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TIDA-00366: Discrepancy in Cutoff Frequency of differential filter

Sanghun Kim
Prodigy 20 points
Part Number: TIDA-00366
Other Parts Discussed in Thread: AMC1311

Dear TI Team,

In the "Design Guide: TIDA-00366" on page 19, the text states:

"The output of the AMC1311 is filtered using a differential filter (a combination of R75, R80, and C52) with a cutoff frequency of approximately 94 kHz."

However, based on the current values of R75, R80, and C52 provided in Figure 14, it appears impossible to achieve a 94 kHz cutoff frequency.

I would be grateful if you could verify this information and provide the correct component values to achieve the intended cutoff frequency.

Thank you for your time and assistance.

Sincerely,

Sanghun Kim

  • 0
    TI__Intellectual 1620 points

    Hi Sanghun,

    Thank you for evaluating this reference design and reaching out to us on this question.

    I agree with you that it may have been a mistake here, because for R75, R80 and C52:

      - the time constant is tau = 4.7kΩ * 2 * 0.01uF = 94uS, and thus the cut-off frequency is f = 1/(2*PI*tau) = 1.694kHz.

    Refer to the description in the bottom of page 15, for the filter by R12, R15 and C11:

      - the time constant is tau = 4.7kΩ * 2 * 180pF = 1.692uS, and thus the cut-off frequency is f = 1/(2*PI*tau) = 94.1kHz.

    We will correct it in next revision.

    Best regards,

    Jerome Shan