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TPA3244: mute function

Connie Lu1
Intellectual 2080 points
Part Number: TPA3244
Other Parts Discussed in Thread: TPA3220

Hi team,

My customer is looking to TPA3244 as an alternate to TPA3220, but the dedicated device soft mute (9.4.4 in 3220) is not specifically listed in 3244.  Instead CSTART pin has similar description and timing diagram (11.2 in 3244) and also requires external cap.  Noted the value for the cap may be different from looking at the EVAL board datasheet.

 

I’d like to know if customer can implement the same Mute circuit recommended in TPA3220 datasheet, but connected to C_START pin.  They need this mute feature in the product for TPA3244 to be a true alternate without having to redesign their preamp to handle muting.  Understood 3244 is not a drop-in replacement, but minor PCB update (for a second PCBA ) can make this a viable option for production.

 

Thanks,

Connie

  • 0
    TI__Genius 14480 points

    Hello Connie,

    This would not work as Cmute is different internally. Asserting CMUTE low initiates the device soft mute function. The soft mute function initiates a ramp down sequence of the outputs, and the output FETs go into a Hi-Z state after the ramp down is complete. All internal circuits are powered while in soft mute state. External control of the soft mute function must provide high impedance output when not engaged (open drain output) to allow the CMUTE node to charge/discharge during device ramp up and ramp down when de-asserting and asserting RESET.

    You can't assert C_start it's simply the capacitor that determines device ramp up and ramp down speed so would probably cause audio artifacts.

    best regards,

    Luis

  • 0
    TI__Intellectual 2080 points

    Hi Luis,

    Just following up on this.

    Is there any external controlled mute function that can be done with TPA3244?  Not having this feature creates an issue with the alternate design.

    It isn’t clear to the customer if their previous question was understood in terms of the exact implementation, so they have redrawn it here. The value of the 1k could be adjusted if necessary.  That is the recommended mute function from TPA3220 applied to C_MUTE pin (also with external timing cap). 

    Looking at the power up timing chart (from /RESET set high) for TPA3244 it is quite similar to TP3220 especially the precharge (ignoring 200ms vs 20ms) and the following startup ramp sequence for C_MUTE and C_START pins (both with external timing cap).  If C_START was held low (or forced low) it seemed logical that similar “soft mute” functionality would be possible. 

    If the answer remains “the internal device is different so this won’t work”, could you advise if there is another way that feature could be accomplished with the external control logic signal present (for C_MUTE on 3220) even if the topology needs to change (from the open drain FET).  They could instead externally control /RESET for a mute function but not sure if that would cause other unwanted noise artifacts or issues with input signal still being present at the device input pins.  That was an issue for use with another device TPA3112.

  • 0 in reply to Connie Lu1
    TI__Genius 14480 points

    Hello Connie,

    That external circuit would not work as the internal pin is different, so it would not work.

    The difference between cmute and reset is that while they both initiate a ramp down sequence of the outputs, and the output FETs go into a Hi-Z state after the ramp down is complete. All internal circuits are powered while in soft mute state but during reset internal circuits are shutdown.

    This is different than SD behavior on TPA3112, because the TPA3244 has a rampdown sequence on reset to reduce audio artifacts.

    best regards,

    Luis

  • 0 in reply to Luis Fernandes de Pina
    TI__Intellectual 2080 points

    Hi Luis,

    Do you have a recommendation for implementing a MUTE function?

    At present, customer can only think of setting the device in RESET with the logic signal intended for CMUTE on 3220 while limiting the audio input signal to avoid exceeding the maximum ratings on the input pins, assuming internal biasing is inactive during RESET.

  • 0 in reply to Connie Lu1
    TI__Genius 14480 points

    Hello Connie,

    During reset the internal biasing would be ramped down and inactive since it shuts down the part. No other recommendations besides using the RESET pin and making sure you deal with the inputs during the shutdown state.

    best regards,

    Luis