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TAS2562YFPEVM-DC: More power efficient switching? Turn off "smart" features

Zach Karlsen
Prodigy 10 points
Part Number: TAS2562YFPEVM-DC
Other Parts Discussed in Thread: TAS2562, TAS2563

We are testing the TA2562 EVK. I am inputting a 1khz sine wave. An analog amplifier would pwm this signal when trying to decrease output voltage instead of trying to average by switching rails. I will share pictures below for better explanation. 

Below is the PWM output of a 1khz sine wave measured across the leads of a 4Ω driver. Within the blue boxed region, the sine wave is ramping down in voltage and switching over to the negative rail. This happens again in the green section.

Instead of changing the PWM duty cycle to achieve the desired output, the amplifier is trying to average both positive and negative rails to achieve this voltage. This results in a power loss for the system and at louder volumes it seems to struggle to keep up. Is there any way to configure this for better power savings?

Below is the analog amp for comparison:

  • 0
    TI__Mastermind 19465 points

    Hi Zach,

    what you are seeing here is the LSR modulation scheme used in our low power Class-D amplifiers, the other amplifier you referenced appears to be BD modulation. it is 'hard wired' in the analog of the device and therefore cant be disabled. 

    as BD modulation will be switching at 50% duty cycle when there is no audio the LSR will be switching at <2% duty cycle. this will give decreased idle power consumption which is very desirable for battery powered apps that this part was targeting. this minimal duty cycle will also reduce the power dissipated in any LC filter populated on the amplifier output.

    I would also give some push-back that it is affecting the efficiency of the device. TAS2562 is approaching 90% efficiency at full power, which for its time is very competitive. 

    It sounds like you may be running into some other issue, can you explain more when you say it is struggling to keep up?

    Regards,
    Arthur

  • 0 in reply to Arthur Brown
    Prodigy 10 points

    Hi Arthur,

    Thanks for the quick reply.

    What we are seeing is that the original PWM signal reaches up to the boosted ~11V. As we increase the volume, the duty cycle increases but the output voltage decreases. This leads to the volume not actually increasing and the speaker not getting substantially louder as it is not being driven above ~4.5V at full volume. Watching a low pass filtered output shows the sine wave not exceeding 4.5V at maximum volume - not close to the boosted voltage.

    Again thanks for the help.

    Best,

    Zach

  • 0 in reply to Zach Karlsen
    TI__Mastermind 19465 points

    Hi Zack, 

    You are playing audio through the EVM via USB  connection correct? Just want to make sure it is not an issue with external I2S settings

    is the output clipping? for 4Ohms this this device is able to deliver 6.1W @1%, THD, that should be about 7 Vpeak., or 4.9Vrms, Is your 4.5V number rms or peak? is the PVDD voltage dropping?

    Otherwise the device could be limiting the output for other reasons, I am not sure if you have changed any settings in the PPC3 GUI, but other features that could affect the output level are;

    - Volume control (should be 0dB)

    - limiter 

    - Brown out protection BOP

    - Thermal foldback 

    - Amplifier Level (Default is 16dBV)

    These settings can be found in the "device control" panel in the GUI. 

    Regards,
    Arthur

  • 0 in reply to Arthur Brown
    Prodigy 10 points

    Hi Arthur,

    Yes we are having quite a bit of capacitance on PVDD and its holding steady. 

    Does the TAS2562 input the model into the amp? If so is there a way to remove that so we can have an essentially "dumb" amp. And then we will slowly turn these features back on as we develop for them.

    We are also boosting up to 11V. I realize that 6.1W will deliver the 7V peak continuous - but can it not get higher than 7V for small durations like at the peak of the wave?

  • 0 in reply to Zach Karlsen
    TI__Mastermind 19465 points

    Hi Zach, 

    TAS2562 has no DSP so there is no model(assume you mean speaker model, such as that used in TAS2563)

    the features i listed above are what would be able to affect the output. if you disable all of these do you still see that the output is limited. 

    and yes, the output should be able to exceed the 7Vpeak. this is just the point where the THD starts to degrade significantly. if you disable all the mentioned features, and set the "amplifier level' to its max value and volume control to 0dB, do you still see the limited votlage?

    Regards,

    Arthur