WM9090ECSSLASHR datasheet(29/81 Pages) WOLFSON

29 / 81 page

Production Data

WM9090

PD, November 2010, Rev 4.1

AGC POWER LIMITING

The second mechanism used by the AGC to monitor signal conditions is the power limit function.

The speaker output voltage is measured, and the corresponding power output is determined. The

power limiting function can be disabled using the AGC_PWR_ENA bit. It is enabled by default.

The power output threshold at which the AGC will apply attenuation is set using the AGC_PWR_THR

power levels, assuming an 8

Ω speaker.

The power output threshold is also controlled by the AGC_PWR_AVG register. When

AGC_PWR_AVG = 1, then the AGC responds to the RMS power level as quoted above. When

AGC_PWR_AVG = 0, then the AGC responds to the instantaneous voltage at the speaker output.

Selecting the RMS power level is recommended, as this represents the average signal level.

When the AGC applies signal attenuation triggered by the power limit threshold, the signal gain is

reduced at a rate that is set by the AGC_PWR_ATK register. When the power limit threshold is no

longer met (due to the signal level reduction), then the AGC increases the signal gain at a rate set by

the AGC_PWR_DCY register.

Note that, when the anti-clip and power limiting thresholds are both triggered concurrently, then the

signal gain is reduced at the rate set by the AGC_CLIP_ATK register and is increased at the rate set

by AGC_PWR_DCY. These fields are defined in Table 13 and Table 14 respectively.

WM9090ECS/R Scheda tecnica(PDF) 29 Page - Wolfson Microelectronics plc