LMV1089RLEVAL National Semiconductor, LMV1089RLEVAL Datasheet - Page 16

• Manufacturer Part Number: LMV1089RLEVAL
• Description: BOARD EVALUATION LMV1089
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LMV1089RLEVAL

• Main Purpose: Audio, Microphone Amp
• Embedded: No
• Utilized Ic / Part: LMV1089
• Primary Attributes: Dual Input, Single Output
• Secondary Attributes: Graphical User Interface, I²C Interface
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Automatic Calibration Setup
A calibration test setup consists of a test room (acoustical
box) with a loudspeaker (acoustical source) driven with the
test tone (e.g. the sequence from Creating the Three Tone
Sequence with an AWG). The test setup is shown in Figure
20. The distances between the source and microphone 1 and
microphone 2 must be equal and the sound must travel with-
out any obstacle from source to both microphones. The sound
Performing a Manual Calibration
The LMV1089 provides the option to program the calibration
parameters directly into the LMV1089 registers via the I
terface, instead of performing the above described Automatic
Calibration on each apparatus. This is very convenient for
applications where the microphones have good matching and
where the compensation for acoustical effect on the frequen-
cy and gain of the application are known. This manual cali-
bration is performed by writing the appropriate data to the
calibration registers of the LMV1089 as described in the ap-
plication section of the LMV1089 data sheet. This can be
much more time efficient in an application production envi-
ronment.
PCB Layout Guidelines
This section provides general practical guidelines for PCB
layouts that use various power and ground traces. Designers
FIGURE 20. Automatic Calibration Setup
2
C in-
16
will travel with the limited speed of 300m/s from the loud-
speaker source to the microphones. When creating the cali-
bration signals this time should not be ignored, 30cm distance
will cause 1ms delay.
For an optimum automatic calibration the output level of the
microphones and Pre-Amp gain must be set so that the re-
sulting signal at the output of the Pre-Amp is 100mV
should note that these are only "rule-of-thumb" recommen-
dations and the actual results are predicated on the final
layout.
Differential Signals
Keep both signals coupled by routing them closely together
and keeping them of equal length. Keep all impedances in
both traces of the signal equal.
Power and Ground
Connect all ground pins together under the part forming a star
point. Keep the current for the de-coupling capacitor of the
REF pin (D6) and the accompanying ground pin (C5) sepa-
rated from the other currents. Keep the location of the supply
de-coupling capacitor close to V
Avoid that the current for the de-coupling capacitors flow
though the ground from pin B4.
DD
pin (F3) and ground (D3).
300606r5
pp
± 6dB.