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LM4766: Power Consumption at Mute Mode

Part Number: LM4766

Dear Specialists,

My customer is testing LM4766T and has a question.

I would be grateful if you could advise.

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(1)When muting, the consumption current of A amplifier A / B is about 21 mA flow, power consumption of about 1.2 W occurs.

At this time, the consumption current of the intermediate voltage generation circuit around Q47 is about 0.8mA and the audio input is shorted at 100 Ω 

And then, the amplifier A is active and input a sine wave of 660 Hz 0.100 V p-p, the amplifier A consumes about 120 mA, resulting in total power consumption of 4.536 W.

Are these power consumptions normal as LM4766T? I feel that the power consumption is large especially when muting

Please let me know if there is a way to reduce power consumption because there is a contract of space and the size of heat sink is limited.

(2) Since the amplifier B is not used, we want to minimize the current consumption.

Is there a problem with connecting the intermediate voltage (13.82 V) to GND_B and connecting the divided voltage (13.98 V) to + IN_B to make it a voltage follower?

In order to enter mute mode, the mute pin is open.

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I appreciate your great help in advance.

Best regards,

Shinichi

  • Hi Shinichi-san,
    As I mentioned in another post, the support for this device is very limited. I can't replicate your measurement on the board, because EVM is not availablle any more. I'm trying to analyze this by the datasheet data. The datasheet shows that the quisecent current is typically 48mA and can reach 100mA max value. So your consumption current result looks reasonable. If amp B is used, I think you can set it to mute mode directly. Your usage about voltage follower is not the recommended circuit, so I'm not sure the stability and reliability.
    Best regards,
    Shawn Zheng
  • Hi Shawn,

    Thank you for your reply.

    I understand the supply current  is reasonable,

    LM4766 is quite large power consumption, due to it's an old devise, I think.

    I'll share this information with the customer.

    I appreciate your great help.

    Best regards,

    Shinichi

  • Hi Shawn,

    The customer has an additional question.
    He'd like to know how to reduce current consumption at Mute.

    Could you please advise?

    ---
    Since the amplifier B is not used,
    Connect an intermediate voltage (13.82 V) to GND_B and connect a divided voltage (13.98 V) to + IN_B
    It is a voltage follower.
    Is there any problem with this design?

    I'd like to minimize current consumption of Amp_B at Mute.

    ---

    As you mention before, voltage follower is not recommended I think.
    Could you please advise the good way the pin configuration and reducing current consumption at Mute.

    I appreciate your great help.

    Best regards,
    Shinichi
  • Hi Shinichi-san,
    Sorry for the late reply because I was out of office for biz travelling. I understand that the idle current consumption for this device is high, because itis a very old product. I don't think there is the other way to decrease the idle current further in mute mode. I'm sorry that the support for this device is very limited.
    Best regards,
    Shawn Zheng
  • Hi Shawn,

    Thank you for your reply.

    I understand that the support is limited.

    I'll share with the customer.

    I appreciate your great help.

    Best regards,

    Shinichi