AD8211

Rev. A | Page 12 of 16

APPLICATIONS INFORMATION

HIGH-SIDE CURRENT SENSE WITH A LOW-SIDE

SWITCH

In such load control configurations, the PWM-controlled

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 25). 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.

GND

2

1

5

OUT

V+

3

4

AD8211

5V

INDUCTIVE

LOAD

CLAMP

DIODE

SHUNT

SWITCH

BATTERY

1

2

3

5

4

Figure 25. Low-Side Switch

HIGH-SIDE CURRENT SENSING

In this configuration, the shunt resistor is referenced to the

battery. High voltage is present at the inputs of the current sense

amplifier. In this mode, the recirculation current is again measured

and shorts to ground can be detected. When the shunt is battery

referenced, the AD8211 produces a linear ground-referenced

analog output. An AD8214 can also be used to provide an over-

current detection signal in as little as 100 ns. This feature is

useful in high current systems where fast shutdown in over-

current conditions is essential.

GND

2

1

5

OUT

V+

3

4

AD8211

5V

INDUCTIVE

LOAD

CLAMP

DIODE

SHUNT

SWITCH

BATTERY

1

2

3

4

8

7

6

5

AD8214

GND

NC

–IN

OUT

+IN

NC

OVERCURRENT

DETECTION (<100ns)

1

2

3

5

4

Figure 26. Battery-Referenced Shunt Resistor

LOW-SIDE CURRENT SENSING

In systems where low-side current sensing is preferred, the

AD8211 provides an integrated solution with great accuracy.

Ground noise is rejected, CMRR is typically higher than 90 dB,

and output linearity is not compromised, regardless of the input

differential voltage.

GND

2

1

5

OUT

V+

3

4

AD8211

5V

INDUCTIVE

LOAD

CLAMP

DIODE

SHUNT

BATTERY

SWITCH

1

2

3

5

4

Figure 27. Ground-Referenced Shunt Resistor