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TPA3121D2: TPA3121D2

Part Number: TPA3121D2

I am using TPA3121D2 in single ended configuration with 8 Ohm load.

 I am facing issue if interference of oscillator switching frequency with output signal.

Query 1: Without giving any input at Lin pin, Output at Lout is always showing 1.76V@288kHz switching frequency.

Query 2: When input is given, at that time proper amplification is happening wrt voltage level but still switching frequency noise has been observed on top of output signal.

Please suggest proper filtering elements.

As of now, we have checked with EVM board in that 33uH Inductor and 220nF capacitor is used as output filter.

PFA waveforms for referenceTPA3121D2- Switching Frequency Noise.docx.

  • Hi Meghna,
    So all of your measurement is based on the TPA3121d2 EVM, right? How much is the PVCC voltage? Is there any speaker load on the output? Did you change anything on the EVM board? Where did you probe on the board by the scope? If you probe before the inductor, the output waveform should be PWM squarewave. And if you probe after the inductor, it should be a DC signal if there is no input signal. When you apply 1kHz sinewave on the input, the output should be sinewave, but we can also see very small ripple with around 300kHz PWM frequency. But it's very high frequency components and out of audio band, you don't need to worry much about it.
    If you are measuring on your board, you need to make sure the AMP device is working normallly. 33uH+0.22uF LC filter configuration should be OK.
    Best regards,
    Shawn Zheng
  • Hi Shawn,

    All our measurements are based on EVM only, we haven't modified anything on EVM.

    PVCC voltage is 24 V.

    We haven't connected any speaker load , instead of that directly 8 ohm, 8W resistor is connected at Lout ant GND Pin.

    We have probed output amplified signal after L and Cout at TP3 point through CRO Probe.

  • Hi Meghna,
    From the 3rd and 4th pictures(which I missed yesterday) in your result, the ripple voltage on the output is within the expectation. I don't think that ripple current could degrade the audio performance. If you really want to impress the ripple current, you could try to use larger inductors in the LC filter. Please refer to the following LC filter design document:
    www.ti.com/.../slaa701a.pdf
    www.ti.com/.../slac729
    Best regards,
    Shawn Zheng