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TAS6424M-Q1: output power vs vbatt input range

Chris Yao1
Prodigy 70 points
Part Number: TAS6424M-Q1

I am working on a car infotainment design with Vbatt ranges from 6V to 16V.

I do not want to add a buck-boost converter to maintain a fix voltage supplying to the speaker amplifier considering the board area and power dissipation increase.

I am wondering if there is a good correlation (plot) between output volume level and input vbatt voltage.

And if the audio volume change is noticeable when vbatt swings 3Vpk-pk, 2Vpk-pk, or 1Vpk-pk.

It will be great if you can recommend me the industry practice for the voltage supply to the speaker amp.

thanks,

Chris

  • 0
    TI__Mastermind 22850 points

    Hi Chris,

    I think we've got a graph in the datasheet that's similar to what you are looking for. The graph that's shown below is for 2.1MHz. But we also have another one for 384kHz, though they are both quite similar. Also note that this is for 10% THD. 

    While 10% THD is considered to be "hard" clipping, what's an important take away here is that the as you go up in voltage, the amount of output power is higher for when you reach 10% THD. This is due to the fact that we design our class-D amplifiers to reach voltage clipping before overcurrent. 

    Let me know if this helps clarify things for you.

    Best Regards,

    Robert Clifton

  • 0 in reply to Robert Clifton56
    Prodigy 70 points

    Thanks, Robert.

    I am looking for power vs speaker loudness plot.

    I am wondering how much differences in power level is considered noticeable in terms of loudness. 

    From the supply voltage vs power plot, if the car battery dropped from 12V to 11V, there will be about 3-4W power drop. I would like to know how that translates to loudness.

    I understand it will depend on the audio source and the volume I am playing and also speaker frequency response, but I wonder if there is any rule of thumb for this.

    Do you also have any recommendation on the automotive industry practice for the voltage supply to the speaker amp. I am still debating if I want to add a buck-boost to maintain a fixed volume.

    regards,

    Chris

  • 0 in reply to Chris Yao1
    Prodigy 70 points

    (I accidentally clicked 'This resolved my issue', so I copied my last reply here)

    Thanks, Robert.

    I am looking for power vs speaker loudness plot.

    I am wondering how much differences in power level is considered noticeable in terms of loudness. 

    From the supply voltage vs power plot, if the car battery dropped from 12V to 11V, there will be about 3-4W power drop. I would like to know how that translates to loudness.

    I understand it will depend on the audio source and the volume I am playing and also speaker frequency response, but I wonder if there is any rule of thumb for this.

    Do you also have any recommendation on the automotive industry practice for the voltage supply to the speaker amp. I am still debating if I want to add a buck-boost to maintain a fixed volume.

    regards,

    Chris

  • 0 in reply to Chris Yao1
    TI__Mastermind 36695 points

    Hi Chris,

    You will  not notice a volume change when the battery voltage changes.  There is feedback in the amplifier that controls the gain.  Therefore, you will not notice a change in loudness.  Maximum power output is changed due to clipping.  You will not hear a volume change, but more distortion when playing a clipped levels. 

  • 0 in reply to Gregg Scott
    Prodigy 70 points

    Hi Gregg,

    Thank you for clarifying.

    Can you elaborate a bit more on how does this feedback in the amplifier and gain control work if the battery voltage level increases or drops? 

    It sounds like there is an automatic gain controlled block in the amplifier and the gain is calculated based on the set gain and speaker output power (battery voltage and current). Is this correct? 

    For our application, 9V-16V operation condition, what will be the suggested clipping voltage?

    regards,

    Chris 

  • 0 in reply to Chris Yao1
    TI__Mastermind 36695 points

    Hello Chris,

    This is the foundation of feedback theory in amplifiers.  This is not the venue to teach feedback theory. 

    There is no AGC to control the amplifier over power supply voltage. The gain is fixed by the internal feedback look in the TAS6424M-Q1

    The clipping voltage will be the power supply voltage.  This is the limit of the amplifier voltage.  In a full bridged amplifier, with a power supply of 9Vdc will have a clipping voltage of +/-9V max.  And at 16Vdc, the maximum output voltage is +/-16V max.