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implement the TS3A227E without utilizing the I2C port

Ranita Bera
Prodigy 610 points
Other Parts Discussed in Thread: TS3A227E, TS5A22364, TS3A26746E, TS3A225E, TS3A226AE

Customer met an issue on TS3A227E. Since the type-C socket is on a small board, customer wants to put the TS3A227E ic as close as possible to the socket. And due to the limit of the FPC between the main board and the small board, there only could have one signal wire for the switch. And since our TS3A227 is I2C interface, there is no I2C go to the small board. So customer want to use 2 audio switch FSA2275 (Fairchild) to replace it.

 

I talked about they could disconnect the I2C interface, and just to use the auto sense function of 227. But they want us to provide:

  1. If use the default sensing threshold, how many percentage of mic phone could be covered? Is it possible for some headset with mems mic can not be sensed?
  2. What is the purpose for us to have the I2C accessory for change the threshold?

So the mean issue for us is how to convince them our solution is robust, even without the I2C.

  • 0
    TI__Mastermind 45350 points

    Ranita,

     

    The Fairchild FSA2275 is an audio switch similar to TI's TS5A22364.  Both of these switches do not have the automatic Mic and ground switching like TI's TS3A227E.  Does your codec have the mic and ground detection feature and you only need to implement the switching? 

    If you do not need to use the automatic mic and ground detection and switching function I would recommend using the smaller TS3A26746E (1.3mm x 0.8mm) cross point switch.  This device can be controlled with a signal logic select pin but does not have the automatic mic and ground detection feature. 

     

     

    1. If use the default sensing threshold, how many percentage of mic phone could be covered? Is it possible for some headset with mems mic can not be sensed?

    The TS3A227E mic and ground detection algorithm can detect any type microphone as long as these two conditions are met. 

    a) the impedance between the tip and ground is different than the impedance from the tip to sleeve of the heaphone.

    b) the impedance between the tip and ground and tip and sleeve are not both >2.8kohm which is the highest resistance bucket the ADC can recognize.  The TS3A227E will see any impedance >2.8k as the same value declaring the tip to sleeve and tip to ring 2 impedance equal.   You can refer to the post below for more information.

     

     

    2. What is the purpose for us to have the I2C accessory for change the threshold?

    The purpose of changing the Key Press detection thresholds is for devices that would like to support key presses on a headphone like volume control or play/stop.  This feature is described in detail on page 41 of the TS3A227E datasheet. The ADC inside the TS3A227E monitors buttons which looks like a resistor network in parallel with a microphone.  When a user press a button on the mic the resistance of the parallel resistances changes.  The I2C registers can adjust the thresholds the TS3A227E reports back what number button is pressed.



     

    If you do not need this key press detection feature I would look at our TS3A225E device or TS3A226AE (smaller and doesn't have I2C control)

     

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    TI__Expert 3040 points
    Hi Adam,

    TKS for your clarification, it is very clear.

    After we talked with the customer, the only question left:
    1. How could we disconnect all the tips from the ground, so that the SUB pins could be used as the channel information connection, when the headphone is not inserted.
  • 0 in reply to Peter Wei
    TI__Mastermind 45350 points

    Peter,

    I'm not familiar with the channel information connection.  Can you describe which pins you mean by disconnecting "all the tips"?  Maybe a diagram would help make things more clear.

    If you look at the TS3A227E datasheet at the functional table you will see that the default state or Vdd = 0V that there are depletion FETs that turn on the connection of Sleeve and Ring2.  These depletion FETs ground the sleeve and ring2 pins when Vdd is not powered which removes the humming noise that can be created when plugging in an accessory into an unpowered system. 

    The TS3A226AE audio jack switch does not include the depletion FET feature and has the abillity to isolate all signal paths toggling the EN pin.

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    TI__Expert 3040 points

    Hi Adam,

    226 does not have the ground sensing pin, so  will not buy it. local team is convincing for using the IIC to open all the switches.

    But due to the channel information signal is not very low, so is checking with us the capacitance on the RING2 and Sleeve, when all the switch is opened.

    Best Regards,
    Peter Wei

  • 0 in reply to Peter Wei
    TI__Mastermind 45350 points
    Peter,

    Thank you for the update. I'm a little bit confused on the request. Why do you need to know the input capacitance on the Ring 2 and Sleeve pins when the switches are in Hi-Z? Does this effect the audio signal?

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    TI__Expert 3040 points

    Hi Adam,

    Because for the type C plug, the SUB pins are the MIC or Ground pin when it is in the audio accessory mode, but it will be 'channel information' pin when it is in display port mode.

    Since the display port will use the channel information to transmit the digital audio signal, it is up to 192kHz 24bit 7channels. So the speed of the signal is not very low. If they could use the I2C to open all the grounding switches, but if the capacitance of the input pins(tip and sleeve) is too high, it will attenuate the digital signal, to make the eye diagram to be worse, it may cause some error bits of the digital.

    So they are asking about the input capacitance of the input pins(tip and sleeve) when all the sw is off.

    Best Regards,

    Peter Wei

  • 0 in reply to Peter Wei
    TI__Mastermind 45350 points
    Peter,

    Your question is clear to me now, thank you. I will work with our team to provide you with this information.

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    TI__Expert 3040 points
    Hi Adam,

    Do you have any update on it?

    Best Regards,
    Peter Wei
  • 0 in reply to Peter Wei
    TI__Mastermind 45350 points
    Peter,

    I have asked our team about obtaining this characterization data. Unfortunately, when this part was designed this use case was not thought about and the off state capacitance of the switches was not characterized.

    We are looking into a test set up where we can use a capacitance meter with the TS3A227E EVM, but we are not sure if the board capacitance will be significant versus the device capacitance. We may find that we need to explore other options.

    Adam