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TI TPA6011A4 Amplifier Speaker + and - bias voltage unbalance

Other Parts Discussed in Thread: TPA6011A4

Hi,

I use the TPA6011A4 to drive dual 4 ohm speaker.
I understand the DC bias voltage on amplifier bridge output should be same. (Balance)
So no DC current flow through the speaker coil and cause heat.
But my issue is:
The Amplifier Speaker - signal (Pin 12) DC bias is 4.1V
Amplifier Speaker + signal (Pin 14) DC bias is 0.9V
So this DC bias unbalance and cause speaker heat!!

Because this speaker amplifier is a daughter board design (See attached AMP.pdf)

4617.AMP.pdf


and install on one current production MB (See attached MB.PNG).

I find the amplifier input signal (into TPA6011A4 pin 5/9) pull down 22K resistor
(On MB R32 and R33) could cause this problem.
When I remove both, this issue had gone away, Amplifier output DC bias balance.
Speaker work fine.

So my question is why this issue happens
I guess below:
1. Because all Amplifier/OP input signals contain DC bias.
In general, that is 1/2 VDD. If VDD=5V, 2.5V DC bias should be on input pin.
So there is 113uA current flow through this 22K pull down resistor from amplifier
input pin.
Maybe this current too high.
But I did not see this current rating in datasheet.

Please comment, thanks.

Harry Wang
Dec/13/2016

  • Hi Harry,

    Welcome to e2e.
    You might be right in your assumption.
    The input of the device should use only the series ac-coupling capacitor. This capacitor is used to remove any offset voltage from the input signal and let the device to use its own bias voltage.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • Dear Ivan

    Thanks Reply.
    I will remove these 22K pull down resistors and change serial resistor (On MB R42/R44) to 0 ohm as work around.

    Regards,

    Harry Wang
    Dec/16/2016