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TAS2781: Smart Amp Limiting and Characterization

Elliott Robinson
Prodigy 15 points
Part Number: TAS2781
Other Parts Discussed in Thread: TAS5825P, TAS5827

Tool/software:

Hello,

I am working on a small mono speaker with 1 passive radiator. It will use the TAS2781 amplifier. While tuning, we are having issues getting the output level desired from the speaker. We suspect that this may be because of the Smart Amp limiting. We measured the characterization data of the driver using a separate system analyzer (MLSSA) and imported those results into PPC3. However, we don't see an option to change the speaker type from "closed box" to one that accounts for a passive radiator. Additionally, we aren't able to find a combination of smart amp settings that provides the bass response that we are looking for. We have tried changing the protection tuning band crossover points, priorities, and speeds to no real avail. We have been following the Smart Amp Tuning Guide (SLAA751) and its recommendations, but the bass response always reaches its max at about -28dB volume. The other bands keep increasing in volume above this which results in weak bass for those higher volume levels. Here are the excursion estimation verification results from a bass-heavy dance song at low and high volume respectively:

Smart Amp Excursion Low Volume

Smart Amp Excursion High Volume

Are there more smart amp settings that we are missing? And how can we properly account for the passive radiator?

CC:

Thank you,

Elliott R

  • 0
    TI__Guru** 100525 points

    Hi Elliott,

    As you found out only closed box speaker are supported by the protection algorithm. Closed, ported and passive resonator speakers all have different transfer functions. Our algorithm supports a single resonance peak thus ported and passive resonator are not natively supported.
    Can you please share your PPC3 file so we can make some changes? We can try to disable some of the protection features, this is a tradeoff of functionality vs speaker protection.

    Best regards,
    -Ivan Salazar
    Applications Engineer

  • 0 in reply to Ivan Salazar
    Prodigy 15 points

    Hi Ivan,

    Thanks for your response. So to clarify, you are saying that there is no way to configure the Smart Amp protections for anything other than a closed box speaker?

    Here is the PPC file with our current settings. TAS2781 Smart Amp Troubleshooting.zip

    Thank you,

    Elliott R

  • 0 in reply to Elliott Robinson
    TI__Guru** 100525 points

    Hi Elliott,

    That's correct.
    What we can try is relax/disable some of the protection settings so that the algorithm doesn't interpret the effects of the passive resonator as a problem in the speaker. If that works for your application, we can provide an updated PPC3 file during next week with some of these changes.

    Best regards,
    -Ivan Salazar
    Applications Engineer

  • 0 in reply to Ivan Salazar
    Prodigy 15 points

    Okay, I understand. In the meantime, can you suggest an alternative smart amp that is compatible with passive resonator speakers? We would be looking for similar output power.

  • 0 in reply to Ivan Salazar
    Intellectual 255 points

    Ivan,

    Is it true that all "Smart Amp" ICs cannot disable protections completely without operating in ROM mode? ROM mode would eliminate all DSP functionality, such as EQ and dynamics processing?

    The target application for this product is a small portable speaker. Thus efficiency is out top priority, and are looking for a Class-H implementation (or even a Class-Y+Class-H as in the TAS2781) to optimize battery life. However, we cannot give up the DSP functionality either.

    We are very interested in seeing what could be done with the TAS2781 to disable or limit the impact of the smart amp processing while still allowing for us to use the standard DSP functions for tuning. If that is not possible would an amplifier like the TAS5825P allow us to utilize the Hybrid-Pro modulation scheme, Class-H topology, and standard DSP blocks for tuning without the "smart amp" processing? Or do we need to look at an amplifier like the TAS5827?

    Both the TAS5825P and TAS5827 are overkill for our application from a power perspective.

    We look forward to seeing how your tweaks to the PPC3 file impact system output and protections.

    Best,

    Adam

  • 0 in reply to Adam Lock
    TI__Guru** 100525 points

    Hi Adam, Elliott.

    It's true that in order to completely bypass the protection algorithm, the device would have to be operating in ROM mode, we can try some changes also to emulate the algorithm being disabled as listed below.
    What is the speaker power rating? Speaker protection algorithm is mostly used in micro-speaker where it can get easily damaged.

    We'll provide 3 options on PPC3 configuration:

    1. Disabling smart amp protection features that may be affected by passive resonator.
    2. Change the smart amp protection mode from feedback to feedforward mode. This won't use real-time IVsense feedback and would be a similar protection scheme to TAS58xx amplifier.
    3. Disable all smart amp protection features as much as possible (increasing protection limits). You can check if the protection is really needed depending on the speaker rated power.

    I'll get back to you with the new PPC3 file by tomorrow.

    Best regards,
    -Ivan Salazar
    Applications Engineer

  • 0 in reply to Ivan Salazar
    Prodigy 15 points

    Hi Ivan,

    We'd be interested in trying all 3 methods. The speaker output would be 10W.

    Thank you,

    Elliott

  • 0 in reply to Elliott Robinson
    TI__Guru** 100525 points

    Hi Elliott,

    Attached is the updated PPC3 file, you can try the 3 new snapshots with the changes I described before.

    Best regards,
    -Ivan Salazar
    Applications Engineer

    TAS2781 Smart Amp Troubleshooting_TI090424.ppc3

  • 0 in reply to Ivan Salazar
    Prodigy 15 points

    Hi Ivan,

    Thank you for the new settings! We took a look at all the new snapshots, and unfortunately, we weren't able to reach our output targets without going into protection.

    We are now looking at potentially using either the 5825P or the 5827 amps. Our preference would be to use the 5825P due to the Hybrid-Pro algorithm, but we are wary about potentially running into similar issues as the Smart Amp protections on the 2781 amp. Would there be a way to disable any extra protection features that may be present on the 5825P?

    Thank you,

    Elliott

  • 0 in reply to Elliott Robinson
    TI__Guru** 100525 points

    Hi Elliott,

    I'll double check the PPC3 file and share if any more changes can be applied. Regarding TAS582x, I'll discuss that with the responsible engineer, and we may get in a call to discuss further.

    Best regards,
    -Ivan Salazar
    Applications Engineer

  • 0 in reply to Ivan Salazar
    TI__Guru** 100525 points

    Hi Elliott,

    We'll follow up over email. We'd like to better understand the power limitations you're currently experiencing, how we can address these and how other amplifiers may fit in your application.

     Best regards,
    -Ivan Salazar
    Applications Engineer