LMP8275 Datasheet, PDF (10/15 Pages) Texas Instruments – Precision Voltage Difference Amplifier

LMP8275
OBSOLETE
SNOSAO3G – JUNE 2005 – REVISED APRIL 2013
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Assuming ideal behavior, the equation for K reduces simply to the DC gain, which is set for +2 for the LMP8270.
Using Equation 3, the filter parameters can be calculated as follows:
1
Z_{o =}
R₁R₂C₁C₂
1
f_c =
2S R1R2C1C2
Q=
R₁R₂C₁C₂
R₁C₁+R₂C₁+(1-K)R₁C₂
(4)
for the LMP8275, R₁ = 100 kΩ. Setting R₁ = R₂ and C₁ = C₂ results in a low pass filter with Q = 1. Since the
values of resistors are predetermined, the corner frequency of this implementation of the filter depends on the
capacitor values.
GAINS OTHER THAN 20
THe LMP8275 has an internal gain of +20; however this gain can be modified. The signal path between the two
amplifiers is available as external pins.
GAINS LESS THAN 20
Figure 23 shows the configuration used to reduce the LMP8275 gain.
V_S = 4.75V to 5.5V
LMP8275
+IN
PROPRIETARY
+
A1
-IN
LEVEL - SHIFT
CIRCUITRY
GAIN = 10
-
100 k:
A2
GAIN = 2
OUT
GND
R_G A1 A2
Figure 23. Gains Less Than 20
Where:
20 R_G
GAIN (NEW) =
R_G + 100 k:
(5)
and
GAIN (NEW)
R_G = (100 k:) _{20 - GAIN (NEW)}
(6)
10
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