Datasheet

V
IN
+
-
+
-
R1
1 k:
LMV86x
Buffer
V
OUT
R11
1 k:
R2
1 k:
R12
995:
V
-
V
+
P1
10:
V
+
BUFFER
V
-
BUFFER
LMV861, LMV862
www.ti.com SNOSAZ5C –FEBRUARY 2008–REVISED MARCH 2013
APPLICATION INFORMATION
INTRODUCTION
The LMV861 and LMV862 are operational amplifiers with excellent specifications, such as low offset, low noise
and a rail-to-rail output. These specifications make the LMV861 and LMV862 great choices for medical and
instrumentation applications such as diagnosis equipment and power line monitors. The low supply current is
perfect for battery powered equipment. The small packages, SC70 package for the LMV861, and the VSSOP
package for the dual LMV862, make these parts a perfect choice for portable electronics. Additionally, the EMI
hardening makes the LMV861 and LMV862 a must for almost all op amp applications. Most applications are
exposed to Radio Frequency (RF) signals such as the signals transmitted by mobile phones or wireless
computer peripherals. The LMV861 and LMV862 will effectively reduce disturbances caused by RF signals to a
level that will be hardly noticeable. This again reduces the need for additional filtering and shielding. Using this
EMI resistant series of op amps will thus reduce the number of components and space needed for applications
that are affected by EMI, and will help applications, not yet identified as possible EMI sensitive, to be more robust
for EMI.
INPUT CHARACTERISTICS
The input common mode voltage range of the LMV861 and LMV862 includes ground, and can even sense well
below ground. The CMRR level does not degrade for input levels up to 1.2V below the supply voltage. For a
supply voltage of 5V, the maximum voltage that should be applied to the input for best CMRR performance is
thus 3.8V.
When not configured as unity gain, this input limitation will usually not degrade the effective signal range. The
output is rail-to-rail and therefore will introduce no limitations to the signal range.
The typical offset is only 0.273 mV, and the TCV
OS
is 0.7 μV/°C, specifications close to precision op amps.
CMRR MEASUREMENT
The CMRR measurement results may need some clarification. This is because different setups are used to
measure the AC CMRR and the DC CMRR.
The DC CMRR is derived from ΔV
OS
versus ΔV
CM
. This value is stated in the tables, and is tested during
production testing. The AC CMRR is measured with the test circuit shown in Figure 44.
Figure 44. AC CMRR Measurement Setup
The configuration is largely the usually applied balanced configuration. With potentiometer P1, the balance can
be tuned to compensate for the DC offset in the DUT. The main difference is the addition of the buffer. This
buffer prevents the open-loop output impedance of the DUT from affecting the balance of the feedback network.
Now the closed-loop output impedance of the buffer is a part of the balance. But as the closed-loop output
impedance is much lower, and by careful selection of the buffer also has a larger bandwidth, the total effect is
that the CMRR of the DUT can be measured much more accurately. The differences are apparent in the larger
measured bandwidth of the AC CMRR.
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