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AS3542 3v2
Data Sheet, Strictly Confidential - D e ta 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 Register
Description
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.
Please not that only single ended mode is possible for the microphone input, make sure that the MIC_MODE in reg.
06h is set for enalbing the single ended mode.
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 7. Line Input Related Register
Name
Base
Offset
Description
2-wire serial
0Ah
Right Line Input settings
2-wire serial
0Bh
Left Line Input settings
2-wire serial
14h
Enable/disable driver stage
2-wire serial
16h
Enable/disable mixer input