TAS5760LDAPR datasheet(33/77 Pages) TI1

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Digital to PWM

Conversion

Digital

Boost

Volume

Control

Full Bridge

Power Stage

Serial

Audio

Port

Full Bridge

Power Stage

Gate

Drives

Gate

Drives

Digital

Clipper

Closed Loop Class D Amplifier

Digital Gain

(GDIG)

Analog Gain

(GANA)

011010..

Serial

Audio In

PWM

Audio Out

HPF

Interpolation

Filter

SFT_CLIP

1 2 3 4 5 6

TAS5760L

www.ti.com

SLOS782B – JULY 2013 – REVISED SEPTEMBER 2015

Figure 43. Speaker Amplifier Gain Structure

9.4.2.4.1

Speaker Amplifier Gain in Software Control Mode

The analog and digital gain are configured directly when operating in Software Control mode. It is important to

note that the digital boost block is separate from the volume control. The digital boost block should be set before

the speaker amplifier is brought out of mute and not changed during normal operation. In most cases, the digital

boost can be left in its default configuration, and no further adjustment is necessary. As mentioned previously,

the analog gain is directly set via the I²C control port in software control mode.

9.4.2.4.2

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

TAS5760L. 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 to reduce

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

9.4.2.4.3

Recommendations for Setting the Speaker Amplifier Gain Structure in Software 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 analog gain setting via the A_GAIN[3:2] bits in the control port which will produce 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 analog gain.

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