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ADS8681: How the damping resistors in the Evaluation Board was selected

ASLAM SHAIK
Prodigy 30 points

Part Number: ADS8681

  1. The R25 resistor of 0.22ohm and R12 resistor of 0.47Ohms in the EVM schematic shown below. Is it required in the design to use these resistors. Please confirm. As the datasheet has not recommended any snubber design guidelines, I want to make sure whether TI recommends these 2 resistors if I am using internal reference. If I need to use the resistors, is there any design guidelines to determine the value of the resistors based on my design. Whether these resistor values depends on the sampling frequency?image.png
  • +1
    TI__Expert 7960 points

    Hello Aslam, 

    The resistors in series with the capacitors on both REFIO and REFCAP are not required. For the REFIO they are added by recommendation of the voltage reference used as well as a good practice to ensure there is a low ESR on those pins. 

    When using the internal reference this is the recommended: 

    For the REFCAP we do suggest using a capacitor with an ESR less than 0.2Ω. In the schematic shared, the 0.22Ω was included as a precaution, but if the capacitors used already meet that specification there is no need to add any additional impedance. So long as Figure7-7 is met and the layout recommendations are met as close as possible then that should be sufficient. 

    Best regards, 

    Yolanda