AS3543 datasheet(18/92 Pages) AMSCO

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AS3543 3v2

Data Sheet - D e t a i l e d D e s c r i p t i o n - A u d i o F u n c t i o n s

8.1.3

Line input has to be enabled in register 14h first before other settings in register 0Ah and 0Bh can be programmed.

8.2

Microphone Input

8.2.1

General

The AFE offers one microphone input and one low noise microphone voltage supply (microphone bias), voice activa-

tion, microphone connect detection and push button remote control.

Figure 4. Microphone Input

8.2.2

Gain Stage & Limiter

The integrated pre-amplifier allows 3 preset gain settings. There is also a limiter which attenuates high input signals

from e.g. electret microphones signal to 1Vp. The AGC has 128 steps with 0.375dB with a dynamic range of the full

pre-amplifier level. The AGC is ON by default but can be disabled by a microphone register bit.

Apart from the microphone pre-amplifier the microphone input signal can further be amplified with 32 @1.5dB pro-

grammable logarithmic gain steps and MUTE. All gains and MUTE are independently programmable. The gain can be

set from –40.5dB to +6dB.

The stage features a soft-start function. Pre-amplifier and gain-stage settings can be set before enabling the micro-

phone stage. After enabling the stage to gain is automatically set to the defined value by using the 128 steps of the

AGC.

8.2.3

Supply & Detection

Each microphone input generates a supply voltage of 1.5V above HPCM. The supply is designed for

≤2mA and has a

6.5mA current limit. In OFF mode the MICS terminal is pulled to AVDD with 20kOhm. A current of typically 50uA gen-

erates an interrupt to inform the CPU, that a circuit is connected. When using HPCM as headset ground the HP–stage

gives the interrupt. After enabling the HP-stage through the CPU the microphone detection interrupt will follow.

When using the MICS terminal as ADC-10 input to monitor external voltages the 20kOhm pull-up has to be disabled by

disabling the interrupt for microphone detection.

Table 8. Line Input Related Register

Name

Base

Offset

Description

LINE_IN_R

2-wire serial

0Ah

Right Line Input 1/2 settings, Line Input 2 selection

LINE_IN_L

2-wire serial

0Bh

Left Line Input 1/2 settings

AudioSet1

2-wire serial

14h

Enable/disable driver stage

AudioSet3

2-wire serial

16h

Enable/disable mixer input

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