Cirrus Logic CS42L55 - Manual (Page 31)

DS773F1 31
CS42L55
4.5.3 Efficiency
As discussed in previous sections, the amplifiers internal to the CS42L55 operate from one of two sets of
rail voltages, based upon the needs of the signal being amplified or the total gain/attenuation settings. The
power curves for the two modes of operation are shown in
Figure 15 . This graph details the power sup-
plied to a load versus the power drawn from the supply for each of the three use cases.
When the rail voltages are set to VCP, the amplifiers will operate in their least efficient mode. When the
rail voltages are held at ±VCP/2, the amplifiers will operate in their most efficient mode, but will be will
clipped if required to amplify a full-scale signal.
Note: The ±VCP/2 curve ends at the point at which the output of the amplifiers reached 10% THD+N.
The benefit of Bi-Modal Class H is shown in the solid trace on the graph. At lower output levels, the am-
plifiers operate on the ±VCP/2 curve. At higher output levels, they operate on the ±VCP curve. The dura-
tion the amplifiers will operate on either of the two curves (±VCP/2 or ±VCP) depends on both the content
and the output level of the program material being amplified. The highest efficiency operation will result
from maintaining an output level that is close to, but not exceeding, the clip threshold of the ±VCP/2 curve.
4.6 Beep Generator
The Beep Generator generates audio frequencies across approximately two octave major scales. It offers
three modes of operation: Continuous, multiple and single (one-shot) beeps. Sixteen On and eight Off times
are available.
Note: The Beep is generated before the limiter and may affect desired limiting performance. If the limiter
function is used, it may be necessary to set the beep volume sufficiently below the threshold to pre-
vent the peak detect from triggering. Since the master volume control, MSTxVOL[7:0], will affect
the beep volume, the DAC volume may alternatively be controlled using the PMIXxVOL[6:0] bits.
Class H Amplifiers automatically
switch between ±VCP and ±VCP/2
to conserve power with typical
headphone loads.
Class AB Amplifiers do not
conserve power with typical
headphone loads.
±VCP/2
±VCP
Figure 17. Class H Power to Load vs. Power from VCP Supply
All Supplies= 1.8 V
R
L
= 32
Ω