AD8207
Rev. 0 | Page 15 of 16
SOLENOID CONTROL
High-Side Current Sense with a Low-Side Switch
Other typical applications for the AD8207 include current
monitoring for PWM control of solenoid openings. Typical
applications include hydraulic valve control, diesel injection
control, and actuator control.
In Figure 35, 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 35).
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 capabilities are 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.
AD8207
+IN
42V
BATTERY
CLAMP
DIODE
INDUCTIVE
LOAD
SHUNT
SWITCH
V
REF
1
+V
S
5V
OUT
–IN GND V
REF
2 RANGE
09160-018
Figure 35. 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 36). In
Figure 36, both the switch and the shunt are on the high side.
When the switch is off, the battery is removed from the load,
which prevents damage from potential shorts to ground, while
still allowing the recirculation 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 can 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. 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.
AD8207
+IN
42V
BATTERY
CLAMP
DIODE
INDUCTIVE
LOAD
SHUNT
SWITCH
V
REF
1
+V
S
5V
OUT
–IN GND V
REF
2 RANGE
09160-019
Figure 36. High-Side Switch
