Specifications

44
C3
C4
MIC_BIAS
MIC
MIC_A_P
MIC_A_N
R1
R2
C1
C2
2V7
regulator
EN
OUT
IN VDD_BAT
Figure 18: Recommended microphone biasing (left channel shown)
The input impedance at AUDIO_IN_N_LEFT, AUDIO_IN_P_LEFT, AUDIO_IN_N_RIGHT and
AUDIO_IN_P_RIGHT is typically 6.0kΩ. C1 and C2 should be 150nF if bass roll-off is
required to limit wind noise on the microphone. R1 sets the microphone load impedance
and is normally in a range of 1 to 2 kΩ. R2, C3 and C4 improve the supply rejection by
decoupling supply noise from the microphone. Values should be selected as required. R1
may be connected to a convenient supply, in which case the bias network is permanently
enabled, or to the output of the biasing regulator which may be configured to provide bias
only when the microphone is required.
The microphone bias provides a 4-bit programmable output voltage with a 4-bit
programmable output current, shown in Table 16 and 17.
Output Step Typical Voltage Level (V)
0 1.71
1 1.76
2 1.82
3 1.87
4 1.95
5 2.02
6 2.10
7 2.18
8 2.32
9 2.43
10 2.56
11 2.69
12 2.9