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AS3421 AS3422

Datasheet - D e t a i l e d D e s c r i p t i o n

9 Detailed Description

This section provides a detailed description of the device related components.

9.1 Audio Line Input

The chip features one line input. The blocks can work in mono differential or in stereo single ended mode.

In addition to the 12.5-25k

Ω input impedance, LineIn has a termination resistor of 10kΩ which is also effective during MUTE to charge

eventually given input capacitors.

9.1.1

Gain Stage

The Line In gain stage is designed to have 63 gain steps of 0.75dB with a max gain of 0dB plus MUTE per default. By setting the bit Line Gain

+3dB in register 0x33 the gain range can be changed from -46.5dB....0dB to -43.5dB ....+3dB.

In default, the gain will be ramped up from MUTE to 0dB during startup. There is a possibility to make the playback volume user controlled by the

VOL pin with an ADC converted VOL voltage or UP/DOWN buttons. If the device is configured to control the line input volume via push-buttons

the device ramps the gain from -46.5dB to 0dB if no button is pressed. If a user presses a button while ramping up the ramping mechanism will

be stopped automatically.

In monitor mode, the gain stage can be set to an fixed default attenuation level for reducing the loudness of the music. To avoid unwanted pop

noise in this special mode the internal state machine support very smooth gain fading to avoid unwanted acoustic effects.

Figure 17. Fully Differential Stereo Line Inputs

9.1.2

Parameter

Table 4. Line Input Parameter

Symbol

Parameter

Condition

Min

Typ

Max

Unit

Input Signal Level

0.6*

VBAT

VBAT

Input Impedance

0dB gain (12.5k // 10k)

5.6

k

-46.5dB gain (25k // 10k)

7.2

k

MUTE

10

k

Input Impedance Tolerance

±30

%

Input Capacitance

5

pF

Programmable Gain

-46.5

+0

dB

Gain Steps

Discrete logarithmic gain steps

0.75

dB

Gain Step Accuracy

0.5

dB

Mute Attenuation

100

dB