WM8980_07 datasheet(41/112 Pages) WOLFSON

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Pre-Production

WM8980

PP Rev 3.1 March 2007

ALCMODE

Determines the ALC mode of operation:

0=ALC mode

1=Limiter mode

Decay (gain ramp-up) time

(ALCMODE ==0)

Per

step

Per

6dB

90% of

range

0000

410us

3.3ms

24ms

0001

820us

6.6ms

48ms

0010

1.64ms

13.1ms

192ms

… (time doubles with every step)

0011

(13ms/6dB)

1010

higher

420ms

3.36s

24.576s

Decay (gain ramp-up) time

(ALCMODE ==1)

Per

step

Per 6dB

90% of

range

0000

90.8us

726.4us

5.26ms

0001

181.6us

1.453ms

10.53ms

0010

363.2us

2.905ms

21.06ms

… (time doubles with every step)

7:4

ALCDCY

[3:0]

0011

(2.9ms/6dB)

1010

93ms

744ms

5.39s

ALC attack (gain ramp-down) time

(ALCMODE == 0)

Per

step

Per 6dB

90% of

range

0000

104us

832us

6ms

0001

208us

1.664ms

12ms

0010

416us

3.328ms

24.1ms

… (time doubles with every step)

0010

(832us/6dB)

1010

higher

106ms

852ms

6.18s

ALC attack (gain ramp-down) time

(ALCMODE == 1)

Per

step

Per

6dB

90% of

range

0000

22.7us

182.4us

1.31ms

0001

45.4us

363.2us

2.62ms

0010

90.8us

726.4us

5.26ms

… (time doubles with every step)

R34

ALC Control

3:0

ALCATK

[3:0]

0010

(182us/6dB)

1010

23.2ms

186ms

1.348s

Table 20 ALC Control Registers

When the ALC is disabled, the input PGA remains at the last controlled value of the ALC. An input

gain update must be made by writing to the INPPGAVOLL/R register bits.

MINIMUM AND MAXIMUM GAIN

The MINGAIN and MAXGAIN register sets the minimum/maximum gain value that the PGA can be

set to whilst under the control of the ALC. This has no effect on the PGA when ALC is not enabled.

PEAK LIMITER

To prevent clipping when a large signal occurs just after a period of quiet, the ALC circuit includes a

limiter function. If the ADC input signal exceeds 87.5% of full scale (–1.16dB), the PGA gain is

ramped down at the maximum attack rate (as when ALCATK = 0000), until the signal level falls

below 87.5% of full scale. This function is automatically enabled whenever the ALC is enabled.

WM8980 Datasheet(PDF) 41 Page - Wolfson Microelectronics plc

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