LMP8278

+

-

Preamplifier

+IN

-IN

Output Buffer

Gain = 2

A1

A2

Gain = 7

Vs

Internal

Resistor

100 k:

OUT

Proprietary

Level Shift

Circuit

GND

LMP8278

www.ti.com

SNAS575A – FEBRUARY 2012 – REVISED MARCH 2013

APPLICATION INFORMATION

GENERAL

The LMP8278 is a fixed gain differential voltage precision amplifier with a gain of 14x and a -2V to +40V input

common mode voltage range when operating from a single 5V supply. The LMP8278 is a member of the LMP™

family and is ideal for unidirectional current sensing applications. Because of its proprietary level-shift input stage

the LMP8278 achieves very low offset, very low thermal offset drift, and very high CMRR. The LMP8278

amplifies and filters small differential signals in the presence of high common mode voltages.

The LMP8278 uses level shift resistors at the inputs. Because of these resistors, the LMP8278 can easily

withstand very large differential input voltages that may exist in fault conditions where some other less protected

current sense amplifiers might sustain permanent damage.

The LMP8278 is available in an 8–Pin VSSOP package. For the VSSOP package, the pitch of the solder pads is

coating on the PCB assembled with the LMP8278 in VSSOP package.

PERFORMANCE GUARANTIES

To guaranty the high performance of the LMP8278, minimum and maximum values shown in the Electrical

Characteristics of this datasheet are 100% tested and all bold limits are also 100% tested over temperature,

unless otherwise noted.

THEORY OF OPERATION

The schematic shown in Figure 20 gives a schematic representation of the internal operation of the LMP8278.

The signal on the input pins is typically a small differential voltage across a current sensing shunt resistor. The

input signal may appear at a high common mode voltage. The input signals are accessed through two input

resistors. The proprietary level shift circuit brings the common mode voltage behind the input resistors within the

supply rails. Subsequently, the signal is gained up by a factor of 7 and brought out on the A1 pin through a

trimmed 100 k

Ω resistor. In the application, additional gain adjustment or filtering components can be added

between the A1 and A2 pins as will be explained in subsequent sections. The signal on the A2 pin is further

amplified by a factor of 2 and brought out on the OUT pin.

Figure 20. Theory of Operation

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