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TPA3110D2 Click and DC fault

Mario Raffin
Expert 2355 points
Other Parts Discussed in Thread: TPA3110D2, AM3352, TPA3110D2-Q1

Dear Support, 

     I already wrote a post on the audio converter forum here, but the problem involves mostly the TPA3110D2, so I would post my question here. 

In my two boards system I have an AM3352 CPU, a AIC3254 codec which drives the TPA3110D2 r with PBTL Output and Single-Ended Input. In the audio converter forum you can see the schematics (R in the PBTL input now is 100K). 

The problem is that when I start a playback, the amplifier emits a loud click. The problem is caused by the difference of bias between the line output of audio codec (800mv) and the input of the amplifier (about 3V).  When the codec output is connected a negative DC step produces a very annoying click at best, a DC fault (recoverable only by a power cycle) at worst.  

What is the correct strategy to avoid this issue?

Thank you. 

mario

  • 0
    TI__Expert 5000 points

    Hi, Mario

              First: try to change your schematic as below:
                

             Second: make sure power up AIC3254 first (with no music playing), then power up TPA3110D2-Q1, then enable TPA3110D2 (Change SD from low to high).

             Third: try to lower the value of C29 and C45, change from 4.7uF...1uF....0.47uF..., and check again.

    The pop is caused by the common mode difference of LOL of AIC3254 and TPA3110D2's input common mode voltage (3.0V). If you use TPA3110D2-Q1's differential input mode, it will be better.

  • 0 in reply to Peter Cao
    Expert 2355 points
    Thank you Pete.
    I tested the TPA3110D2-Q1 in differential mode and this solve the issue. Now there is a very soft "pop" almost not perceptible.

    Since I have to correct my layout, I will include all the changes you suggested. I wonder if something else can be done to improve the result.
    Do you think that, for instance, a middle stage between the output of the codec and the input of the amplifier, with a voltage divider biased to the output voltage of the codec, could be useful?

    Thank you.
    mario
  • 0 in reply to Mario Raffin
    TI__Expert 5000 points
    Hi, Mario
    You can use a voltage divider biased to the output voltage of the codec:
    1) The voltage reference should comes from AIC3254 to minimize the common mode noise differerence.
    2) The divider resistance value. If you do not care about the idle current, you can use smaller resistance, so the RC time constant should be smaller.
  • 0 in reply to Peter Cao
    TI__Expert 5000 points
    Hi, Mario
    The divider should be added on the left side (AIC3254) of 4.7uF capacitor.
  • 0 in reply to Peter Cao
    Expert 2355 points
    I understand. Thank you Pete.