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
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 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 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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