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AD8418ABRMZ

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17
Data Sheet AD8418A
Rev. B | Page 13 of 17
EXTERNAL REFERENCED OUTPUT
Tying V
REF
1 and V
REF
2 together and to a reference produces an
output equal to the reference voltage when there is no differential
input (see Figure 31). The output decreases the reference voltage
when the input is negative, relative to the −IN pin, and increases
the voltage when the input is positive, relative to the −IN pin.
–
+
R1
OUT
GND
V
S
V
REF
1
V
REF
2
AD8418A
R2
R3
R4
–IN
+IN
2.5V
11883-027
Figure 31. 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 32). The benefit of this configuration 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 increases
to 2.75 V.
–
+
R1
OUT
GND
V
S
V
REF
1
V
REF
2
AD8418A
R2
R3
R4
–IN
+IN
11883-028
Figure 32. Split Supply
SPLITTING AN EXTERNAL REFERENCE
Use the internal reference resistors to divide an external reference
by 2 with an accuracy of approximately 0.5%. Split an external
reference by connecting one V
REF
x pin to ground and the other
V
REF
x pin to the reference (see Figure 33).
–
+
R1
OUT
GND
V
S
V
REF
1
V
REF
2
AD8418A
R2
R3
R4
–IN
+IN
5V
11883-029
Figure 33. Split External Reference
AD8418A Data Sheet
Rev. B | Page 14 of 17
APPLICATIONS INFORMATION
MOTOR CONTROL
3-Phase Motor Control
The AD8418A is ideally suited for monitoring current in
3-phase motor applications.
The 250 kHz typical bandwidth of the AD8418A provides
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 AD8418A 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 35 for the typical phase
current measurement setup with the AD8418A.
H-Bridge Motor Control
Another typical application for the AD8418A is to form part of
the control loop in H-bridge motor control. In this case, place
the shunt resistor in the middle of the H-bridge to accurately
measure current in both directions by using the shunt available
at the motor (see Figure 34). 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 AD8418A measures
current in both directions as the H-bridge switches and the
motor changes direction. The output of the AD8418A is
configured in an external referenced bidirectional mode (see
the Bidirectional Operation section).
AD8418A
+IN
SHUNT
MOTOR
V
REF
1
V
S
OUT
–IN GND
5V
CONTROLLER
V
REF
2NC
5V
2.5V
11883-030
Figure 34. H-Bridge Motor Control
AD8418A
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
DEVICE FOR
OVERCURRENT
PROTECTION AND
FAST (DIRECT)
SHUTDOWN OF
POWER STAGE
AD8418A
CONTROLLER
5V 5V
M
11883-031
Figure 35. 3-Phase Motor Control
Data Sheet AD8418A
Rev. B | Page 15 of 17
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. Tie an inductive
load (solenoid) to a power supply and place a resistive shunt
between the switch and the load (see Figure 36). An advantage
of placing the shunt on the high side is that the entire current,
including the recirculation current, is measurable because the
shunt remains in the loop when the switch is off. In addition,
diagnostics are enhanced because shorts to ground are detected
with the shunt on the high side.
In this circuit configuration, when the switch is closed, the
common-mode voltage decreases 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
AD8418A
11883-032
Figure 36. 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 37). 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 that the
switch is open 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
AD8418A
11883-033
Figure 37. 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 AD8418A produces a linear ground referenced analog output.
Additionally, the AD8214 provides an overcurrent detection
signal in as little as 100 ns (see Figure 38). 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
AD8418A
TOP VIEW
(Not to Scale)
11883-034
Figure 38. High Rail Current Sensing
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17

AD8418ABRMZ

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Buy AD8418ABRMZ
Manufacturer:
Analog Devices Inc.
Description:
Current Sense Amplifiers High Common Mode Cur Sense -3V to 80V
Lifecycle:
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