WM8591GEDSSLASHV datasheet(34/51 Pages) WOLFSON

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WM8591

Production Data

PD Rev 4.0 December 2005

Figure 22 ALC Operation

The gain control circuit is enabled by setting the LCMODE control bit. The user can select between

Limiter mode and three different ALC modes using the LCSEL control bits.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R17 (11h)

0010001

ALC Control 2

LCMODE

ALC/Limiter Select

0 = ALC Mode

1 = Limiter Mode

R16 (10h)

0010000

ALC Control 1

8:7

LCSEL

LC Function Select

00 = Disabled

01 = Right channel only

10 = Left channel only

11 = Stereo

Both the ALC and Limiter functions can operate in stereo or single channel modes. In stereo mode,

the ALC/Limiter operates on both PGAs. In single channel mode, only one PGA is controlled by the

ALC/Limiter mechanism, while the other channel runs independently with its PGA gain set through

the control register.

When enabled, the threshold for the limiter or target level for the ALC is programmed using the LCT

control bits. This allows the threshold/target level to be programmed between 0dB and -22.5dB in

1.5dB steps. Note that for the ALC, target levels of 0dB and -1.5dB give a threshold of -3dB. This is

because the ALC can give erroneous operation if the target level is set too high.

When disabled, the last gain level programmed by the ALC/Limiter will remain stored in the input

PGAs. The desired fixed gain level must then be programmed manually via registers R14 and R15.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R16 (10h)

0010000

ALC Control 1

3:0

LCT[3:0]

1110

(-1.5dB)

Limiter Threshold/ALC Target Level in

1.5dB Steps:

0000: -22.5dB FS

0001: -21dB FS

…

1101: -3dB FS

1110: -1.5dB FS

1111: 0dB FS

hold

time

decay

time

attack

time

input

signal

after

ALC

PGA

gain

ALC

target

level

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