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LM3886 mute control

Torje Nikolai Thorsen
Intellectual 520 points
Other Parts Discussed in Thread: LM3886

Hi,

I am using the LM3886 chips for an active speaker with logic operated mute control.

Two LM3886 chips are used in each speaker, and I need to mute/unmute both chips simultaneously. I would like to connect the mute pins (pin 8) of each of the two chips, in order to control them using one common MOSFET switch (with a series resistor on its low side) instead of two. I have simulated a muting circuit drawing 1 mA through a common MOSFET switch when in unmuted mode (theoretically 0.5 mA from each chip). As I do not know exactly how the internal circuitry of the chip looks like, I am not able to predict the impact of doing this. I am afraid this solution may not guarantee an equal repartition of the two currents, ending up with one chip muted and the other not. For all I know, a such connection between two chips may cause crosstalk related problems as well.

Can anyone tell me if this solution is reliable, or if I rather should use separate switching devices for each chip? Can I rely on pin 8 having a potential of -2.6 V?

Best regards,
Torje

  • 0
    TI__Expert 3840 points

    Hi Torje,

    Yes, you can connect the two mute pins together and control them simultaneously. All you need to have is a constant current of n times 0.5mA where n is the number of ICs. As an example, if we had a constant voltage of -10V connected through a 7.4k ohm resistor to both IC mute pins, we would have 10V - 2.6V = 7.4V across 7.4k ohms or 1mA of constant current. That 1mA will take care of both devices. Please note that the current is being drawn out of the pins and is negative, so the 10V is actually -10V wrt ground.

    The equivalent schematic on page 7 exemplifies the mute circuitry very well. It is essentially 3 diode drops and a 1k resistor. When current is pulled out of the mute pin, the input differential pair is switched over to a second differential pair, completely disconnecting the input from the output.

    There shouldn't be any concern of crosstalk between the devices.

    I hope this helps.

    Best Regards,

    JD

  • 0 in reply to John De Celles
    Intellectual 520 points

    Hi John,

    Thank you very much for your fast response.

    Best regards,
    Torje