Level shift

+

-

Preamplifier

Gain = 10

+IN

-IN

Output Buffer

Gain = K2

A1 A2

OFFSET

100 k:

OUT

GND

8

1

3

4

5

7

2

6

LMP8601, LMP8601-Q1

www.ti.com

SNOSAR2E – SEPTEMBER 2008 – REVISED MARCH 2013

APPLICATION INFORMATION

GENERAL

The LMP8601 and LMP8601Q are fixed gain differential voltage precision amplifiers with a gain of 20x and a -

22V to +60V input common mode voltage range when operating from a single 5V supply or a -4V to +27V input

common mode voltage range when operating from a single 3.3V supply. The LMP8601 and LMP8601Q are

members of the LMP family and are ideal parts for unidirectional and bidirectional current sensing applications.

Because of the proprietary chopping level-shift input stage the LMP8601/LMP8601Q achieve very low offset,

very low thermal offset drift, and very high CMRR. The LMP8601 and LMP8601Q will amplify and filter small

differential signals in the presence of high common mode voltages.

The LMP8601/LMP8601Q use level shift resistors at the inputs. Because of these resistors, the

LMP8601/LMP8601Q can easily withstand very large differential input voltages that may exist in fault conditions

where some other less protected high-performance current sense amplifiers might sustain permanent damage.

PERFORMANCE GUARANTIES

To guaranty the high performance of the LMP8601/ LMP8601Q, all minimum and maximum values shown in the

parameter tables of this data sheet are 100% tested where all bold limits are also 100% tested over temperature.

THEORY OF OPERATION

The schematic shown in Figure 33 gives a schematic representation of the internal operation of the

LMP8601/LMP8601Q.

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 chopping level-shift current circuit pulls or pushes current through the input resistors to

bring the common mode voltage behind these resistors within the supply rails. Subsequently, the signal is gained

up by a factor of 10 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. The OFFSET pin allows the output signal to be level-shifted to enable bidirectional current

sensing as will be explained below.

K2 = 2

Figure 33. Theory of Operation

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