Cirrus Logic CS42L73 - Manual (Page 44)

44 DS882F1
CS42L73
4.5 Class H Amplifier
The CS42L73 headphone and line output amplifiers use a patent-pending Cirrus Logic Tri-Modal Class H
technology. This technology maximizes operating efficiency of the typical Class AB amplifier while maintain-
ing high performance. In a Class H amplifier design, the rail voltages supplied to the amplifier vary with the
needs of the music passage that is being amplified. This prevents unnecessarily wasting energy during low
power passages of program material or when the program material is played back at a low volume level.
The central component of the Tri-Modal Class H technology found in the CS42L73 is the internal charge
pump, which creates the rail voltages for the headphone and line amplifiers of the device. The charge pump
receives its input voltage from the voltage present on the CS42L73 VCP pin. From this input voltage, the
charge pump creates three sets of the differential rail voltages that are supplied to the amplifier output stag-
es: ±VCP, ±VCP/2, and ±VCP/3.
4.5.1 Power Control Options
The method by which the CS42L73 selects the set of rail voltages supplied to the amplifier output stages
depends on the settings of the ADPTPWR[2:0] bits found in
“Charge Pump Frequency and Class H Con-
figuration (Address 09h)” section on page 85 . There are five possible settings for these bits: Mode 000,
001, 010, 011, and 111.
External Impedance ( ) Maximum Attenuation Possible @ -76 dB Setting (dB)
0 -76.0
1 -74.5
10 -72.3
50 -64.8
100 -60.0
Table 2. Example of Impedance in Reference Path
Referenced Control Register Location
Analog Output
ADPTPWR[2:0]
“Adaptive Power Adjustment” on page 85
Referenced Control Register Location
ADPTPWR[2:0].................... “Adaptive Power Adjustment” on page 85
VCP
+VCPFILT
ADPTPWR[2:0]
+VCP
+VCP/2
Class H Control
S
tep
-d
ow
n/
In
ve
rt
in
g
Ch
ar
g
e P
um
p
CHGFREQ[3:0]
+VCP/3
-VCPFILT
-VCP
-VCP/2
-VCP/3
Figure 17. Class H Operation