AD8218 Data Sheet
Rev. B | 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 32).
High voltage is present at the inputs of the current sense amplifier.
When the shunt is battery referenced, the AD8218 produces a
linear ground-referenced analog output. The supply pin, V
S
, of the
AD8218 can either be connected to a 5 V supply or left floating (see
the Supply (V
S
) Connections section).
LOAD
V
2
I
LOAD
V
1
SHUNT
BATTERY
(4V TO 80V)
LDO
R2
R1
AD8218
R4
R3
+IN
–IN
OUT
ENB
REF
GND
V
S
09592-031
Figure 32. Unidirectional Operation with ENB Connected to GND
The output transfer function curve for unidirectional operation
with ENB connected to GND is shown in Figure 33.
0
40
80
120
160
200
240
280
320
0 1 2 3 4 5 6 7 8 9 10
INPUT VOLT
AGE (mV)
OUTPUT VOLTAGE (mV)
09592-032
Figure 33. 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 34
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
V
S
09592-033
LOAD
V
2
I
LOAD
V
1
BATTERY
(4V TO 80V)
Figure 34. 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 35.
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)
OUTPUT VOLTAGE (V)
09592-034
Figure 35. 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 36), the AD8218
monitors the current with no additional supply pin necessary.
GND
BATTERY
MOTOR
I
MOTOR
AD8218
+IN
V
S
V
REF
–IN
REF
OUT
ENB
09592-035
Figure 36. High-Side Current Sensing in Motor Control
