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Original question:

TPA3128D2: Question for output power and variation of input impedance

TPA3126D2: Can the TPA3126d2 work with 3 ohms load on BTL mode?

Guillermo Sollberger
Prodigy 40 points
Part Number: TPA3126D2
Other Parts Discussed in Thread: TAS5756M, TPA3156D2

Hi,

I have a question regarding this part (TPA3126d2). On my current project, I have to design a BT speaker who needs to drive 2 speakers (1 pair) of 6 ohms each, but it also should be able to drive 2 pairs (first pair in parallel with the second one), if the customer wants it. That scenario will give a 3 ohms load per channel. This part has a minimum load of 3.2 ohms on BTL mode, the question is; can I use it even though it will go a little bit under 3.2 ohms in some cases (when the customer connects 2 pairs of speakers in parallel)?

The audio requirements are:

  • Total Harmonic Distortion (THD+N): 0.1% or less at rated power output
  • Rated Power Output: 25 Watts per channel @ 6 ohms RMS (I chose a 50w/channel amp to make it work more relax, please advice if I can have a less powerful amp)
  • Minimum load impedance: 3 ohms
  • Power supply 22V (I can go up to 24V or 26V if needed, but no more than that) 

If you think this part is not suitable for the purpose, please advise another part.

Best regards,

Guillermo

 

  • 0
    TI__Expert 6720 points

    Hi,

    The main concern while selecting speaker load smaller to spec value is it has risk to trigger Over-Current Protection.

    As for TPA3126d2, the OCP threshold is 7.5A. One question is your system rated power is 25W with 6ohm load, how about the rated output power with 3ohm case?

    If same voltage output to 3ohm, then the rated power goes up to 50W, which means ~5.8A peak. It might have risk to trigger OCP together with inductor ripple current.

    Regards

  • 0 in reply to Matthew Miao
    Prodigy 40 points

    Hi Matthew,

    Thank you for your answer.

    I know the main risk is the OCP and we don't have a final number for power in 3 Ohm load yet, the idea is not to take more power from the amp but to spread more the sound. I guess my question was more about if it is possible to make this amp work on 3 ohms at all, I mean, considering that I can control the output power, for example, adjusting the "power limit" input when you connect 2 speakers in parallel per output or dropping the input volume, will it work?

    The previous project is using the TAS5756M, which can drive 3 ohms load, but I want an analog amp for the new project, and I though the TPA3126d2 would be a good fit. Why the TAS5756M can go according to the datasheet up to 3 ohms if it has the same OCP threshold (7.5A)?

    If the TPA3126D2 it is not the best option to replace the TAS5756M, could you please recommend a better option?

    Best regards,

    Guillermo

  • 0 in reply to Guillermo Sollberger
    TI__Genius 15080 points

    Hello Guillermo,

    The TPA3156D2 has a 10A Overcurrent trip point and can drive up to 70W in a stereo configuration. 

    The minimum load we spec in the datasheet is what we can guarantee works as it's what we tested and validated, loads/system conditions outside the datasheet spec would need to be tested and validated by the customer.

    Best Regards,

    Luis