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Original question:

PCM6240-Q1: MICBIAS over current threshold

PCM6240-Q1: MICBIAS absolute maximum voltage ratings

Shinji Tsuji
Genius 12378 points
Part Number: PCM6240-Q1

Hi team,

How much is the absolute maximum voltage ratings of MICBIAS terminal?

MICBIAS terminal is connected to the microphone input terminal through 1kohm register. 

In my condition, maximum 16V (Vbat) possibly applied to microphone input terminal. 

regards,

  • 0
    TI__Guru 62085 points

    Hello,

    The absolute maximum the MICBIAS pin should be exposed to is 14V.

    The MICBIAS voltage is derived from the internal BOOST converter and is programmable to levels from 5V to 9V.  When the device is operational the highest current flow and worst-case scenario would occur if the MICBIAS is set to 5V and shorted through the 1k resistor to the 16V terminal.  However, the current flow is still only (5V-16V)/1kΩ = 11mA which can the MICBIAS output can sink provided the MBIAS_LOAD register is properly programmed to sink that level of current.  A setting of >20mA is recommended for margin away from the suggested overvoltage short case. 

    The output may get pulled to a level higher than 14V and could be damaged if the setting is on the default 0mA sink current setting as the device will be unable to sink the 11mA of current.

     

  • 0 in reply to Collin Wells
    TI__Genius 12378 points

    Thank you Collin,

    In my other project, MICBIAS resistor is 500ohm, so (16V-9V)/500=14mA. 

    Could you advice if setting MICBIAS_INT_LOAD_SINK_EN to 0d automatically calculate based on device configuration,

    so there is no need to set bit [6:4]?

    regards,

  • 0 in reply to Shinji Tsuji
    TI__Guru 62085 points

    Hi Shinji,

    If using the MICBIAS_INT_LOAD_SINK_EN function then the total sink current will be automatically configured based on the # of channels that are selected.  

    For the internal load sink, the auto setting is enabled by default which takes care of the AC-coupling single-ended input case. Basically depending upon how many AC-coupled single-ended inputs are enabled, accordingly the internal auto logic configure the appropriate load sink value to handle the worst case scenario of sinking required.  So as long as the input channels are activated then the sinking current should be appropriate, but the customer can also set the value directly themselves if desired as well.

    Also note that we have the MICBIAS over-voltage fault detection as well which can be used to auto-shutdown MICBIAS. So, if MICBIAS voltage goes above programmed voltage (by amount of programmed threshold) due to short to higher VBAT voltage on the input pins and not able to sink & regulate then the over-voltage will get triggered.

  • 0 in reply to Collin Wells
    TI__Genius 12378 points

    Hi Collins,

    In my use case, input is DC coupled.

    1.MICBIAS_INT_LOAD_SINK_EN is only applicable to AC coupled input?

    2. If I use MICBIAS_INT_LOAD_SINK_EN under DC coupled condition, how much is the maximum sink capable current?

    3. If over-voltage get triggered and MICBIAS get shutdown keeping 16V applied to MICBIAS through 500ohm resistor, MICBIAS cannot sink current and violate 14V maximum input voltage range which lead to device damage?

    regards,

  • 0 in reply to Shinji Tsuji
    TI__Guru 62085 points

    Hello Tsuji-san,

    1.)  No, it is required for high-swing AC coupled mode but also available for DC coupled mode if required there too. 

    2.)  Because the customer is expecting a particular fault current that needs to be handled we recommend setting the value using the MICBIAS_INT_LOAD_SINK_VAL registers.

    3.)  We are looking into this further but I agree this condition is undesirable and an external clamp may be required.

  • 0 in reply to Collin Wells
    TI__Guru 62085 points

    Hello,

    We had to discuss a little internally on #3.

    #3.) If over-voltage get triggered and MICBIAS get shutdown keeping 16V applied to MICBIAS through 500ohm resistor, MICBIAS cannot sink current and violate 14V maximum input voltage range which lead to device damage?

    After great internal review, it has been determined that it's possible for the MICBIAS pin to get shorted to voltages as high as 18V when disabled due to some inherent internal circuitry.  Therefore, in this application case if the MICBIAS over-voltage is triggered and it is shut down, having it connected to 16V is not an issue.  If the MICBIAS over-voltage shutdown is not enabled and the MICBIAS output remains ON, then the voltage must remain < 14V as previously stated.