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TPA3255: Single-ended for TPA3255 without op amp stage

Lulu Lulu
Prodigy 220 points
Part Number: TPA3255
Other Parts Discussed in Thread: TPA3220,

Hello, i am thinking if i can connect the inputs of the TPA3255 without the op amp stage ensuring that the single-ended signal are converted into balanced connexion? Is it possible to only connect the single-ended connexion to one input channel (by putting a dc blocking capacitor on the input A pin and connect it directly to the main signal source, and the input B pin to a same value capacitor, (like 10uf) but to the tpa3255 ground), like it is commonly done on the TPA3116 ? If i would like to do this, it's to minimize cost and achieve a better sound quality.

Thanks for your response to come.

  • 0
    TI__Mastermind 24835 points
    Hello,
    I think you are asking whether TPA3255 supports single-ended input mode, right?
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    Prodigy 220 points
    Yes, that's it. I would like to know if this chip can support single-ended input mode.
  • 0 in reply to Lulu Lulu
    TI__Mastermind 27880 points
    Hi Lulu,

    Yes the TPA3255 can support a single ended input into the A side for a BTL mode, but you will not be able to get the full output, as you are only providing half the input amplitude of the differential signal.

    Justin
  • 0 in reply to Justin Bohr
    Prodigy 220 points
    Hello, that's not an problem for me, as i don't plan to connect the amplifier to powerfull speakers. But single ended connexion aside, is it possible to create a first order rc crossover by using a resistor and capacitor before the tpa3255's audio inputs to minimize the value of the capacitor (i assume that the input impedance of the amplifier is already making a rc crossover with the capacitor, but, due to the weak input impedance of the tpa3255 chip, it implies to use a relatively high value capacitor of 10uf, that should be electrolytic for cost and proportions reasons, so by making a rc filter, it allow me to use a smaller capacitor like a film one that is better)? But i think that, if i make a rc capacitor before the tpa3255's input, the input impedance of the chip will compromise the total filter operability as, there isn't directly a resistor in paraller to ground in the tpa3255's internal circuit, but most a voltage divider or something alike... So if i do so, i suppose that there will be some noise/pop issues resulting of that ? I am wrong ? Cordially
  • 0 in reply to Lulu Lulu
    TI__Mastermind 27880 points
    Hi Lulu,

    Adding a large RC to try and change the response with the DC blocking cap would significantly reduce the input amplitude to the amplifier. I would recommend using at least a 2.2uF capacitor since this will still give a corner frequency of less than 10Hz.

    Justin
  • 0 in reply to Justin Bohr
    Prodigy 220 points

    So, to be sure, i can without any problems (just i getting a weaker output signal as you sayed) connect the A and D inputs to a single-ended source in BTL mode (A pin to right channel input and D pin to left channel input) and B and C pins to dc blocking capacitors of an equal value than the A and D pins (10uf) to ground (like it is possible with tpa3116 amplifier or tpa3220/3221 amplifiers)?

    Or did i am forced to use a single-ended to differencial output converter made with op amps (that increase the cost and degrade the sound quality but allow me to get the full output power and; maybe depending by the noise floor level of op amps, to get less output noise, because the inputs are differencial)?

    Thanks

  • 0 in reply to Lulu Lulu
    Prodigy 220 points
    Also, there is an little error in the table 5.2 named "TPA3255EVM Board Dimension", where it's writted that the board mesures 140x120mm and where, under the illustration, that the board mesures 160x120, so it is impossible to determine the real mensurations of the board.
  • 0 in reply to Lulu Lulu
    TI__Mastermind 27880 points
    Hi Lulu,

    The correct dimensions are 160x120mm for the TPA3255EVM RevA.

    Justin
  • 0 in reply to Justin Bohr
    Prodigy 220 points

    Ok for the dimensions of the board, to be sure when i design a pcb for the tpa32xx serie chip, i can without any problems (just i getting a weaker output signal as you sayed) connect the A and D inputs to a single-ended source in BTL mode (A pin to right channel input and D pin to left channel input) and B and C pins to dc blocking capacitors of an equal value than the A and D pins (10uf) to ground (like it is possible with tpa3116 amplifier or tpa3220/3221 amplifiers)?

    Or did i am forced to use a single-ended to differencial output converter made with op amps (that increase the cost and degrade the sound quality but allow me to get the full output power and; maybe depending by the noise floor level of op amps, to get less output noise, because the inputs are differencial)?

    Thanks