AD8210
APPLICATIONS
A typical application for the AD8210 is high-side measurement
of a current through a solenoid for PWM control of the sole-
noid opening. Typical applications include hydraulic transmis-
sion control and diesel injection control.
Two typical circuit configurations are used for this type of
application.
Preliminary Technical Data
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.
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 7).
An advantage of placing the shunt on the high side is that the
entire current, including the re-circulation current, can be
measured since 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.
5V
42V
BATTERY
SWITCH
+IN V
REF
1 +V
S
SHUNT
鈥揑N
CLAMP
DIODE
INDUCTIVE
LOAD
NC = NO CONNECT
OUT
AD8210
GND V
REF
2 NC
Figure 8. High-Side Switch
CLAMP
DIODE
42V
BATTERY
SHUNT
INDUCTIVE
LOAD
+IN V
REF
1 +V
S
OUT
AD8210
鈥揑N
GND V
REF
2 NC
Another typical application for the AD8210 is as part of the
control loop in H-bridge motor control. In this case, the
AD8210 is placed in the middle of the H-bridge (see Figure 9)
so that it can accurately measure current in both directions by
using the shunt available at the motor. This is a better solution
than a ground referenced op amp because ground is not typi-
cally 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 AD8210 measures current in both directions as the
H-bridge switches and the motor changes direction. The output
of the AD8206 is configured in an external reference bidirec-
tional mode, see the Output Offset Adjustment section.
SWITCH
NC = NO CONNECT
04953-019
Figure 7. Low-Side Switch
5V
CONTROLLER
HIGH-SIDE CURRENT SENSE WITH A HIGH-SIDE
SWITCH
This configuration minimizes the possibility of unexpected
solenoid activation and excessive corrosion (see Figure 8). In
this case, both the switch and the shunt are on the high side.
When the switch is off, this removes the battery from the load,
which prevents damage from potential shorts to ground, while
still allowing the recirculation current to be measured and pro-
viding 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.
MOTOR
+IN
V
REF
1 +V
S
OUT
AD8210
SHUNT
鈥揑N
GND V
REF
2 NC
5V
2.5V
NC = NO CONNECT
Figure 9. Motor Control Application
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