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TPA3136AD2: TPA3136D2 Low frequency noise

Diego Calero
Prodigy 40 points
Part Number: TPA3136AD2
Other Parts Discussed in Thread: TPA3136D2

Iluminado board 2 (2).zip

Hi, 

I'm using The TPA3136D2 on stereo configuration with a single ended input. After connecting the speakers I Noticed a barely noticeable low frequency noise (hum, not 60HZ).

when pressing the shutdown push button the noise disappears with all the audio. I've implemented a volume control pot after the input signal (in my Schematic U3), I suspect this might be causing thermal noise, but I'm  not sure. I'm Using a 4 layer FR4 PCB board (top, bottom, GNDPlane and power plane). I've tried to base my design on the EVM board and the Typical application from the datasheet, the sound overall is good besides this hum when not playing anything. I've attached a zip file with all my altium files and gerber files (Schematic, pcb layout). please help me identify where the noise might be coming from. Due to limited testing equipment I couldn't find the noise frequency on the spectrum analyzer; also my power supply seems to be clean and reliable; and the noise is not coming from the input audio, since is also noticeablewhen the audio jacket is removed. 

  • 0
    TI__Genius 9995 points

    Hi Customer,

    What is your requirement of noise level? Do you have any specific standard for this?  

    As to the control pot after the input signal, can you share more your thinking about this? Further, do you have a TPA3136 EVM board in your hand for correlation?

    We will look into this issue by reproducing it in EVM board, hence, would you please suggest all setting for the reproducing?

    PVDD=?

    load=?ohm speaker?

    gain=?dB and input level =? dBFS?

    other...

    Regards,

    Alix Wan. 

  • 0 in reply to Alix Wan
    Prodigy 40 points

    Hi Alix, 

    PVDD= 13V

    Load= Two 8 ohms 15 W speakers 

    Using a 1 Vpp 5Khz Sinewave:

    Gain= 28dB (20 log(26Vpp/1Vpp))

    input level: 100% (1Vpp)

    Instead of geting the sine wave at the output, I got a weird wave (seems like a square wave) of high frequency 125Khz. 

    find attached here the pictures of the waves 

    Testing.zip

  • 0 in reply to Diego Calero
    Prodigy 40 points

    Also Alix, I don't have a EVM board at hand, we have a required minimum Signal to noise ratio of 80dB. And the thermal noise coming from the pot, comes from the fact that is the only component is not on the EVM board schematic and is known that Pots for volume control introduce a small amount of noise. 

  • 0 in reply to Diego Calero
    TI__Mastermind 19820 points

    Hi Diego,

    You can connect the input pins to GND through 1uF caps, and check if the noise disappear.

    Regards,

    Derek