LMP8602MM datasheet(14/24 Pages) NSC

14 / 24 page

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/LMP8602Q/LMP8603/LMP8603Q use level

shift resistors at the inputs. Because of these resistors, the

LMP8602/LMP8602Q/LMP8603/LMP8603Q can easily with-

stand very large differential input voltages that may exist in

fault conditions where some other less protected high-perfor-

mance current sense amplifiers might sustain permanent

damage.

PERFORMANCE GUARANTIES

To guaranty the high performance of the LMP8602/LM-

P8602Q/LMP8603/LMP8603Q, 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 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 k

Ω 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.

30083405

K2 = 5 for LMP8602, K2 = 10 for LMP8603

FIGURE 1. Theory of Operation

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