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TS3A227E: Headset impedance and bias

Ortal Koren
Prodigy 80 points
Part Number: TS3A227E

Hello,

We are using TS3A227E. In the datasheet is attached to following diagram:

It seems that according to this diagram, the maximum resistance bteween Mic and Gnd could be 4KOhm, does this mean TS3A227E does not support headsets with higher resistance between Mic and Gnd?

Also, we are using a codec CS42L51 which receives 2.5V VDD, and can output a maximum of 0.8*VDD=2V. In the datasheet, the range that the device expects starts from 2.1V. Is it possible to operate the device with 2V as the bias voltage? 

Thank you;

Ortal.

  • 0
    TI__Mastermind 45575 points

    Ortal, 

    The TS3A227E device might have issues with high impedance headphones depending on what you are trying to do with the device.  The device has an internal ADC that has a finite range of impedance values it can detect.  There will be a point where the ADC maxes out its bits and all impedance will look the same to the device after a certain point.  Please see this post for more information. 

    The recommended operating conditions state that you can have a voltage between 0 and VDD. 

    Thank you,

    Adam

  • 0
    TI__Mastermind 45575 points

    Ortal, 

    The TS3A227E device might have issues with high impedance headphones depending on what you are trying to do with the device.  The device has an internal ADC that has a finite range of impedance values it can detect.  There will be a point where the ADC maxes out its bits and all impedance will look the same to the device after a certain point.  Please see this post for more information. 

    The recommended operating conditions state that you can have a voltage between 0 and VDD. 

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    Prodigy 80 points

    Thanks for your response.

    Regarding the MICBIAS voltage, I understand that applying 2V won't harm the device, but will the key press detection work? Since I can only set the expected MICBIAS voltage to 2.1 or more.

    Thank you

    Ortal.

  • 0 in reply to Ortal Koren
    TI__Mastermind 45575 points

    Ortal,

    Detailed information on the key press detection can be found on beginning on page 41 of the datasheet.  This will show you the formula you can use to calculate the voltage on sleeve/ring2 and the equivalent resistance detected by the device.  You can see that the mic bias voltage value can be different voltages but it is important that what ever voltage it is in constant.  The important part of the equation is the change in mic bias voltage when the key is pressed introducing a parallel resistor. 

    You can also adjust the resistance bins that the TS3A227E can detect to further tune your system.

     

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    Prodigy 80 points

    Thank you Adam,

    I am specifically concerned that if I use a 2V voltage, it would be a problem in terms of key press threshold voltage, otherwise why would I need to choose the MICBIAS setting as in the attached table from the datasheet?

    Thank you

    Ortal

  • 0 in reply to Ortal Koren
    TI__Mastermind 45575 points

    Ortal,

    The description states set this setting closest to the intended micbias voltage.  If you intend micbias to be 2V then 0x0h would be your closest setting.  This sets the micbias voltage in the equation above and then the device measures the voltage during the key press to calculate the delta mic bias voltage.

    Thank you,

    Adam