Production Data
WM8978
w
PD, Rev 4.5, October 2011
39
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:
1.
Set INPPGAVOLL to the required input PGA gain (R45[5:0]).
2.
Set INPPGAVOLR to the required input PGA gain (R46[5:0]).
3.
Enable analogue inputs (R44[2:0]) as required.
4.
Disable input PGA – set INPPGAENR (R2[3] =0) and INPPGAENL (R2[2] =0).
5. Set ALCMAXGAIN (R32[5:3]) and ALCMINGAIN (R32[2:0]) to the required level for
operation.
6.
Set ALCLVL (R33[3:0]) to the required level for operation.
7.
Set R34 to 0x000.
8.
Wait for 1ms to allow the input PGA gain to update by the limiter circuit.
9.
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).
Summary of Contents for WM8978
Page 11: ...Production Data WM8978 w PD Rev 4 5 October 2011 11 SPEAKER OUTPUT THD VERSUS POWER...
Page 14: ...WM8978 Production Data w PD Rev 4 5 October 2011 14 AUDIO PATHS OVERVIEW...
Page 55: ...Production Data WM8978 w PD Rev 4 5 October 2011 55 Figure 26 Left Right Output Channel Mixers...
Page 60: ...WM8978 Production Data w PD Rev 4 5 October 2011 60 Figure 29 Speaker Outputs LOUT2 and ROUT2...