TPA3251: TPA3251

Genie Hsu

Part Number: TPA3251

Dear Sir,

Accordint to TPA3251 datasheet description, it can achieve 175W stereo into 4 ohm in BTL configuration. I don't know how to calculate out the number of 175W.

Best regards,

Genie

over 4 years ago

0 Sam(MPAA) Zhang over 4 years ago

TI__Mastermind 19080 points

Hi Genie,

As a sine wave, the RMS value equals to Vpeak/√2,.

PVDD=36V, Rload = 4Ohm, if there is no clipping, Pout = (36/√2)^2 / 4(Ohm) = 162W. This is ideal output power without clipping. Output power can go higher, but output voltage will be clipped and THD+N get worse.

175W given on datasheet is the typical output power when THD+N=10%. You may refer to figure 3 on datasheet.

Regards,

Hao

0 Genie Hsu over 4 years ago in reply to Sam(MPAA) Zhang

Intellectual 360 points

Dear Hao,

Because it's BTL configuration, shouldn't Vpeak be two times PVDD? That's what I found from Internet.

Best regards,

Genie

0 Sam(MPAA) Zhang over 4 years ago in reply to Genie Hsu

TI__Mastermind 19080 points

Hi Genie,

The AC voltage applied across the loading is a sine wave with Vp=PVDD, Vp-p=2*PVDD. While for a sine wave, the RMS voltage is Vp/√2.

Regards,

Hao

0 Genie Hsu over 4 years ago in reply to Sam(MPAA) Zhang

Intellectual 360 points

Dear Hao,

Could you figure out whta the output power is while operating in single end configuration and 4 ohm load?

Best regards,

Genie

0 Sam(MPAA) Zhang over 4 years ago in reply to Genie Hsu

TI__Mastermind 19080 points

Hi Genie,

For single-end configuration,

If PVDD=36V, Voltage across the speaker slews from 0V to 36V, then Vp=18V, Vrms=18/√2. No clipping max power is (18/√2)^2 / 4= 40.5W.

Regards,

Hao

0 Genie Hsu over 4 years ago in reply to Sam(MPAA) Zhang

Intellectual 360 points

Dear Hao,

According following picture, I have some questions.

1. What kind of audio signal is? Is it a sinusoidal or an analog waveform?

2. What does the audio amplifier output waveform look like when connecting in single-ended configuration?

3. What does the audio amplifier output waveform look like when connecting in BTL configuration?

Best regards,

Genie

0 Sam(MPAA) Zhang over 4 years ago in reply to Genie Hsu

TI__Mastermind 19080 points

Hi,

1. Audio signal can be anything within audio frequency range, including the sine wave.

2. In single-end configuration, the speaker is connected across GND and output. With 36V PVDD, the output can swing from 0 to 36V, making a sine wave with 36Vp-p (18Vp).

3. In BTL, the speaker is connected across OUTP and OUTN. With 36V PVDD, the output can swing from -36V to 36V, making a sine wave with 72Vp-p (36Vp).

Regards,

Hao

0 Genie Hsu over 4 years ago in reply to Sam(MPAA) Zhang

Intellectual 360 points

Dear HAo,

If input is a sinusoidal waveform, does single-ended output a half rectified sine waveform (shown in bottom left) and BTL outout a full rectified sine waveform?

Best regards,

Genie

0 Sam(MPAA) Zhang over 4 years ago in reply to Genie Hsu

TI__Mastermind 19080 points

No, it's sine wave with 1/2 PVDD offset level.

0 Genie Hsu over 4 years ago in reply to Sam(MPAA) Zhang

Intellectual 360 points

Dear Hao,

If input is a sine waveform, no matter it's single-ended or BTL configuration, output waveforms are also a sine wave, right?

With 36PVDD, in single-ended, output is a 36Vp-p sine waveform and BTL output is a 72Vp-p sine wavefrom, Am I understanding correct?

Best regards,

Genie

0 Sam(MPAA) Zhang over 4 years ago in reply to Genie Hsu

TI__Mastermind 19080 points

Hi Genie,

Yes, your understanding is correct. The key point here is in BTL, the output can swing from -PVDD to +PVDD, while in SE, the output can only swing from 0 to PVDD.

Regards,

Hao

0 Genie Hsu over 4 years ago in reply to Sam(MPAA) Zhang

Intellectual 360 points

Dear Hao,

1. If there is a positive input signal (without negative content) feeding into BTL configuration, does the output still swing from -PVDD to +PVDD?

2. if there is a sine wave input signal (including positive and negative content) feeding into SE configuration, due too output can only swing from 0 to PVDD, does that mean the negative content of input signal will disappear on output?

Best regards,

Genie

0 Sam(MPAA) Zhang over 4 years ago in reply to Genie Hsu

TI__Mastermind 19080 points

Hi,

1. No. Positive in, then positive out.

2. The output will swing on both sides of 1/2 PVDD. Positive will be higher than 1/2PVDD, then negative lower than 1/2PVDD.

Regards,

Hao

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TPA3251: TPA3251