WM8978CGEFLSLASHV datasheet(39/118 Pages) WOLFSON

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Production Data

WM8978

PD, Rev 4.5, October 2011

LIMITER MODE

In limiter mode, the ALC will reduce peaks that go above the threshold level, but will not increase the

PGA gain beyond the starting level. The starting level is the PGA gain setting when the ALC is

enabled in limiter mode. If the ALC is started in limiter mode, this is the gain setting of the PGA at

start-up. If the ALC is switched into limiter mode after running in ALC mode, the starting gain will be

the gain at switchover. The diagram below shows an example of limiter mode.

Figure 18 ALC Limiter Mode Operation

ALC LIMITER MODE INITIALISATION SEQUENCE

In order to properly initialise the ALC function, the following sequence of register writes is required:

Set INPPGAVOLL to the required input PGA gain (R45[5:0]).

Set INPPGAVOLR to the required input PGA gain (R46[5:0]).

Enable analogue inputs (R44[2:0]) as required.

Disable input PGA – set INPPGAENR (R2[3] =0) and INPPGAENL (R2[2] =0).

Set ALCMAXGAIN (R32[5:3]) and ALCMINGAIN (R32[2:0]) to the required level for

operation.

Set ALCLVL (R33[3:0]) to the required level for operation.

Set R34 to 0x000.

Wait for 1ms to allow the input PGA gain to update by the limiter circuit.

Enable Limiter mode (R34[8]=1).

10. Wait for 1ms to allow the input PGA gain to update by the limiter circuit.

11. Enable input PGA – set INPPGAENR (R2[3] =1) and INPPGAENL (R2[2] =1).

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