AS3658F-BCTP datasheet(110/158 Pages) AMSCO

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AS3658

Data Sheet Confidential - Detail ed Descri ption- Audio Functi ons

9.10

Line Output

9.10.1 General

The line output is designed to provide the audio signal on 600

Ω min.

This output stage has an independent gain regulation for left and right channel with 32 steps @ 1.5dB each. The gain

can be set from –40.5dB to +6dB.

9.10.2 No-Pop Function

To avoiding click and pop noise during power-up and shutdown, the output is automatically set to mute when the output

stage is disabled. Also the volume settings are set to their default values, and can’t be changed, as long the output

stage is not enabled.

LINE_CM pin, which needs a 0.1µF... 1µF capacitor outside gets charged on power-up with 1µA to ALVDD/2. After

start-up the DC level of the following pins are the same: LOUT_L=LOUT_R=LINE_CM= ALVDD/2. The Start-up time

before releasing mute is about 150ms with 0.1µF. To avoid pop-noise 150ms discharging time of LINE_CM after a

shutdown, have to be waited before starting up again.

9.10.3 Ground Noise Cancellation

The purpose of the ground cancellation circuit is to compensate noise (ground noise) between different grounds (e.g.

the ground where the AS3658 is soldered versus e.g. the ground of a car amplifier (see Figure 50)). This noise

between these different grounds can be caused e.g. by a high current devices like a motor-fan. The ground

cancellation circuit can be used for line and headphone amplifiers.

The circuit works as follows:

The ground noise gets added inside the AS3658 to the audio signal (input LINE_CM for the Line Out amplifier or

HP_CM for headphone amplifier) in a way that it cancels inside the car amplifier. The sense point is connected with

RGND_SEP (20

Ω) to the battery ground.

agc_off

R/W

Switches the signal limiter OFF

automatic gain control for summing stage

enabled

automatic gain control for summing stage

disabled

dacmix_off

R/W

Input from DAC to R and L

0ON

1OFF

micmix_off

R/W

Input from microphone to R and L

0ON

1OFF

linmix_off

R/W

Input from line input to R and L

0ON

1OFF

Table 113. AudioSet_3 Register

Addr:76

Audio_set3 register

Configures the mixer inputs and AGC

Bit

Bit Name

Default

Access

Description

AS3658F-BCTP Datasheet(PDF) 110 Page - ams AG

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