CS42L56 datasheet(40/92 Pages) CIRRUS

40 / 92 page

DS851F2

CS42L56

ume setting should be factored in with the volume settings of other control blocks in the signal path.

The Class H controller can be affected by the combined effect of all the volume settings in the relevant

path or the maximum sum in each channel (A, B) and the maximum sum in each amplifier (HP, Line). To

determine the correct rail voltage for the amplifier, the controller assumes the input advisory volume is set

correctly and that the signal level in each processing block does not exceed 0 dB.

General Effect of Volume Sum in Signal Path

If the total gain and attenuation set in the volume control

registers would cause the amplifiers to clip a full- scale

signal when operating from the lower set of rail voltages,

the controller instructs the charge pump to supply the

higher set of the two rail voltages (±VCP) to the amplifi-

ers (at this threshold, the total gain/attenuation has ex-

ceeded -10.5 dB).

If the total gain and attenuation set in the volume control

registers would not cause the amplifiers to clip a full-

scale signal when operating from the lower set of rail

voltages, the controller instructs the charge pump to

supply the lower set of rail voltages (±VCP/2) to the am-

plifiers (at this threshold, the total gain/attenuation is

less than or equal to -10.5 dB).

In order to adjust for external analog (line or microphone sources) or digital (DSP) input volume settings,

the Class H controller also takes into account the settings of the AIN and DIN advisory volume registers.

These volume settings do not affect the volume of the signal but serves to offset the total volume present-

ed to the Class H controller.

Effect of Volume Sum in A or B Path

Since amplifier channels A and B share the same supply, the

controller must consider the volume settings in the path of

both these channels before supplying the appropriate rail

voltage. For any of the three signal paths, the controller will

instruct the charge pump to supply ±VCP to the amplifiers

when the total gain/attenuation of either channel A or B ex-

ceeds the -10.5 dB threshold.

Conversely, the charge pump will supply ±VCP/2 only when

the total gain/attenuation of both channels A and B is less

than or equal to -10.5 dB.

-10.5 dB

Class H

Controller

±VCP/2

±VCP

HP/LINE Supply

Figure 22. Volume Sum Effects

-10.5 dB

case1

case2

Class H

Controller

HP/LINE Supply

Decision:

-10.5 dB

case2

case1

of A

Path =

VCP

VCP/2

of B

Path

Case 1 Result

Case 2 Result

Figure 23. Channel/Amp Effect

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