AS3525-A/-B C22O22
Data Sheet, Confidential
7.4.8
Microphone Inputs (2x)
7.4.8.1 General
The chip features two identical microphone inputs. The blocks have differential inputs to a microphone amplifier with adjustable gain. This stage
also includes an AGC.
The following volume control 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. The stage is set to mute by default. If the microphone input is not enabled, the volume settings are set to their default values.
Changing of volume and mute control can only be done after enabling the input.
Figure 52 Microphone Input
Microphone Preamplifier and Gain Stage
7.4.8.2 AGC
The microphone amplifier includes an AGC, which is limiting the signal to 1Vp. The AGC has 15 steps with a dynamic range of about 29dB. The
AGC is ON by default but can be disabled by a microphone register bit.
7.4.8.3 Supply & Detection
Each microphone input generates a supply voltage of 1.5V above HPHCM. The supply is designed for ≤2mA and has a 10mA current limit. In OFF
mode the MICSUP terminal is pulled to AVDD with 30kohm. A current of typically 50uA generates an interrupt to inform the CPU, that a circuit is
connected. When using HPHCM as headset ground the HPH–stage gives the interrupt. After enabling the HPH-stage through the CPU the
microphone detection interrupt will follow.
7.4.8.4 Remote Control
Fast changes of the supply current of typically 500uA are detected as a remote button press, and an interrupt is generated. Then the CPU can start
the measurement of the microphone supply current with the internal 10-bit ADC to distinguish which button was pressed. As the current
measurement is done via an internal resistor, only two buttons generating a current of about 0.5mA and 1mA can be detected. With this 1mA as
microphone bias is still available.
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