AD8216

Rev. 0 | 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.

OUT

–IN

INDUCTIVE

LOAD

AD8216

CLAMP

DIODE

42V

BATTERY

SHUNT

SWITCH

NC = NO CONNECT

5V

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.

OUT

–IN

INDUCTIVE

LOAD

AD8216

CLAMP

DIODE

42V

BATTERY

SHUNT

SWITCH

NC = NO CONNECT

5V

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).

OUT

–IN

AD8216

SHUNT

5V

2.5V

5V

CONTROLLER

NC = NO CONNECT

MOTOR

Figure 31. Motor Control Application