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AB-Class vs. D-Class

Pascal Drecker
Prodigy 30 points
Other Parts Discussed in Thread: PCM1782, TPA701, TPA6205A1, TAS5342

Hi,

I like to drive a mini speaker (0.3 W nominal, 0.5 W maximal, 8 ohm) after the PCM1782 (mono). It's my first audio application and I am not sure which amplifier I should use. AB-class or D-class?

TPA701, TPA2031, TPA2036 or another one?

I have a single 5V power supply for USB-Bus and audio. The ground plane is also used for a 32-Bit MCU with DDR2-RAM. Should I build an ground island and connect it on an single point through an ferrite bend?

My application is not portable!

Regards,
Pascal

  • 0
    TI__Genius 16645 points

    Hello Pascal:

    Based on what you have written, I would suggest the TPA6205A1.

    It is an mono AB amplifier and should do a good job in your application.  I like it for this type of application because the input and feedback resistors are external and I then have control over gain and frequency response.

    Do you need volume control?

    Please let us know more about your application and perhaps we have a product offering that will be an even better fit for your requirements.

    Grounding is always an interesting subject. and it depends on your performance requirements.  I assume that you will have a ground plane for your MCU and memory and that will be your main power ground plane.  You do not need a separate ground island for the power amplifier as long as you do a good job with your PCB routing and ground plane pour .  You will probably need an island for your DAC.  Hopefully, you can drive the input to the power amplifier differentially and that will help, too.

    Rgds,

    Fred

  • 0 in reply to Fred Shipley
    Prodigy 30 points

    Hello Fred,

    thanks for your reply. The TPA6205A1 looks very nice.

    For a signature card reader I like to replace an silly buzzer with an speaker to generate mono sound effects like 'key pressed'.

    As I can save my sound effects with different loudness the volume control is not a must have. As the MCU has an very flexible I2S interface, I can nearly use any DAC.

    Unfortunately my application is very cost sensitive.

    Rgds,

    Pascal

  • 0 in reply to Pascal Drecker
    TI__Genius 16645 points

    Hi Pascal:

    It sounds like you have your sounds memory mapped.

    Can you encode them as PWM instead of PCM and then clock them out of a GPIO pin?

    Then, if you put a simple RC integrator in front of the TPA6205A1 (and limit its high end frequency response) you could possibly eliminate the DAC entirely.

    Rgds,

    Fred

  • 0 in reply to Fred Shipley
    Prodigy 30 points

    Hi Fred,

    Yes, my sounds are memory mapped.

    Unfortunately the Coldfire MCF54453 (266 MHz) has no PWM module. Implementing the PWM signal in Software the CPU usage will be properly too high. What do you think?

    Even though my next project will have an Coldfire with a PWM module. So I will try the PWM method in any case.

    Rgds,

    Pascal

  • 0
    Prodigy 20 points

    hi fred,

    I am looking for the class D amplifiers "group delay" spec table measurement .

  • 0 in reply to fatih çöl
    TI__Genius 16645 points

    Hello Fatih:

    Good question.  Our digital input power stages (the TAS5342 for example), have only the delay associated with the switching time, around 200nS.  The are driven by a digital PWM modulator which has about a 2 sample delay.  However, our pwm modulators also have signal processing features like digital filter.  You will have a delay through the filter based on the response that you program into the filter.  The anlog input Class D also has a very low latency.  In both cases the latency is dominated by the cutoff frequnecy of the output filter.

    Rgds,

    Fred