TAS5760M datasheet(39/66 Pages) TI

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TAS5760M

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SLOS772B – JULY 2013 – REVISED JULY 2013

Considerations for Setting the Speaker Amplifier Gain Structure

Configuration of the gain of the amplifier is important to the overall noise and output power performance of the

TAS5760M. Higher gain settings mean that more power can be driven from an amplifier before it becomes

voltage limited. Moreover, when output clipping "at the rail" is desired, it becomes important that there be enough

voltage gain in the signal path to drive the output signal above the PVDD level in order to "clip" the output signal

at the PVDD level in the output stage. Another desirable aspect of higher gain settings is that the dynamic

headroom of an amplifier is increased with higher gain settings, which increases the overall dynamic audio

quality of the signal being amplified.

With these advantages in mind, it may seem that setting the gain at the highest setting available would be

appropriate. However, there are some drawbacks to having a gain that is set arbitrarily high. The first drawback

is that a higher gain setting results in increased amplification of any noise that is present in the signal path. If the

gain is set too high, and the speaker is sensitive enough, this may result in an audible "hiss" at the speakers

when no audio is playing. Another consideration is that the speakers used in the system may not be rated for

operation at the power levels which would be possible for the given PVDD supply that is present in the system.

For this reason, it may be necessary to limit the voltage swing of the amplifier via a lower gain setting in order to

reduce the voltage presented, and therefore, the power delivered, to the speaker.

Recommendations for Setting the Speaker Amplifier Gain Structure in Hardware Control Mode

1. Determine the maximum power target and the speaker impedance which is required for the application.

2. Calculate the required output voltage swing for the given speaker impedance which will deliver the target

maximum power.

3. Chose the lowest gain setting via the SPK_GAIN[1:0] pins that produces an output voltage swing higher than

the required output voltage swing for the target maximum power.

NOTE

A higher gain setting can be used, provided the noise performance is acceptable and the

power delivered to the speaker remains within the safe operating area (SOA) of the

speaker, using the soft clipper if necessary to set the clip point within the SOA of the

speaker.

4. Characterize the clipping behavior of the system at the rated power.

–

If the system does not produce the target power before clipping that is required, increase the gain setting.

–

If the system meets the power requirements, but clipping is preferred at the rated power, use the soft

clipper to set the clip point

–

If the system makes more power than is required but the noise performance is too high, consider

reducing the gain.

5. Repeat Step 4 above until the optimum balance of power, noise, and clipping behavior is achieved.

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TAS5760M Datasheet(PDF) 39 Page - Texas Instruments