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Original question:

TLV320AIC3120: Application questions

TLV320AIC3120: MIC input impedance

Kazuki Itoh
Genius 11060 points
Part Number: TLV320AIC3120


Hello team,

My customer is trying to calculate high pass filter cut off frequency composed of the MIC input impedance and external capacitor at MIC1LP.

  1. Could you please let me know the input impedance of MIC1LP?
  2. RIN value can be configured by page1 R48. Does it affect the input impedance?
  3. AGC will be used in the design. R48 value affect the input impedance if AGC is used?

Best regards,

Itoh

  

  • +1
    TI__Mastermind 22950 points

    Hello Itoh-san,

    Please find my answers below:

    1. The input impedance is determined by programming registers 48 and 49 on page 1.

    2. This is confirmed on the answer above. Configuring these two registers set the input impedance for the respective MIC inputs. 

    3. Registers 48 and 49 set a fixed input impedance and this affects the applicable PGA gain. Changing the PGA gain will not affect the input impedance. Additionally, the AGC works by changing the PGA gain and therefore, it will not affect the input impedance. 

    Regards,

    Aaron Estrada

  • 0 in reply to Aaron Estrada
    TI__Genius 11060 points

    Hello Aaron-san,

    In the datasheet, is RIN (feed-forward resistance) similar to input impedance?

    I know P1/R48 affects MICLP input impedance, but I don't understand how P1/R49 affects the input impedance.

    Could you please elaborate on that?

    If the AGC controls PGA gain, the input impedance at MICLP pin will be fixed value which is programmed by P1/R49, correct?

    Regards,

    Itoh

  • +1 in reply to Kazuki Itoh
    TI__Mastermind 22950 points

    Hi Itoh-san,

    That is correct. P1/R48 refers to the plus input and P1/R48 refers to the minus input. See the diagram below:

    Your question regarding the AGC is correct. The PGA gain will change but the PGA gain is determined by the input resistance selected. 

    Regards,

    Aaron Estrada