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ADS7952: ADC sense 100R series resistance failure

Goutam Maji
Prodigy 190 points
Part Number: ADS7952

Hi Team,

We are experiencing a ADC sense 100R resistor failure to open some times. To understand more in details please find the attached circuit below. 24V supply is getting reduced and get filtered with RC ( 100R and 470pF) and given to the external ADC.

Q1: we have seen sometimes the series resistance 100R is failing. Please let us know whether we need to change the resistor to higher value. or do you see any other reason of failure.

Q2: 470pF capacitor can I increased to 100nF to 470nF for better filtering the signal; this is for other noisey signal I need to use bigger capacitor

Q3: Output of the ADS7952 is going to the FPGA (10M25SAE144C8G) for ADC sensing. we have seen one time Three line going to the FPGA Pin has failed short. (refer 3rd circuit for details). I mean SDI and SDO and CLK line. Please suggest whether any circuit modification is needed to avoid the failure.

Let me know if you need any more information.

  • 0
    TI__Mastermind 24940 points

    Hello,

    What is your sampling rate? This device is a muxed input with a shared input driving op amp. One benefit of having this common driving input op amp is that each input does not need to be filtred individually. Is there a particulat reason why the RC filter is in series with the voltage divider? You can remove that RC filter and connect the 24V sense directly to the ADC.

    Increasing the filter capacitor on the RC filter on the sense line will increase the settling time for the input. I would suggest using the common op amp to do the filtering.

    Looking at the op amp circuit, it seems that the RC filter at the output is not optimized for the ADC. Using the Analog Calculator tool, inserting the specifics for the ADS7952, it seems that the capacitor is too large, and the op amp might not be able to fully drive the signal within the ADCs acquisition time. Also, the bandwidth of the op amp might not be good enough. I would suggest simulating the op amp and ADC to make sure the input is settling. the Precision labs Video: Building the SAD ADC Model will help guide you through creating a first order model for the ADS7952.

    I am not sure if i understand question 3, would you please clarify?

    Regards

    Cynthia