Texas Instruments LM49370RLEVAL Evaluation Board LM49370RLEVAL/NOPB LM49370RLEVAL/NOPB 데이터 시트
제품 코드
LM49370RLEVAL/NOPB
LS_V
DD
EXT_MIC_BIAS
INT_MIC_BIAS
INT_MIC_POS
INT_MIC_NEG
V
DD
MIC_DET
EXT_MIC
A_V
DD
LS_V
DD
EXT_MIC_BIAS
INT_MIC_BIAS
INT_MIC_POS
INT_MIC_NEG
V
DD
R
B
C
B
MIC_DET
EXT_MIC
A_V
DD
SNAS356D – FEBRUARY 2007 – REVISED MARCH 2012
APPLICATION NOTE
MICROPHONE BIAS CONFIGURATIONS
Schematic Considerations for MEMs Microphones
The internal microphone bias of the LM49370 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 INT_MIC_BIAS pin. To avoid oscillations and to keep the device stable, it is
recommended to add a resistor (R
than 100pF directly to this pin can cause instability. In many cases, when using MEMs microphones, a larger
bypass capacitor is required on the INT_MIC_BIAS pin. To avoid oscillations and to keep the device stable, it is
recommended to add a resistor (R
B
) greater than 10
Ω
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 218. Schematic for MEMs Microphones
Schematic Considerations for ECM Microphones
When using ECM microphones, refer to the configurations shown in
to bias the microphones.
Figure 219. Schematic Option for ECM Microphones
PCB LAYOUT CONSIDERATIONS
A_V
DD
and LS_V
DD
Due to internal ESD diodes structure, for best performance, in the PCB board A_V
DD
and LS_V
DD
need to be tied
to the same plane, but requires separate bypassing capacitors for each supply rail.
Microphone Inputs
When routing the differential microphone inputs the electrical length of the two traces should be well matched.
The differential input pair can be routed in parallel on the same plane or the traces can overlap on two adjacent
planes. It is important to surround these traces with a ground plane or trace to isolate the microphone inputs from
the noise coupling from the class D amplifier.
The differential input pair can be routed in parallel on the same plane or the traces can overlap on two adjacent
planes. It is important to surround these traces with a ground plane or trace to isolate the microphone inputs from
the noise coupling from the class D amplifier.
Copyright © 2007–2012, Texas Instruments Incorporated
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