TAS2505EVM: Speaker output waveform

dai_sakamoto

Part Number: TAS2505EVM
Other Parts Discussed in Thread: TAS2505

Tool/software:

The speaker output waveform was output using the evaluation board. The resulting speaker output waveform was a square wave.

Regardless of the volume, the amplitude voltage was ΔV = 9.5V. Isn't this waveform abnormal?

As I understand it, it is a sine wave, as in the sample waveform below, and the amplitude voltage changes depending on the volume.

TAS2505EVM wave↓

DAC 24db

Vol=-0db

yello : spk+

blue:spk -

red : blue - yellow

TAS2505EVM wave↓

DAC =24db

Vol=-10db

Sample(TDA2822 BTL output)　wave↓

yellow : spk+

blue:spk -

red : blue - yellow

over 1 year ago

0 dai_sakamoto over 1 year ago

Intellectual 380 points

Evaluation board conditions

- USB host... USB2.0 (PC connection)

- AVDD1.8V... External power supply used

- SVDD 5.0V... USB power supply used

- Microphone input... Not used

- Headphone output... Not used

- Audio file format... .wav file

Sound quality

case 1 (24db & -0db) ...The sound is loud. The sound quality is poor. Women's voices sound muffled.

case 2 (24db & -10db) ...The sound is normal. The sound quality is good. Women's voices can be heard.

0 dai_sakamoto over 1 year ago in reply to dai_sakamoto

Intellectual 380 points

The waveform is difficult to see, but the waveform from 5 seconds prior is also displayed at the same time.
When I turned up the volume, the ON time of the square wave seemed to increase, and when I turned it down, it seemed to decrease.
I would be grateful if there are any detailed documents regarding the SPK output.

0 Sydney Northcutt over 1 year ago in reply to dai_sakamoto

TI__Mastermind 21210 points

Hello,

What you see on the scope is correct. TAS2505 is a class-d amplifier, so the output is a high frequency PWM signal. Since a speaker acts as a low pass filter, the PWM signal is modulated (duty cycle of PWM is altered) in a way so that signal across the speaker is the input signal times the gain.

The two documents below may be helpful in further explaining this technology.

Technical White Paper How to Choose a Class-D Audio Amplifier (specifically section 7)

Application Report Class-D LC Filter Design

Regarding the poor sound quality, can you share the specs of your speaker? I am wondering if the gain and input level is set too high for the speaker.

Regards,
Sydney Northcutt

0 dai_sakamoto over 1 year ago in reply to Sydney Northcutt

Intellectual 380 points

thanks

It is 8Ω2W. Please wait a moment for the model number.

0 Sydney Northcutt over 1 year ago in reply to dai_sakamoto

TI__Mastermind 21210 points

Hello,

Depending on the audio signal, inputting a full scale audio signal at 24 dB will likely have some clipping, causing audible distortion. I recommend scoping the class-d output through a filter (filter the PWM signal to see the equivalent analog signal) so you can configure the device to where you do not any clipping. At full scale input with 24 dB gain you could also just slowly reduce the digital volume until the distortion is gone.

Regards,
Sydney Northcutt

0 dai_sakamoto over 1 year ago in reply to dai_sakamoto

Intellectual 380 points

model number:2040-8-2M

0 dai_sakamoto over 1 year ago in reply to Sydney Northcutt

Intellectual 380 points

I will configure an LC filter with reference to Table 2 in Class-DLCFilterDesign. How should I calculate to ensure that the rated current and saturation current of the inductor are not exceeded?

0 Sydney Northcutt over 1 year ago in reply to dai_sakamoto

TI__Mastermind 21210 points

Hello,

The saturation current should be rated above the peak current expected. I recommend measuring what the peak current would be for your configuration with the EVM.

Regards,
Sydney Northcutt

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TAS2505EVM: Speaker output waveform