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AS3400 AS3410 AS3430 1v0

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

8.2 Microphone Input

The AFE offers two microphone inputs and one low noise microphone voltage supply (microphone bias). The inputs can be switched to single

ended or differential mode.

Figure 13. Microphone Input

8.2.1 Gain Stage & Limiter

The Mic GainStage has programmable Gain within -6dB…+41.625dB in 128 steps of 0.375dB.

As soft-start function is implemented for an automatic gain ramping implemented with steps of 4ms to fade in the audio at the end of the start-up

sequence.

A limiter automatically attenuates high input signals. The AGC has 127 steps with 0.375dB with a dynamic range of the full gain stage.

In monitor mode, the gain stage can be set to an fixed (normally higher) gain level or be controlled by the VOL pin.

8.2.2 Supply

The MICS charge pump is providing a proper microphone supply voltage for the AAA supply. Since AAA batteries are operating down to 1.0V,

the direct battery voltage cannot be used for mic-supply. There are 2 modes.

The first mode SWITCH-MODE for 1.8V supply is to have just a switch from VBAT to MICS. With this switch, the microphone current is switched

off in idle mode.

The second mode CHAREGPUMP_MODE for AAA batteries is the real charge pump mode, in this mode a positive voltage is generated of about

2* VBAT.

It is also possible to switch off the microphone supply if not needed (e.g. playback without ANC)

Gain Ramp Rate

PotiMode, Tinit=100ms

20

ms/step

ButtonMode, Tinit=400ms

80

MonitorMode

8

Limiter Activation Level

HPL/R start of neg. clipping

Limiter Release Level

HPL/R

VNEG

+0.3

Limiter Attack Time

4µs

Limiter Decay Time

8ms

Table 4. Line Input Parameter (Continued)

Symbol

Parameter

Condition

Min

Typ

Max

Unit

AGND

MICL

stereo mode

MICR

QMICR

QMICL

mono differential mode

AGND

MICL

MICR

QMICR

QMICL

AGND