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How to implement a universal headset connector driver?

Jonathan9420
Expert 2056 points
Other Parts Discussed in Thread: TPA6166A2, TS3A227E, TS3A225E, TS3A226AE

TI makes several chips to go inside of a smartphone or similar device to automatically detect which type of headset is plugged in and route the mic signal appropriately.  tpa6166a2 ts3a227e ts3a225e etc.

Now how do you do the opposite without colliding with those universal chips?

If the phone is hardwired for OMTP or CTIA/AHJ, it should be possible to detect the mic bias voltage and switch our signal to that pin and ground the other one through a transistor.  But if the phone has one of your universal chips, how do we detect which type it is?  Will the two auto-detects conflict with each other?

This circuit from NXP shows an automatic phone detector, for instance:

But would this type of circuit conflict with a phone that has one of your universal detection chips inside?  How to make it work with all 3 types?

  • 0
    TI__Mastermind 45340 points

    Johnathan,

    I would point you to this other post to help you determine how this NXP device will react to an audio jack detection switch but that already seemed to find it :-)

    Most phones that contain one of these audio jacks will usually initialize the audio jack detection IC like the TS3A226AE as soon as you insert a device into the jack.  It will be tough to predict how the audio jack devices will detect the NXP design.  Could you measure the resistance on the NXP Earphone jack from the tip to Ring 2 and the Tip to Sleeve?

    1) If those two resistances are not equal the TI audio jacks will configure themselves to support the two different 4 pole configurations.  If this is the case the mic bias from the cell phone will be supplied to either sleeve or ring2.  Once this happens it looks like the NXP device can then use its comparator to detect where the mic bias is coming from and configure itself accordingly.

    2) If those two resistances are equal in the NXP design the TI audio jacks will configure them selves to support a 3 pole device grounding both Ring2 and Sleeve.  If this is the case I think it will be a more difficult problem to solve and do not have a solution at this time.

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    Expert 2056 points
    I'm not actually using that NXP design, just pointing it out as an example of something similar.

    We could do whatever we need to make it work, but ideally it would work with all 3 types of phone jacks: OMTP, CTIA, and Universal auto-detecting.
  • 0 in reply to Jonathan9420
    TI__Mastermind 45340 points
    Jonathan,

    Ok that makes sense. Hopefully you find enough information on these forums and datasheets to help you understand how TI audio jacks implement the universal auto-detecting. There are other universal auto-detecting ICs on the market than the TI family like the Fairchild FSA8049 that implement the detection a little bit different so you may want to look at other semiconductor manufactures' audio jack switches as well for your design.

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    Expert 2056 points
    So probably we should mimic a CTIA at first, wait a few seconds, see if mic bias comes up, and if not, try OMTP.
  • 0 in reply to Jonathan9420
    TI__Mastermind 45340 points

    Jonathan,

    Yes, I think that is a valid solution if the audio jack configures itself for a 4 pole accessory as situation 1).  

    My concern is situation 2) if the audio jack configures itself to support a 3 pole device grounding both Ring 2 and Sleeve.  We might need to come up with a way to tell the audio jack switch to configure itself as a 4-pole device.  

    For situation number 2) I think this parallels a situation when cell phones using the automatic detecting audio jack switch ICs were trying support selfie sticks.  The audio jacks were detecting the selfie stick as a 3 pole accessory grounding both Ring 2 and sleeve and the selfie stick couldn't communicate a button press back to the phone.  The solution the cell phone makers used was to use the I2C control interface on the audio jack switch to configure the device back to a 4 pole mode.  More information can be found in the app note in the e2e post below.

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    Expert 2056 points
    By the way, do you know of any commercial products these auto-sensing chips are used in that you could mention? It would be good to know how common they are / know of products we could test with.
  • 0 in reply to Jonathan9420
    TI__Mastermind 45340 points
    Jonathan,

    The function these auto sensing products on the audio jack are in almost every major cellphone and notebook. Weather or not the function is provided by a stand alone IC like the TS3A22X or integrated into a codec is up to the cellphone and notebook designers.

    Let me know if that helps.

    Thank you,
    Adam