Datasheet

A_V
DD
LS_V
DD
LEFT_MIC+
MIC_BIAS
RIGHT_MIC+
RIGHT_MIC-
LEFT_MIC-
V
DD
R
B
C
B
A_V
DD
LS_V
DD
LEFT_MIC+
MIC_BIAS
RIGHT_MIC+
RIGHT_MIC-
LEFT_MIC-
V
DD
LS_V
DD
LEFT_MIC+
MIC_BIAS
RIGHT_MIC+
RIGHT_MIC-
LEFT_MIC-
V
DD
R
B
C
B
LM49350, LM49350RLEVAL
www.ti.com SNAS359D –SEPTEMBER 2008–REVISED JUNE 2012
MICROPHONE BIAS CONFIGURATIONS
Schematic Considerations for MEMs Microphones
The internal microphone bias of the LM49350 is provided through a two stage amplifier. Adding a capacitor larger
than 100pF directly to this pin can cause instability. In many cases, when using MEMs microphones, a larger
bypass capacitor is required on the MIC_BIAS pin. To avoid oscillations and to keep the device stable, it is
recommended to add a resistor (R
B
) greater than 10Ω in series with the capacitor (C
B
). Another option is to bias
the MEMs microphone from the 1.8V supply used for D_V
DD
/IO_V
DD
.
Figure 74. Schematic for MEMs Microphones
Schematic Considerations for ECM Microphones
When using ECM microphones, refer to the configurations shown in Figure 73 or Figure 74 to bias the
microphones. In many cases, an RC filter is required to provide a more stable microphone bias (see Figure 74).
In this case, a 10Ω resistor (R
B
) in series with C
B
is recommended.
Figure 75. Schematic Option for ECM Microphones Figure 76. Schematic Option for ECM Microphones
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