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AD8418WBRZ

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17
AD8418 Data Sheet
EXTERNAL REFERENCED OUTPUT
Tying both pins together and to a reference produces an output
equal to the reference voltage when there is no differential input
(see Figure 29). The output moves down from the reference
voltage when the input is negative, relative to the −IN pin, and
up when the input is positive, relative to the −IN pin.
–
+
R1
OUT
GND
V
S
V
REF
1
V
REF
2
AD8418
R2
R3
R4
–IN
+IN
2.5V
11546-027
Figure 29. External Referenced Output
SPLITTING THE SUPPLY
By tying one reference pin to V
S
and the other to the ground pin,
the output is set at half of the supply when there is no differential
input (see Figure 30). The benefit is that an external reference
is not required to offset the output for bidirectional current
measurement. Tying one reference pin to V
S
and the other to
the ground pin creates a midscale offset that is ratiometric to
the supply, which means that if the supply increases or decreases,
the output remains at half the supply. For example, if the supply
is 5.0 V, the output is at half scale or 2.5 V. If the supply increases by
10% (to 5.5 V), the output goes to 2.75 V.
–
+
R1
OUT
GND
V
S
V
REF
1
V
REF
2
AD8418
R2
R3
R4
–IN
+IN
11546-028
Figure 30. Split Supply
SPLITTING AN EXTERNAL REFERENCE
The internal reference resistors can be used to divide an external
reference by 2 with an accuracy of approximately 0.5%. Splitting
an external reference can be done by connecting one V
REF
x pin to
ground and the other V
REF
X pin to the reference (see Figure 31).
–
+
R1
OUT
GND
V
S
V
REF
1
V
REF
2
AD8418
R2
R3
R4
–IN
+IN
5V
11546-029
Figure 31. Split External Reference
Rev. 0 | Page 12 of 16
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
MOT
OR
V
REF
1
V
S
OUT
–IN
GND
5V
CONTROLLER
V
REF
2
NC
5V
2.5V
1
1546-030
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+
I
U
I
V
I
W
V–
OPTIONAL
PART FOR
OVERCURRENT
PROTECTIONAND
FAST (DIRECT)
SHUTDOWN OF
POWER STAGE
AD8418
CONTROLLER
5V 5V
M
11546-031
Figure 33. 3-Phase Motor Control
Rev. 0 | Page 13 of 16
AD8418 Data Sheet
SOLENOID CONTROL
High-Side Current Sense with a Low-Side Switch
In the case of a high-side current sense with a low-side switch,
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 34). 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 open, 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.
–IN
1
GND
2
V
REF
2
3
NC
4
+IN
8
V
REF
1
7
V
S
6
OUT
OUTPUT
5V
INDUCTIVE
LOAD
CLAMP
DIODE
BATTERY
SWITCH
SHUNT
NC = NO CONNECT.
+
–
5
AD8418
1
1546-032
Figure 34. Low-Side Switch
High-Side Current Sense with a High-Side Switch
The high-side current sense with a high-side switch configuration
minimizes the possibility of unexpected solenoid activation and
excessive corrosion (see Figure 35). In this case, 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 recirculating
current to be measured and to provide 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. In this case, when the
switch is open, the voltage reversal across the inductive load
causes the common-mode voltage to be held one diode drop
below ground by the clamp diode.
–IN
1
GND
2
V
REF
2
3
NC
4
+IN
8
V
REF
1
7
V
S
6
OUT
OUTPUT
5V
INDUCTIVE
LOAD
SHUNT
CLAMP
DIODE
BATTERY
SWITCH
NC = NO CONNECT.
+
–
5
AD8418
11546-033
Figure 35. High-Side Switch
High Rail Current Sensing
In the high rail, current sensing configuration, the shunt resistor is
referenced to the battery. High voltage is present at the inputs of
the current sense amplifier. When the shunt is battery referenced,
the AD8418 produces a linear ground referenced analog output.
Additionally, the AD8214 can be used to provide an overcurrent
detection signal in as little as 100 ns (see Figure 36). This feature
is useful in high current systems where fast shutdown in
overcurrent conditions is essential.
V
S
1
+IN
2
V
REG
3
NC
4
–IN
8
NC
7
GND
6
OUT
OUTPUT
OVERCURRENT
DETECTION (<100ns)
5V
SHUNT
INDUCTIVE
LOAD
SWITCH
CLAMP
DIODE
BATTERY
+
–
5
AD8214
NC = NO CONNECT.
–IN
1
GND
2
V
REF
2
3
NC
4
+IN
8
V
REF
1
7
V
S
6
OUT
5
AD8418
TOP VIEW
(Not to Scale)
11546-034
Figure 36. High Rail Current Sensing
Rev. 0 | Page 14 of 16
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17

AD8418WBRZ

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Buy AD8418WBRZ
Manufacturer:
Analog Devices Inc.
Description:
Current Sense Amplifiers Zero Drift ,Precision Current Sense AMP
Lifecycle:
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