Data Sheet AD8216
Rev. C | Page 13 of 16
APPLICATIONS INFORMATION
A typical application for the AD8216 is high-side measurement
of a current through a solenoid for PWM control of the solenoid
opening. Typical applications include dc-to-dc converters,
motor controls, and solenoid controls.
Two typical circuit configurations are used for this type of
application.
HIGH-SIDE CURRENT SENSE WITH A LOW-SIDE
SWITCH
In this case, the PWM control switch is ground referenced. An
inductive load (solenoid) is tied to a power supply. A resistive
shunt is placed between the switch and the load (see Figure 29).
An advantage of placing the shunt on the high side is that the
entire current, including the recirculation current, can be
measured because the shunt remains in the loop when the
switch is off. In addition, diagnostics can be enhanced because
shorts to ground can be detected with the shunt on the high side.
In this circuit configuration, when the switch is closed, the
common-mode voltage moves down to near the negative rail.
When the switch is opened, the voltage reversal across the
inductive load causes the common-mode voltage to be held
one diode drop above the battery by the clamp diode.
+IN V
REF
1 V+ OUT
–IN GND V
REF
2 NC
INDUCTIVE
LOAD
AD8216
CLAMP
DIODE
42V
BATTERY
SHUNT
SWITCH
NC = NO CONNECT
5V
07062-034
Figure 29. Low-Side Switch
HIGH-SIDE CURRENT SENSE WITH A HIGH-SIDE
SWITCH
This configuration minimizes the possibility of unexpected
solenoid activation and excessive corrosion (see Figure 30). In
this case, both the switch and the shunt are on the high side.
When the switch is off, it removes the battery from the load,
which prevents damage from potential shorts to ground, while still
allowing the recirculating current to be measured and providing
for diagnostics. Removing the power supply from the load for
the majority of the time minimizes the corrosive effects that
could be caused by the differential voltage between the load
and ground.
When using a high-side switch, the battery voltage is connected
to the load when the switch is closed, causing the common-
mode voltage to increase to the battery voltage. In this case,
when the switch is opened, the voltage reversal across the
inductive load causes the common-mode voltage to be held
one diode drop below ground by the clamp diode.
+IN
V
REF
1 V+
OUT
–IN
GND
V
REF
2 NC
INDUCTIVE
LOAD
AD8216
CLAMP
DIODE
42V
BATTERY
SHUNT
SWITCH
NC = NO CONNECT
5V
07062-035
Figure 30. High-Side Switch
Another typical application for the AD8216 is as part of the
control loop in H-bridge motor controls. In this case, the AD8216
is placed in the middle of the H-bridge so that it can accurately
measure current in both directions by using the shunt available
at the motor (see Figure 31). This is a better solution than a
ground referenced op amp because ground is not typically a
stable reference voltage in this type of application. This instability
in the ground reference causes the measurements that could be
made with a simple ground referenced op amp to be inaccurate.
The AD8216 measures current in both directions as the H-bridge
switches and the motor changes direction. The output of the
AD8216 is configured in an external reference bidirectional
mode (see the Output Offset Adjustment section).
+IN V
REF
1 V+ OUT
–IN
GND V
REF
2 NC
AD8216
SHUNT
5V
2.5V
5V
CONTROLLER
NC = NO CONNECT
MOTOR
07062-036
Figure 31. Motor Control Application
