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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via the I
gain.
The default gain is only set during power up of the device.
Toggling the logic level of the enable pin (EN) will not change
the current gain setting of the part. Any gain setting done via
the I
tion.
Gain Balance and Gain Budget
In systems where input signals have a high dynamic range,
critical noise levels or where the dynamic range of the output
voltage is also limited, careful gain balancing is essential for
the best performance. Too low of a gain setting in the pream-
plifier can result in higher noise levels while too high of a gain
Example 1
An application using microphones with 50mV
output voltage, and a baseband chip after the LMV1089 with
1.5V
For optimum noise performance, the gain of the input stage
should be set to the maximum.
1.
2.
3.
4.
2
GA1
50mV
3.1V
the Noise Cancelling Processor (NCP). This means a
gain lower than 28.9dB should be selected.
Select the nearest lower gain from the gain settings
shown in Table 2, 28dB is selected. This will prevent the
NCP from being overloaded by the microphone. With this
setting, the resulting output level of the Pre Amplifier will
be 1.26V
The NCP can have a maximum processing gain of 9dB
(depending on the calibration result) which will result in
P-P
C interface will remain valid during activation of the func-
0
0
1
1
maximum input voltage.
2
P-P
C interface (see
P-P
TABLE 2. Default preamplifier gain
is higher than the maximum 1.4V
P-P
+36 dB = 3.1V
.
GA0
0
1
0
1
Table
P-P
.
6) will override this default
20dB
12dB
28dB
36dB
Gain
(Note
FIGURE 5. Maximum Signal Levels
P-P
P-P
9)
allowed for
maximum
16
Note 9: Default value used for performance measurements
setting in the preamplifier will result in clipping and saturation
in the noise cancelling processor and output stages.
The gain ranges and maximum signal levels for the different
functional blocks are shown in
given as a guideline on how to select proper gain settings.
5.
6.
7.
So using preamp gain = 14dB and postamp gain = 6dB is the
optimum for this application.
GB1
3.5V
then maximum level that is allowed at the input of the post
amp of the LMV1089. Therefore the preamp gain has to
be reduced, to 1.4V
the preamp gain to a maximum of 20dB.
The baseband chip limits the maximum output voltage to
1.5V
results in requiring a lower level at the input of the post
amp of 0.75V
NCP gain of 9dB the output of the preamp must be
<266mV
Calculating the new gain for the preamp will result in
<1.4dB gain.
The nearest lower gain will be 14dB.
0
0
1
1
P-P
P-P
TABLE 3. Default post amplifier gain
at the output of the LMV1089. This level is higher
with the minimum of 6dB post amp gain, this
P-P
.
P-P
GB0
0
1
0
1
. Now calculating this for a maximum
P-P
minus 9dB = 0.5V
Figure
6dB
5. Two examples are
30047241
12dB
15dB
Gain
9dB
(Note
P-P
9)
. This limits