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AD8418ABRMZ

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17
AD8418A Data Sheet
Rev. B | Page 10 of 17
–400
–
300
–200
–
100
0
100 200
300
400
0
200
400
600
800
1000
1200
1400
1600
V
OS
(µV)
HITS
–40°C
+25°C
+125°C
11883-325
V
S
= 5.0V
Figure 25. Offset Voltage Distribution
–40
–25
–10
5
20
35
50
65
80
95 110 125
TEMPERATURE (°C)
–0.5
–0.4
–0.3
–0.2
–0.1
0
0.1
0.2
0.3
0.4
0.5
CMRR (µV/V)
NORMALIZED AT 25°C
11883-024
Figure 26. CMRR vs. Temperature
–3
–2
–1
0 1
0
300
600
900
1200
1500
1800
GAIN ERROR DRIFT (ppm/
°C)
HITS
11883-023
Figure 27. Gain Error Drift Distribution
Data Sheet AD8418A
Rev. B | Page 11 of 17
THEORY OF OPERATION
The AD8418A 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 AD8418A measures current by
amplifying the voltage across a shunt resistor connected to its
inputs by a gain of 20 V/V (see Figure 28).
The AD8418A design provides excellent common-mode
rejection, even with PWM common-mode inputs that can change
at very fast rates, for example, 1 V/ns. The AD8418A contains
proprietary technology to eliminate the negative effects of such
fast changing external common-mode variations.
The AD8418A features an input offset drift of less than 400 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 AD8418A 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 AD8418A to
deliver total accuracy for these demanding applications.
+
I
SHUNT
G = 20
V
CM
= –2V TO +70
V
V
S
= 2.7V TO 5.5
V
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
AD8418A
V
S
+IN
–IN
–
GND
–50A
50A
R
SHUNT
11883-225
Figure 28. Typical Application
AD8418A Data Sheet
Rev. B | Page 12 of 17
OUTPUT OFFSET ADJUSTMENT
The output of the AD8418A can be adjusted for unidirectional
or bidirectional operation.
UNIDIRECTIONAL OPERATION
Unidirectional operation allows the AD8418A 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 decrease the output. If the output is
set at ground, the polarity must be positive to increase the output.
Ground Referenced Output Mode
When using the AD8418A in ground referenced output 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 29).
–
+
R1
OUT
GND
V
S
V
REF
1
V
REF
2
AD8418A
R2
R3
R4
–IN
+IN
11883-025
Figure 29. Ground Referenced Output
V
S
Referenced Output Mode
V
S
referenced output 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 30).
–
+
R1
OUT
GND
V
S
V
REF
1
V
REF
2
AD8418A
R2
R3
R4
–IN
+IN
1
1883-026
Figure 30. V
S
Referenced Output
BIDIRECTIONAL OPERATION
Bidirectional operation allows the AD8418A 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.
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
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