Class H Amplifier - Cirrus Logic CS42L42 Manual

Based on Fig. 4-13, the formula
Eq. 4-4 can be used to measure the actual mute attenuation based on a measured mute attenuation.
Eq. 4-3 yields a headphone interchannel isolation of +83.5 dB when the following assumptions are made:
= 30 
• R
L
• R = R2 = 12 k
1
= 0.002 
• R
T1
= 0.001 
• R
COM1
= 0.002 '
• R
COM2
Eq. 4-4 can be used to measure the mute attenuation:
Eq. 4-4 yields an actual mute attenuation of –87.77 dB assuming the following:
= 0.4 
• R
T1
• MA (Mute attenuation measured) = –84.8 dB
M
Because large values of R

4.6 Class H Amplifier

Fig. 4-14 shows the Class H operation.
The CS42L42 HP output amplifiers use a Cirrus Logic four-mode Class H technology, which 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 being amplified. This conserves energy during
low-power passages and when the program material is played back at low volume.
The internal charge pump, which creates the rail voltages for the HP amplifiers, is the central component of the four-mode
Class H technology. The charge pump receives its input voltage from the voltage present on either the VCP or VP pin.
From this voltage, the charge pump generates the differential rail voltages supplied to the amplifier output stages. The
charge pump can supply four sets of differential rail voltages: ±2.5, ±VCP, ±VCP/2, and ±VCP/3.
DS1083F2
Eq. 4-3 can be used to measure the headphone interchannel isolation, and formula
Interchannel Isolation
Equation 4-3. Headphone Interchannel Isolation (ICI) Equation
Mute Attenuation
Equation 4-4. Headphone Mute Attenuation Equation
cause increased DC offset (see
T1
ADPTPWR on p. 155
VP_CP
LDO Output
VCP
Figure 4-14. Class H Operation
R + R
COM1 T1

20 log -----------------------------------
= –
  
2 R + R
1 2
 
MA + 6
  
M
---------------------------
R
 

20

--------------- -
= 20 log 10 –

12000

4-13), it is recommended to keep RT1 less than 1 
Fig.
Class H Control
+2.5 V
+VCP
+VCP/2
+VCP/3
–2.5 V
–VCP
–VCP/ 2
–VCP/ 3
4.6 Class H Amplifier
R
COM2
------------------ -
–
R
L


T1
– 6


+VCP_FILT
–VCP_FILT
CS42L42
41