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ADS7253: Small 0.1-Ω to 0.2-Ω resistors for REF-x

Hirotaka Matsumoto
Guru 27585 points
Part Number: ADS7253
Other Parts Discussed in Thread: ADS7254, OPA350

Hi all

Would you mind if we ask ADS7253?

<Question>
There is the description as follows;
The REFIO-A and REFIO-B reference inputs and outputs are bypassed with 10-μF, X7R-grade, 0805-size, 16-V rated ceramic capacitors (C REF-x ).
Place the reference bypass capacitors as close as possible to the reference REFIO-x pins and connect the bypass capacitors using short, low-inductance connections.
Avoid placing vias between the REFIO-x pins and the bypass capacitors.
Small 0.1-Ω to 0.2-Ω resistors (R REF-x ) are used in series with the reference bypass capacitors to improve stability.

Does it require these resistance in case of reference output also?
In case of internal reference, it doesn't require or not?

Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Guru 54426 points

    Hi Hirotaka-san,

    When using the internal reference, the ADS7253 does not require the small compensation series resistor, and only requires a 10-μF X7R capacitor at each REFIO_x pin.  Attached below is a TI precision design showcasing the ADS7254 (fully-diff version of the device), where the internal reference drives a 10-uF bypass capacitor without the compensation resistor.  Figure 84 of the datasheet shows the Reference configurations and connections.

    http://www.ti.com/lit/ug/slau517/slau517.pdf

    The layout  recommendation is based on the ADSxx53 evaluation board, where the device can be set up with either an ext REF driver circuit or the internal reference.  On the eval board, the ext reference circuit uses the OPA350 as a buffer. The 200-mΩ resistor improves phase margin and stability of the OPA350 while driving the 10-μF bypass capacitor and REF input dynamic load. Stability analysis of the reference driver circuit is performed to select the optimal compensation resistor.

    Thank you and Best Regards,

    Luis

  • 0 in reply to Luis Chioye
    Guru 27585 points

    Luis san

    Thank you so much for your reply!

    Kind regards,

    Hirotaka Matsumoto