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TPA2012D2: Speakers are Buzzing at 300Khz

Michael Haire
Prodigy 20 points
Part Number: TPA2012D2

Hello
I am working on an amplifier circuit, but when I power on and enable the amplifier with no input to the left and right channels. my speakers begin buzzing like a beehive. I have connected the oscilloscope to the speaker and found that the buzzing is at 300kHz which is the same switching frequency as the TPA2012. I have attached a screenshot of the schematic and the layout of the amplifier circuit.



The circuit employs a continuous ground plane and I am routing my analog and digital in separate areas so they should not be crossing with each other. (The Orange outline is my analog power plane) Analog power is being supplied by my DC power supply through a ferrite as a filter. 


Here is my oscilloscope waveform

Is this behavior correct due to the PWM used by Class D amplifiers? Is this something that will always happen if the amplifier is enabled with no audio input, or is there something wrong with my circuit that I could improve?

  • 0
    TI__Guru** 100525 points

    Hi Michael,

    Can you please show what is the connection for the unused IN+ pins? Seems you short them together and then across a couple passive components to GND. Please note you should have individual AC coupling capacitors to GND.

    You have R in series and C to GND at IN- pins, note these should also be AC coupled using a series capacitor as the first component that IN- sees, you can connect RC filter after the AC coupling capacitors.

    You may test by removing R13 & R14 and check if noise improves, this may tell if noise is coupling in from the audio source.

    The 300kHz switching itself shouldn't be a problem, it's the duty cycle jittering caused by input noise what's producing the noise at the speaker.

    Best regards,
    -Ivan Salazar
    Applications Engineer

  • 0 in reply to Ivan Salazar
    Prodigy 20 points

    Thank you for your assistance
    I disconnected both inputs from the amplifier and that resolved the buzzing, then I replaced R13 and R14 with a 1uF capacitor and that was able to resolve my buzzing but still allowed sound to play. I will just need to go fully update my schematic with series capacitors