Cirrus Logic CS42L55 - Manual (Page 27)

DS773F1 27
CS42L55
4.5 Class H Amplifier
The CS42L55 headphone and line output amplifiers use a patented Cirrus Logic Bi-Modal Class H technol-
ogy. This technology maximizes operating efficiency of the typical Class AB amplifier while maintaining 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 Bi-Modal Class H technology found in the CS42L55 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 VCP pin of the CS42L55. From this input voltage,
the charge pump creates the differential rail voltages that are supplied to the amplifier output stages. The
charge pump is capable of supplying two sets of differential rail voltages. One set is equal to ± VCP and the
other is equal to ± VCP/2.
4.5.1 Power Control Options
The method by which the CS42L55 decides which set of rail voltages is supplied to the amplifier output
stages depends on the settings of the Adaptive Power bits (ADPTPWR) found in
“Class H Power Control
(Address 06h)” section on page 45 . As detailed in this section, there are four possible settings for these
bits: Mode 00, 01, 10 and 11.
Referenced Control Register Location
Analog Output
ADPTPWR[1:0]
CHGFREQ[3:0]
PDN_HPx[1:0]
PDN_LINx[1:0]
HPxMUTE
HPxVOL[7:0]
LINExMUTE
LINExVOL[7:0]
ANLGZC
PLYBCKB=A
HPxMUX
LINExMUX
“Adaptive Power Adjustment” on page 45
“Charge Pump Frequency” on page 67
“Headphone Power Control” on page 43
“Line Power Control” on page 43
“Headphone Channel x Mute” on page 57
“Headphone Volume Control” on page 57
“Line Channel x Mute” on page 58
“Line Volume Control” on page 58
“Analog Zero Cross” on page 46
“Playback Channels B=A” on page 50
“Headphone Input Select” on page 47
“Line Input Select” on page 47
Referenced Control Register Location
ADPTPWR[1:0] ................... “Adaptive Power Adjustment” on page 45
+VHPFILT
-VHPFILT
HPOUTA
HPOUTB
HPREF
ADPTPWR[1:0]
+VCP
+VCP/2
-VCP
-VCP/2
VCP
LINEOUTA
LINEOUTB
LINEREF
HPxVOL[6:0]
HPxMUTE
ANLGZC
PLYBCKB=A
LINExVOL[6:0]
LINExMUTE
ANLGZC
PLYBCKB=A
HPxMUX
LINExMUX
from PGAx
from DACx
PDN_HPx[1:0]
PDN_LINx[1:0]
HP Detection HPDETECT
= HP and Line Supply
+HP Supply +Line Supply
-HP Supply -Line Supply
Class H Control
S
tep
-d
ow
n
/In
v
e
rt
in
g
C
h
ar
ge
Pu
mp
CHGFREQ[3:0]
Figure 13. Analog Output Stage