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TPA3255: Replacement of TAS5261 with TPA3255DDV – PWM Input Compatibility?

Atefeh Jamshidi
Prodigy 15 points
Part Number: TPA3255
Other Parts Discussed in Thread: TAS5261,

Tool/software:

Hi,

I previously used the TAS5261 in my design, which had PWM inputs. Since it is now obsolete, I plan to replace it with the TPA3255DDV stamp PCB on my motherboard. The obsolete component received PWM input signals generated by the LTC6992-2.

Could you confirm whether the input DC (Input A and Input B) of the TPA3255DDV can operate with PWM signals?

I look forward to your response as soon as possible.

Thank you

  • 0
    TI__Genius 9175 points

    Hi Atefeh,

    The TPA3255 is an analog input part and required DC blocking capacitors on the inputs. You can input a PWM signal, but then your output will be a band limited PWM signal due to the LC filter on the output and the DC block at the input.

    Regards,

    Ramsey

  • 0 in reply to Ramsey Foote
    Prodigy 15 points

    Hi Remsey,

    Thank you very much for your answer.

    If I use an RC low-pass filter instead of the 10µF input capacitor, would that be possible?

    Also, my PWM_A and PWM_B signals—one is a converted version of the other. Would that cause any issues?

    Thanks again for your help.

    Best regards,
    Atefeh

  • 0 in reply to Atefeh Jamshidi
    TI__Genius 9175 points

    Hi Atefeh,

    The purpose of the 10uF is to create a high pass filter not a low pass one. The capacitor on the input is required.

    I am not sure what is meant by a converted version. The TPA3255 can support differential and single ended inputs if that is the question.

    Regards,

    Ramsey

  • 0 in reply to Ramsey Foote
    Prodigy 15 points

    Hi Ramsey,

    Thank you for your response; I really appreciate it.

    I am referring to the PWM signal of the old IC, which is 180 degrees out of phase. I want to replace the old IC with a new one on a stamped PCB. My question is whether the new chip can operate with PWM signal inputs. Should I use an RC or LC filter to convert the PWM signal to an analog signal? If the new chip works directly with PWM, that would be ideal.

    In the new IC, we have different phase options such as 0°, 60°, 180°, etc. If I connect Input A to PWM_1 and Input B to PWM_2 (which is 180° out of phase with PWM_1), will I achieve proper audio output? Additionally, are there any specific concerns regarding M1, M2, or any related configurations?

    I look forward to your response and a summary of your insights.

    Thank youuuuuuu,
    Regards,
    Atefeh

  • 0 in reply to Atefeh Jamshidi
    TI__Genius 9175 points

    Hi Atefeh,

    If the two outputs of the signal are exactly 180 out of phase and after filtering the resulting audio signals are still 180 out of phase, then this will be fine. I would be careful to ensure that the resulting filtered audio signals are 180 out of phase as well and not just time shifted by half of the PWM switching frequency. Other than that, you will still need the DC blocking caps on the input pins to the TPA3255.

    Since you are moving from the TAS5261, I am going to assume that you will be using the device in PBTL operation (M1 is low, M2 is high, inputs C and D pulled low). What you could do is take the PWM output from your modulator and filter it to get the signal. You can then use a single ended to differential converter to generate the differential audio for the inputs to the TPA3255. You can see this circuit on the EVM User's Guide. 

    Regards,

    Ramsey