LMP8602MA NSC [National Semiconductor], LMP8602MA Datasheet - Page 14

• Manufacturer Part Number: LMP8602MA
• Description: 60V Common Mode, Fixed Gain, Bidirectional Precision Current Sensing Amplifier
• Manufacturer: NSC [National Semiconductor]

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Application Information
GENERAL
The LMP8602 and LMP8603 are fixed gain differential volt-
age 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 op-
erating 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 applica-
tions. 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 differen-
tial signals in the presence of high common mode voltages.
The LMP8602/LMP8603 use level shift resistors at the inputs.
Because of these resistors, the LMP8602/LMP8603 can eas-
ily withstand very large differential input voltages that may
exist in fault conditions where some other less protected high-
performance current sense amplifiers might sustain perma-
nent damage.
PERFORMANCE GUARANTIES
To guaranty the high performance of the LMP8602/LMP8603,
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.
FIGURE 1. Theory of Operation
K2 = 5 for LMP8602, K2 = 10 for LMP8603
14
THEORY OF OPERATION
The schematic shown in Figure 1 gives a schematic repre-
sentation 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 propri-
etary chopping level-shift current circuit pulls or pushes cur-
rent through the input resistors to bring the common mode
voltage behind these resistors within the supply rails. Subse-
quently, 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 com-
ponents 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 be-
low.
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