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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

Figure 23. I2C Mode Start-Up Sequence

The total start-up time (including fade-in of the gain stages) can be reduced to 600ms by OTP setting.

9.5.3

MODE_CSCL Switching

When the chip is in stand-alone mode (no I2C control), the mode can be switched with different levels on the MODE pin.

In I2C mode, the monitor mode can be activated be setting the corresponding bit in the system register.

Table 10. MODE_CSCL Operation Modes

MODE

MODE_CSCL pin

Description

OFF

LOW (VSS)

Chip is turned off

ANC

HIGH (VBAT)

Chip is turned on and active noise cancellation is active

MONITOR

VBAT/2

Chip is turned on and monitor mode is active

In Monitor mode, a different (normally higher) microphone preamplifier gain can be chosen to get

an amplification of the surrounding noise. This volume can be either fixed or be controlled by the

VOL input.

To get rid of the low pass filtering needed for the noise cancellation, the headphone input

multiplexer can be set to a different (normally to MIC) source.

In addition, the LineIn gain can be lowered to reduce the loudness of the music currently played

back.

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