+

-

+

-

R1

1 k:

LMV86x

Buffer

R11

1 k:

R2

1 k:

R12

995:

V

-

V

+

P1

10:

V

+

BUFFER

V

-

BUFFER

LMV861, LMV862

www.ti.com

SNOSAZ5A – FEBRUARY 2008 – REVISED JULY 2008

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.

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

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.

Copyright © 2008, Texas Instruments Incorporated

Submit Documentation Feedback

13

Product Folder Links: LMV861 LMV862