Data Sheet

AD8418

APPLICATIONS INFORMATION

MOTOR CONTROL

3-Phase Motor Control

The AD8418 is ideally suited for monitoring current in 3-phase

motor applications.

The 250 kHz typical bandwidth of the AD8418 allows

instantaneous current monitoring. Additionally, the typical

low offset drift of 0.1 µV/°C means that the measurement error

between the two motor phases is at a minimum over temperature.

The AD8418 rejects PWM input common-mode voltages in the

−2 V to +70 V (with a 5 V supply) range. Monitoring the current

on the motor phase allows sampling of the current at any point

and provides diagnostic information such as a short to GND

and battery. Refer to Figure 33 for the typical phase current

measurement setup with the AD8418.

H-Bridge Motor Control

Another typical application for the AD8418 is as part of the

control loop in H-bridge motor control. In this case, the shunt

resistor 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 32). Using an amplifier

and shunt in this location is a better solution than a ground

referenced op amp because ground is not typically a stable

reference voltage in this type of application. The instability of

the ground reference causes inaccuracies in the measurements

that can be made with a simple ground referenced op amp. The

AD8418 measures current in both directions as the H-bridge

switches and the motor changes direction. The output of the

AD8418 is configured in an external referenced bidirectional

mode (see the Bidirectional Operation section).

AD8418

+IN

SHUNT

MOTOR

OUT

–IN

GND

5V

CONTROLLER

NC

5V

2.5V

Figure 32. H-Bridge Motor Control

AD8418

BIDIRECTIONAL CURRENT MEASUREMENT

REJECTION OF HIGH PWM COMMON-MODE VOLTAGE (–2V TO +70V)

AMPLIFICATION

HIGH OUTPUT DRIVE

AD8214

INTERFACE

CIRCUIT

V+

V–

OPTIONAL

PART FOR

OVERCURRENT

PROTECTION AND

FAST (DIRECT)

SHUTDOWN OF

POWER STAGE

AD8418

CONTROLLER

5V

5V

M

Figure 33. 3-Phase Motor Control

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