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TLV320AIC3256: Unipolar Configuration and MICBIAS of 2.5V

Part Number: TLV320AIC3256

We are having difficulties in achieving unipolar configuration for headset connection and associated MICBIAS of 2.5V

Below are the configurations we have done to set the MICBIAS:

Intended operation

Register/s Updated

Bit/s Updated in the register

Bit/s Value

Power-down MICBIAS

Page 1 / Register 51: MICBIAS Configuration Register



Set MICBIAS to 2.5V

Page 1 / Register 10: Common Mode Control Register



Page 1 / Register 51: MICBIAS Configuration Register



Power-up MICBIAS

Page 1 / Register 51: MICBIAS Configuration Register




We have set the following:  DRVdd_HP = 3.3V, AVdd = 1.8V, VNEG = GND

With the above configuration, we observed MICBIAS of 3.3V instead of the anticipated 2.5V.Then we tried to set MICBIAS to other possible values but observed that it is always equal to the source(AVdd or DRVdd_HP) selected to generate the MICBIAS i.e., either 1.8V or 3.3V.

For further detail, I have also attached details of all the other configurations that we have done. 


TLV320AIC3256 CodecConfigurations.xlsx


  • To further clarify, we are looking for next steps in order to debug the problem of setting MICBIAS, specifically in the scenario above when MICBIAS is 3.3V instead of 2.5V in unipolar configuration. 


  • Hi Jack,

    We're looking into your query and will get back to you as soon as possible.  Will try to have some detail early next week.

  • Hi Jack,

    The register settings for MICBIAS register appear to be proper.

    When Page 1, Register 0x33 is set to 0x68 the MICBIAS voltage should be 2.5V for CM setting of 0.9V.

    To get 3.3V, the registers setting should be 0x78. But since you are getting 3.3V for a 0x68 setting, it could be a register programming error or some sort of a short on the board.

    Could you please remove R933 from the board and directly measure the voltage on Pin 23?

    If it is a programming error, please read back Page 1, Register 0x33 and verify that the register value is indeed 0x68.

    Best Regards.

  • Let us know if you need further assistance on the above. I shall close the thread. Responding will re-open the thread..

    Best Regards.