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Input Impedance of HMIC audio input pins for TWL6040

J Evans
Prodigy 200 points
Other Parts Discussed in Thread: TWL6040

Hi!

Does anyone have any information about where or how to find the input impedance of the HMIC pins for the TWL6040 in the datasheet?

I will be using a MEMS analog microphone (ADMP401: http://www.analog.com/static/imported-files/data_sheets/ADMP401.pdf) to provide the analog signal to the TWL6040, but in order to find the capacitance value for the capacitor placed between the devices on the analog signal circuit, the input impedance of the TWL640 HMIC needs to be known.

Of course, there is a minimum capacitance value that can be used, but I'd like to match the capacitance to the impedance...

Thanks for your help in advance!

James

  • 0
    TI__Guru**** 189401 points

    Hi, James,

    We don't support the TWL parts here in the audio forums... 

    Let me move your post to the forum where the apps engineers for those devices monitor.

    -d2

  • 0
    TI__Intellectual 1915 points

    Sorry for very late reply

    Ssingle ended input resistance is available in TWL6040 datasheet:

    Single-ended input resistance min:160 typ:200 max:240 unit:kΩ

    Hope this helps. Alain.

  • 0 in reply to AlainC
    Prodigy 200 points

    Hi Alain,

    Thanks for your reply!

    I had found the input resistance in the TWL6040 already (thank you for confirming it though), but I was curious where I could find a capacitance/inductance value for the HMIC interface to calculate the input impedance.

    I doubt that each I/O pin has the same input impedance value, but maybe I'm missing seeing those values in the TWL6040 datasheet?

    Thanks again for your help...

    James

  • 0 in reply to J Evans
    TI__Intellectual 1915 points

    James, I've looked in other documents I have but I couldn't find it. Only input resistance is documented. I would guess that input capacitance would be in pF range and input inductance in nH (mainly due to bond wires) so overall PCB traces would play a more important role than device itself.

    Best regards, Alain.

  • 0 in reply to AlainC
    Prodigy 200 points

    Excellent. That answers my question and you have been most helpful. Thanks for replying even though this thread is somewhat dated. I appreciate it.

    James