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Class d- audio amplifier

Matt
Prodigy 20 points
Other Parts Discussed in Thread: TAS2505, TAS2110, TAS2562, TAS2780

Hi,

I am looking for advice on a class d audio amplifier BTL configuration.

I need it to drive a purely resistive load. The load is non-linear and can vary between 2-10 Ohms or 4-20 Ohms. 1W.

the output needs to be filtered so there is no/minimal overshoot from the PWM, and the inductors should be as small as possible, so I think a high PWM frequency is needed. I also read that some integrated noise suppression exists.

I will be driving it with a MCU to generate the signal in, so a digital input amplifier may be a nice option.

There are so many options out there I was hoping for some guidance.

Kind regards,

Matt

  • 0
    TI__Genius 13000 points

    Hi matt

    can you give me below information?

    1. what is your pvdd voltage?

    2. what signal be played? music or some certain frequency? 

    3. what is the range for your input signal? max value is 0dBFS?

    4. can your mcu provide i2c signal?

    thanks.

    jesse

  • 0
    Prodigy 20 points

    Hi Jesse,

    Thanks for your response I will try to answer:

    1. PVDD should be as low as possible 3.3V or 5V

    2. it is a fixed frequency, order 16 kHz, the amplitude is modulated at a specific way on the order of dc-2 kHz

    3. this is to be determined, if it is provided by the MCU it will be 0-3V, the output rms ~ 0-2V

    4. Yes, currently I am using an STM32 nucleo.

    note: the load should see a square-wave at ~10-20kHz, with an amplitude that modulates at dc-2 kHz between 1-2V. No overshoot/spikes at the PWM frequency.

    I hope this answers all the questions.

  • 0 in reply to Matt
    TI__Mastermind 34650 points

    Hi Matt

       Let me help you to transfer this Thread to LPA team, they will have suitable device to recommend to you. Our MPA doesn't have Amp support voltage lower than 5V. 

       You could also follow below link to check the product list first.

     https://www.ti.com/audio-ic/amplifiers/products.html

  • 0 in reply to Shadow He
    Prodigy 20 points

    thanks for the transfer to LPA and the list, it is very helpful.

  • 0 in reply to Matt
    TI__Guru* 98235 points

    Hi Matt,

    Based on you requirements, my main concern is your note about the square-wave at ~10-20kHz.
    Our Class-D amplifiers drive a PWM signal switching at ~300kHz, which is duty-cycle modulated based on the input signal amplitude. Usually this PWM switching frequency is filtered (by the speaker itself, or some additional LC or ferrite filter) in order to reproduce audio signals within the 20Hz-20kHz band.
    The switching frequency of the PWM is fixed. Would this be OK for your application?

    Otherwise, you may need to generate the PWM signal itself from the MCU, then buffer/amplify it with an op amp to drive the load. Take into consideration the required slew-rate to reproduce your PWM signal, but given it's a fairly low switching frequency mostly any op amp would do OK.

    Hopefully this helps to better define how to support your application, let me know if you have any questions regarding the first described low power Class-D amplifiers.

    Best regards,
    -Ivan Salazar
    Applications Engineer

  • 0 in reply to Ivan Salazar
    Prodigy 20 points

    Hello,
    The 300kHz or (higher to make filtering easier) PWM is good.

    The difference is that the final output should not be a typical audio sine wave 20-20000Hz, but a wirewove at ~15-18kHz. This frequency would be fixed, the amplitude would be modulated slowly, say squarewave modulation at 1-200 Hz.

    Does that  make sense, is it possible? 

  • 0 in reply to Matt
    TI__Guru* 98235 points

    Hi Matt,

    Usually our Class-D amplifiers drive loads of 4 to 8 Ohms, it seems your load can vary more than that so I would suggest to check TAS2505 as the lowest power and simpler solution, while a boosted amp would help in case the load becomes too high, options for this could be TAS2562, TAS2110, TAS2780.

    In any of these devices I think you may be able to drive a square-wave (even though its not the intended application of an audio amplifier), however for 2562, 2110 and 2780 you should make sure to disable the DC blocking filter.

    By the way, digital input amplifiers interface with I2S or TDM from the host controller. So for the end application I'm not sure if it's worth enabling all that's required for a digital input audio amplifier or just drive the PWM directly from the MCU as mentioned before. Just considering all the options.

    Best regards,
    -Ivan Salazar
    Applications Engineer