TAS5760L Datasheet, PDF (33/77 Pages) Texas Instruments – Check for Samples: TAS5760L

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Digital Gain
(G_DIG)
TAS5760L
SLOS782B – JULY 2013 – REVISED SEPTEMBER 2015
Analog Gain
(G_ANA)
Serial
Audio In
SFT_CLIP
Serial
Audio
Port
HPF
Digital
Boost
&
Volume
Control
Interpolation
Filter
123456
Digital
Clipper
Closed Loop Class D Amplifier
Digital to PWM
Conversion
011010..
.
Gate
Drives
Gate
Drives
Full Bridge
Power Stage
A
Full Bridge
Power Stage
B
PWM
Audio Out
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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