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TAS5706A distortion at low volume

jian gao1
Prodigy 130 points
Other Parts Discussed in Thread: TAS5706A, TAS5706B, PCM1808

Hello everybody

I discovered a distortion at low volumes at output channels A/B(BTL mode) When testing tas5706EVM2. At higher volumes it works fine.  At this moment output channels A/B is mapped by input SDIN1.  SDIN2 is floating.

How can I resolve it ? Any idea?

  • 0
    TI__Mastermind 34675 points

    Jian,

    What signal level are you considering low volume? THD+N is the ratio of the signal amplitude to the harmonics plus noise. At small signal amplitudes the harmonics are reduced into the noise floor. The THD+N is then dominated by the noise and at that point as your signal gets smaller your THD+N will increase. Here is a snapshot of THD+N vs. Output Power (volume).

  • 0 in reply to Damian Lewis
    Prodigy 130 points

    Hi, Damian

    the voltage level at low volume input signal is 300mv(RMS) and the voltage level at high volume input signal level is 600mv(RMS). The signal is sent by left channel VINL of PCM1808PW whne I tested TAS5706EVM2. The right channel VINR of PCM1808PW is connected directly to gnd.

    the power voltage of output stage of TAS5706A is18V. The output signal amplitude of OUT_A or OUT_B is 4.5v when  input signal is 300mv(RMS).  The signal amplitude of OUT_A or OUT_B is 7v when  input signal is 600mv(RMS). I found that  the distortion of output signal  of OUT_A or OUT_B is bad when  input signal is 300mv(RMS）

  • 0 in reply to jian gao1
    TI__Mastermind 34675 points

    Jian,

    I checked TAS5706B on an EVM and I'm unable to see the distortion you are observing. I'm seeing 0.056% THD+N with 4.5V output and 0.067% with 7V output. I'm using 6ohms load. Can you send me your device register settings, so I can try to reproduce your issue.

    Can you check the supply on the input board with the PCM1808 is correct? I suspect there is a setup issue on the input board that's introducing noise into your input signal.

    Which input board are you using? Is it MC57xxPSIA?