LMV922M National Semiconductor, LMV922M Datasheet - Page 19

• Manufacturer Part Number: LMV922M
• Description: IC OP AMP R-R I/O LP 8-SOIC
• Manufacturer: National Semiconductor

Specifications of LMV922M

• Amplifier Type: General Purpose
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Slew Rate: 0.45 V/µs
• Gain Bandwidth Product: 1MHz
• Current - Input Bias: 12nA
• Voltage - Input Offset: 1500µV
• Current - Supply: 400µA
• Current - Output / Channel: 75mA
• Voltage - Supply, Single/dual (±): 1.5 V ~ 5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• -3db Bandwidth: -
• Other names: *LMV922M

Typical Applications
2.0 Instrumentation Amplifier with Rail-To-Rail Input and
Output
Using three of the LMV924 Amplifiers, an instrumentation
amplifier with rail-to-rail inputs and outputs can be made.
Some manufacturers use a precision voltage divider array of
5 resistors to divide the common mode voltage to get a
rail-to-rail input range. The problem with this method is that it
also divides the signal, so in order to get unity gain, the
amplifier must be run at high loop gains. This raises the
noise and drift by the internal gain factor and lowers the input
impedance. Any mismatch in these precision resistors re-
duces the CMRR as well. Using the LMV924 eliminates all of
these problems.
In this example, amplifiers A and B act as buffers to the
differential stage. These buffers assure that the input imped-
Simplified Schematic
(Continued)
FIGURE 7. Rail-to-rail instrumentation amplifier
19
ance is very high and require no precision matched resistors
in the input stage. They also assure that the difference amp
is driven from a voltage source. This is necessary to main-
tain the CMRR set by the matching R
The gain is set by the ratio of R
and R
With both rail-to-rail input and output ranges, the input and
output are only limited by the supply voltages. Remember
that even with rail-to-rail outputs, the output can not swing
past the supplies so the combined common mode voltages
plus the signal should not be greater that the supplies or
limiting will occur. For additional applications, see National
Semiconductor application notes AN–29, AN–31, AN–71,
and AN–127.
4
equal R
2
.
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2
/R
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1
and R
1
-R
2
3
with R
should equal R
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3
-R
4
.
1