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TPA3221: Startup issue

Part Number: TPA3221

Hi TI support team,

 we found an issue that TPA3221 cannot start up without  PWM output.

Schematics below

Summary of the test 

  • We connected IN1_M and 1N2_M in the circuit and used a common cap, does it impact the performance of the amp?
  • There is the current source in IN1_P/ IN1_M /IN2_P /IN2_M and charge to these AC couple cap when amp startup, does it relevant to the previous item?
  • We did some changes in the circuit and sequence of power, the test result is in the following for you to reference.


 When the problem occurs, the waveform as shown below

  • Test of issue: IN1_P goes down to 0 and no PWM output



  • Change R23, R141 to 47K, and R32, R86 to 100K
  • Amp startup with PWM output and IN1_P trigger to 5.4V and change to 2.48V after reset pull up, need to test to check the performance


 Please advise what is the problem of the circuit and would you provide the explanation and solution to this startup issue. Thanks




  • Hi Kelvin

       During startup, our device need to set up the DC bias for all the input pins, connect both IN-M together may causing problem. I suggest to cut out this connection between two IN_M and have a check.

      Also please check the FAULT and OTW_CLIP pin condition for helping judge if there's any other problems.

  • Hi  Shadow,

    There are not fault signals ( FAULT or  OTW_CLP ) has been  detection when the AMP is not startup. But changing the bigger AC coupling capacitors to AMP can wake up..

    -Change the AC couple cap of C-final power board to C2 value(C29,C35,C36,C41---47uf  C171,C175---100uf) and amplifier start up with PWM output.

    P.S. we are using the external 5V DCDC circuit to drive the VDD of the AMP and there are some delayed between the PVDD ( +25V ) and VDD (-5V)

    The startup issue seem to be relative to the bias voltage , VDD and reset timing. Please further advise and thanks.

  • Hi Kelvin 

        The sequence seems no problem.

        But the input side capacitor all seems very large, also the IN_M side connection can't guaranteed by us. 

        We only suggest 1uF capacitor placed at both IN_P and IN_M.