Datasheet

Level shift
+
-
Preamplifier
Gain = 10
+IN
-IN
Output Buffer
Gain = K2
A1 A2
OFFSET
100 k:
OUT
V
S
GND
8
1
3 4
5
7
2
6
LMP8602, LMP8602Q, LMP8603, LMP8603Q
SNOSB36D –JULY 2009–REVISED MARCH 2013 www.ti.com
APPLICATION INFORMATION
GENERAL
The LMP8602 and LMP8603 are fixed gain differential voltage precision amplifiers with a gain of 50x for the
LMP8602, and 100x for the LMP8603. The input common mode voltage range is -22V to +60V when operating
from a single 5V supply or -4V to +27V input common mode voltage range when operating from a single 3.3V
supply. The LMP8602 and LMP8603 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
LMP8602 and LMP8603 achieve very low offset, very low thermal offset drift, and very high CMRR. The
LMP8602 and LMP8603 will amplify and filter small differential signals in the presence of high common mode
voltages.
The LMP8602/LMP8602Q/LMP8603/LMP8603Q use level shift resistors at the inputs. Because of these
resistors, the LMP8602/LMP8602Q/LMP8603/LMP8603Q 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 LMP8602/LMP8602Q/LMP8603/LMP8603Q, all minimum and maximum
values shown in the parameter tables of this datasheet are 100% tested where all bold limits are also 100%
tested over temperature.
THEORY OF OPERATION
The schematic shown in Figure 42 gives a schematic representation of the internal operation of the
LMP8602/LMP8603.
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 (K1) and brought out on the A1 pin through a trimmed 100 kΩ 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 (K2) which equals a
factor of 5 for the LMP8602 and a factor of 10 for the LMP8603. The output signal of the final gain stage is
provided 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 = 5 for LMP8602, K2 = 10 for LMP8603
Figure 42. Theory of Operation
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