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TPA2013D1 290kHz 0-Vcc 50% DC measured at speaker

Hello. I'm using the TPA2013D1RGPR with recommended ferrites and 1000pF caps but the noise at the speaker output is enormous! 50% duty cycle, square wave at 290kHz 4.5Vpp with the input audio grounded (on the far side of the caps). With audio running, the amplifier works great, but on a scope, the audio is swimming in the same 290kHz noise. There is a great deal of ringing on the square wave as well. Although the speaker cannot respond to this frequency, there's some power being wasted and there is a white-noise static hum (very quiet) coming from the speaker. The audio inputs are AC coupled through 1uF, the battery voltage is filtered. I don't see any noise in the audio input. I have a 4 ohm speaker. Any ideas? I'm concerned this won't make it through EMC and may adversely affect battery life. I have SM712-TP ESD diodes on the speaker connector. Gain is set to 6 (float pin 3).

  • Hi, Brett,

    Welcome to e2e, and thanks for your interest in our products.

    What you are seeing is exactly what you should see with a ferrite bead filter.

    Please review the section in the data sheet titled, "FILTER FREE OPERATION AND FERRITE BEAD FILTERS" and let me know if you have any further questions.

    -d2

  • I'm  looking at the data sheet, the section to which you referred me. It does not indicate that I should expect a square wave with a peak-peak voltage equal to Vccin on the audio output pins. This signal is there whether or not the speaker is connected, so I wonder if it may be something independent of the ferrite filter. 

  • Hello Brett,

    The output you are measuring is the expected from the device. Class D amplifiers have a PWM output whose duty cycle varies according the desired audio signal.

    In this document you can find more information about the Filter free operation and a brief abstract of  how Class D amplifiers works.

    Filter-Free™ Class-D Audio Amplifiers

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer