Data Sheet

FSC-BT806BDatasheet
Shenzhen Feasycom Technology Co.,Ltdwww.feasycom.com
-27-
Microphone Input
FSC-BT806B contains an independent low-noise microphone bias generator. The microphone bias generator is
recommended for biasing electret condensor microphones. Figure 9.6 shows a biasing circuit for microphoneswith a
sensitivity between about -40 to -60dB (0dB = 1V/Pa).
Where:
The microphone bias generator derives its power from VBAT or 3V3_USB and requires no capacitor
on its output.
The microphone bias generator maintains regulation within the limits 70uA to 2.8mA, supporting a
2mAsource typically required by 2 electret condensor microphones. If the microphone sits below
these limits,then the microphone output must be pre-loaded with a large value resistor to ground.
Biasing resistors R1 and R2 equal 2.2kΩ.
When the input pre-amplifier is enabled, the input impedance at MIC_LN, MIC_LP, MIC_RN and
MIC_RPvaries between 6kΩ(pre-amplifier gain >0dB) and 12kΩ(pre-amplifier gain = 0dB).
C1, C2, C3 and C4 are 100/150nF if bass roll-off is required to limit wind noise on the microphone.
R1 and R2 set the microphone load impedance and are normally around 2.2kΩ.
Figure 14: Microphone Biasing
The microphone bias characteristics include:
Power supply:
FSC-BT806B microphone supply is VBAT or 3V3_USB(inernal)
Minimum input voltage = Output voltage + drop-out voltage
Maximum input voltage is 4.3V
Drop-out voltage:
300mV maximum
Output voltage: