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ADS7854: Rref Resistors

Part Number: ADS7854

Hi Experts,

could you clarify the following: In 11.1 the layout recommendation shows small Rref resistors between REFIO pin and Cref.

Would you recommend those resistors regardless of whether the customer is using the internal or an external reference?

In the Reference Configurations in 8.3.1 those resistors are not mentioned.

  • Hello Simon,

    Thank you for your post.

    This small resistance can help with reference voltage settling and stability, especially for amplifiers which cannot drive a capacitive load directly. Some external reference ICs which have an integrated reference buffer will specify a range of ESR values to consider when selecting the output capacitor. Adding a small resistor in series with the output capacitor ensures this ESR requirement is always met. 

    At a minimum, I would recommend placing a 0-ohm resistor footprint before the 10 uF output cap. Our ADS8354EVM schematic shows a 220 mOhm resistor here, but the ADS8353-Q1EVM (same product family), was released more recently and uses 0 ohms as the default. 

    Best regards,

  • Hi Ryan,

    thanks for the elaborate answer. 

    speaking about the internal reference of the ADS7854: There is no ESR requirement mentioned in the datasheet, which means that in the case the customer uses the internal reference the resistor would not be needed, right?

  • Hi Simon,

    That is correct. 

    Regards,