User's Manual

41
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
13
3.08
14
3.33
15
3.57
Table 16: Voltage Output Step
Output Step
Typical Current (mA)
0
0.199
1
0.284
2
0.336
3
0.419
4
0.478
5
0.529
6
0.613
7
0.672
8
0.754
9
0.809
10
0.862
11
0.948
12
1.004
13
1.091
14
1.142
15
1.229
Table 17: Current Output Step