LMP8278

+

-

Preamplifier

Output Buffer

Gain = 2

A1

A2

Gain = 7

Internal

Resistor

100 k:

C1

POWER

SWITCH

INDUCTIVE

LOAD

+IN

-IN

OUT

0.01

Ö

1

5

3

4

8

24V

LMP8278

www.ti.com

SNAS575A – FEBRUARY 2012 – REVISED MARCH 2013

LOW SIDE CURRENT SENSING APPLICATION

Figure 27 illustrates a low side current sensing application with a low side driver. The power transistor is pulse

width modulated to control the average current flowing through the inductive load which is connected to a

with the load. When the power transistor is on, current flows from the battery through the inductive load, the

shunt resistor and the power transistor to ground. In this case, the common mode voltage on the shunt is close

to ground. When the power transistor is off, current flows through the inductive load, through the shunt resistor

and through the freewheeling diode. In this case the common mode voltage on the shunt is at least one diode

voltage drop above the battery voltage. Therefore, in this application the common mode voltage on the shunt is

varying between a large positive voltage and a relatively low voltage. Because the large common mode voltage

range of the LMP8278 and because of the high AC common mode rejection ratio, the LMP8278 is very well

suited for this application.

Figure 27. Low Side Current Sensing Application

HIGH SIDE CURRENT SENSING APPLICATION

Figure 28 illustrates the application of the LMP8278 in a high side sensing application. This application is similar

to the low side sensing discussed above, except in this application the common mode voltage on the shunt drops

below ground when the driver is switched off. Because the common mode voltage range of the LMP8278

extends below the negative rail, the LMP8278 is also very well suited for this application.

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