AD8218

Rev. A | Page 12 of 16

APPLICATIONS INFORMATION

UNIDIRECTIONAL HIGH-SIDE CURRENT SENSING

In the unidirectional high-side current sensing configuration,

the shunt resistor is referenced to the battery (see Figure 31).

High voltage is present at the inputs of the current sense amplifier.

When the shunt is battery referenced, the AD8218 produces a

AD8218 can either be connected to a 5 V supply or left floating (see

the Supply (VS) Connections section).

LOAD

SHUNT

BATTERY

(4V TO 80V)

LDO

R2

R1

AD8218

R4

R3

+IN

–IN

OUT

ENB

REF

GND

Figure 31. Unidirectional Operation with ENB Connected to GND

The output transfer function curve for unidirectional operation

with ENB connected to GND is shown in Figure 32.

0

40

80

120

160

200

240

280

320

0

1

2

3

4

5

6

7

8

9

10

INPUT VOLTAGE (mV)

Figure 32. Output Transfer Function with ENB Connected to GND

BIDIRECTIONAL HIGH-SIDE CURRENT SENSING

Inputting a voltage at Pin 7 (REF) offsets the output of the AD8218

and allows for bidirectional current sensing. The transfer function

from the REF pin to the output is 1 V/V. For example, a 2.5 V REF

input offsets the output of the AD8218 to 2.5 V. See Figure 33

for typical connections. The user must ensure that the voltage

applied at Pin 7 (REF) is from a low impedance source.

SHUNT

LDO

R2

R1

AD8218

R4

R3

+IN

–IN

OUT

ENB

REF

2.5V

GND

LOAD

BATTERY

(4V TO 80V)

Figure 33. Bidirectional Operation Using a 2.5 V Reference Input

The output transfer function curve for bidirectional operation

using a 2.5 V reference input is shown in Figure 34.

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

–0.15

–0.10

–0.05

0

0.05

0.10

0.15

INPUT VOLTAGE (V)

Figure 34. Transfer Function When Using a 2.5 V Reference Input

MOTOR CONTROL CURRENT SENSING

The AD8218 is a practical, accurate solution for high-side

current sensing in motor control applications. In cases where

the shunt resistor is referenced to a battery and the current

flowing is bidirectional (as shown in Figure 35), the AD8218

monitors the current with no additional supply pin necessary.

GND

BATTERY

MOTOR

AD8218

+IN

–IN

REF

OUT

ENB

Figure 35. High-Side Current Sensing in Motor Control