSS to AVDD1-1.1. I would not recommend operating the…

  • Follow-up - it seems like resetting the ADCs after power-up fixed the issue, as mentioned in the datasheet. We had a situation where out of the 4 ADCs on our board, reading the first ADC would never work, but reading any other ADC would, regardless of which ADC was first. Any ideas on why a reset after the power supplies were stable fixed that?

  • Hi  ,

    First of all, the allowable input range of the AD7173-8 is only +/-Vref and the absolute AIN voltage limits when buffers enabled is from AVSS to AVDD1-1.1. I would not recommend operating the device outside the specified value. This may cause accurate readings and worst damage the part if the absolute maximum rating is violated.



    In my calculation, your measured value of 8385495 when 0V is applied seems correct to me when converted to voltage. Converting the code to voltage in bipolar mode will result to -0.000927746V when using a 2.5V reference. You may refer on this FAQ on how to convert data output code to voltage.

    After a power-up cycle and when the power supplies are stable, a device reset is required. Resetting the device will reset the on-chip registers to their default values. Any glitches during power-up can cause corruption of the registers. An over-voltage may also cause the on chip registers to be corrupted.

    Hope this helps.

    Regards,

    JC

  • Hi,

    Sorry, I forgot to mention that the input goes through a filtering stage which attenuates the signal by about 10x before going into the ADC.

    Thank you for the response!

  • Hi  ,

    Glad to assist you. I hope the FAQ also helped in verifying your measurement.

    Regards,

    JC