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AD8418WBRZ

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17
Data Sheet AD8418
–500
–450
–400
–350
–300
–250
–200
–150
–100
–50
0
0 1 2 3 4 5 6 7 8 9 10
VOLTAGE FROM POSITIVE RAI
L (mV)
OUTPUT SOURCE CURRENT (mA)
11546-021
Figure 21. Output Voltage Range from Positive Rail vs. Output Source Current
0
20
40
60
80
100
120
140
160
180
200
1 2
3 4 5 6 7 8 9 10
VOLTAGE FROM GROUND (mV)
OUTPUT SINK CURRENT (mA)
11546-022
Figure 22. Output Voltage Range from Ground vs. Output Sink Current
V
OS
(µV)
V
S
= 5V
–400 –300
–200
–100
0
100
200
300
400
0
300
600
900
1200
1500
1800
HITS
11546-024
+125°C
+25°C
–40°C
Figure 23. Offset Voltage Distribution
–0.4
–0.3
–0.2
–0.1
0
0.1
0.2
0.3
0.4
–40 –25 –10 5 20 35 50 65 80 95 110 125
CMRR (µV/V)
TEMPERATURE
(°C)
11546-023
Figure 24. CMRR vs. Temperature
–8
–6
–4
–2
0 2
4
6
8
0
300
600
900
1200
1500
1800
GAIN ERROR DRIFT
(PPM/°C)
1
1546-125
HITS
Figure 25. Gain Drift Distribution
Rev. 0 | Page 9 of 16
AD8418 Data Sheet
THEORY OF OPERATION
The AD8418 is a single-supply, zero drift, difference amplifier
that uses a unique architecture to accurately amplify small
differential current shunt voltages in the presence of rapidly
changing common-mode voltages.
In typical applications, the AD8418 is used to measure current
by amplifying the voltage across a shunt resistor connected to its
inputs by a gain of 20 V/V (see Figure 26).
The AD8418 is designed to provide excellent common-mode
rejection, even with PWM common-mode inputs that can change
at very fast rates, for example, 1 V/ns. The AD8418 contains
patented technology to eliminate the negative effects of such
fast changing external common-mode variations.
The AD8418 features an input offset drift of less than 500 nV/°C.
This performance is achieved through a novel zero drift
architecture that does not compromise bandwidth, which is
typically rated at 250 kHz.
The reference inputs, V
REF
1 and V
REF
2, are tied through 100 kΩ
resistors to the positive input of the main amplifier, which allows
the output offset to be adjusted anywhere in the output operating
range. The gain is 1 V/V from the reference pins to the output
when the reference pins are used in parallel. When the pins are
used to divide the supply, the gain is 0.5 V/V.
The AD8418 offers breakthrough performance without
compromising any of the robust application needs typical of
solenoid or motor control. The ability to reject PWM input
common-mode voltages and the zero drift architecture
providing low offset and offset drift allows the AD8418 to
deliver total accuracy for these demanding applications.
+
I
SHUNT
G = 20
V
CM
= –2V TO +70V V
S
= 2.7V TO 5.5V
V
REF
1
V
REF
2
OUT
0V
V
S
V
S
/2
V
OUT
I
SHUNT
EMI
FILTER
EMI
FILTER
V
CM
0V
70V
AD8418
V
S
+IN
–IN
–
GND
–50A
50A
R
SHUNT
11546-225
Figure 26. Typical Application
Rev. 0 | Page 10 of 16
Data Sheet AD8418
OUTPUT OFFSET ADJUSTMENT
The output of the AD8418 can be adjusted for unidirectional or
bidirectional operation.
UNIDIRECTIONAL OPERATION
Unidirectional operation allows the AD8418 to measure currents
through a resistive shunt in one direction. The basic modes for
unidirectional operation are ground referenced output mode
and V
S
referenced output mode.
For unidirectional operation, the output can be set at the negative
rail (near ground) or at the positive rail (near V
S
) when the
differential input is 0 V. The output moves to the opposite rail
when a correct polarity differential input voltage is applied. The
required polarity of the differential input depends on the output
voltage setting. If the output is set at the positive rail, the input
polarity needs to be negative to move the output down. If the
output is set at ground, the polarity must be positive to move
the output up.
Ground Referenced Output
When using the AD8418 in this mode, both referenced inputs are
tied to ground, which causes the output to sit at the negative rail
when there are zero differential volts at the input (see Figure 27).
–
+
R1
OUT
GND
V
S
V
REF
1
V
REF
2
AD8418
R2
R3
R4
–IN
+IN
11546-025
Figure 27. Ground Referenced Output
V
S
Referenced Output
This mode is set when both reference pins are tied to the positive
supply. It is typically used when the diagnostic scheme requires
detection of the amplifier and the wiring before power is applied to
the load (see Figure 28).
–
+
R1
OUT
GND
V
S
V
REF
1
V
REF
2
AD8418
R2
R3
R4
–IN
+IN
11546-026
Figure 28. V
S
Referenced Output
BIDIRECTIONAL OPERATION
Bidirectional operation allows the AD8418 to measure currents
through a resistive shunt in two directions.
In this case, the output is set anywhere within the output range.
Typically, it is set at half-scale for equal range in both directions.
In some cases, however, it is set at a voltage other than half scale
when the bidirectional current is nonsymmetrical.
Adjusting the output is accomplished by applying voltage(s) to
the referenced inputs.
V
REF
1 and V
REF
2 are tied to internal resistors that connect to an
internal offset node. There is no operational difference between
the pins.
Rev. 0 | Page 11 of 16
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17

AD8418WBRZ

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