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

5V

OUT

–IN

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

5V

OUT

–IN

Figure 36. High-Side Switch