AD8218

Rev. A | Page 11 of 16

APPLICATION NOTES

The AD8218 includes an internal LDO, which allows the user

the voltage present at Pin 1 (+IN), provided this voltage is in the

4 V to 80 V range. A typical connection for the part in this

configuration is shown in Figure 28.

+IN

SHUNT

GND

–IN

REF

LOAD

4V

TO

80V

2.5V

BATTERY

AD8218

OUT

ENB

The AD8218 can also be powered from a separate low impedance

to 5.5 V range. In cases where the high voltage bus is susceptible

to noise, transients, or high voltage fluctuations and a 5 V supply is

available, the AD8218 can be used in the mode depicted in

Figure 29.

+IN

SHUNT

GND

–IN

REF

LOAD

4V

TO

80V

BATTERY

AD8218

OUT

ENB

5V

2.5V

Figure 29. 5 V Supply Operation

ENABLE PIN (ENB) OPERATION

The AD8218 includes an internal reference that can be enabled

by connecting Pin 3 (ENB) to ground. This mode of operation

is shown in Figure 30.

+IN

SHUNT

GND

–IN

REF

LOAD

4V

TO

80V

BATTERY

AD8218

OUT

ENB

Figure 30. Enabling the Internal 80 mV Reference

In this configuration, the internal 80 mV reference is activated,

and the output of the AD8218 is 80 mV when the differential

input voltage is 0 V and the voltage at Pin 7 (REF) is also 0 V. This

internal reference is useful in unidirectional current measurements

where the current being monitored has a very wide range. Setting

the output starting point to 80 mV means that when the load

current through the shunt resistor is 0 A, the output is 80 mV.

This ensures that the output errors due to initial offset and the

output saturation range of the amplifier are overcome. In this

mode, the transfer function of the AD8218 becomes

If Pin 3 is connected to ground, and therefore the internal

reference is enabled, 80 mV must always be added to the

transfer function of the AD8218.