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AD8218BCPZ-RL

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17
Data Sheet AD8218
Rev. B | Page 9 of 16
INPUT
OUTPUT
50V/DIV
1V/DIV
500ns/DIV
09592-019
Figure 22. Common-Mode Step Response, Rising
INPUT
OUTPUT
50V/DIV
1V/DIV
1µs/DIV
09592-020
Figure 23. Common-Mode Step Response, Falling
180
90
120
150
30
60
0
–200 –100 0 100 200
09592-021
COUNT
V
OSI
(µV)
Figure 24. Input Offset Distribution
500
300
400
100
200
0
–4 –2 0 2 4
09592-022
COUNT
GAIN DRIFT (ppm/°C)
1 3–1–3
Figure 25. Gain Drift Distribution
140
80
100
120
20
60
0
–0.6
–0.4 0 0.2
0.6
09592-023
COUNT
OFFSET DRIFT (µV/°C)
40
0.4
–0.2
Figure 26. Input Offset Drift Distribution
150
200
250
50
100
0
–5 0 5
10 15
09592-024
COUNT
INTERNAL REF OFFSET DRIFT (µV/°C)
Figure 27. Internal REF Offset Drift Distribution,
Referred to Output (RTO)
AD8218 Data Sheet
Rev. B | Page 10 of 16
THEORY OF OPERATION
AMPLIFIER CORE
In typical applications, the AD8218 amplifies a small differential
input voltage generated by the load current flowing through
a shunt resistor. The AD8218 rejects high common-mode vol-
tages (up to 80 V) and provides a ground-referenced, buffered
output. Figure 28 shows a simplified schematic of the AD8218.
V
REF
LOAD
V
2
I
LOAD
V
1
SHUNT
4V
TO
80V
I
CHARGE
GND
5V
LDO
R2
R1
AD8218
R4
R3
+IN
–IN
OUT
ENB
REF
GND
V
S
C
F
09592-027
Figure 28. Simplified Schematic
The AD8218 is configured as a difference amplifier. The
transfer function is
OUT = ((R4/R1) × (V
1
− V
2
)) + V
REF
Resistors R4 and R1 are matched to within 0.01% and have
values of 1.5 MΩ and 75 kΩ, respectively, meaning an input-
to-output total gain of 20 V/V for the AD8218. The difference
between V
1
and V
2
is the voltage across the shunt resistor, or
V
IN
. Therefore, the input-to-output transfer function of the
AD8218 is
OUT (V) = (20 × V
IN
) + V
REF
The AD8218 accurately amplifies the input differential signal,
rejecting high voltage common modes ranging from 4 V to 80 V.
The main amplifier uses a novel zero-drift architecture, providing
the end user with breakthrough temperature stability. The
offset drift is typically less than ±100 nV/°C. This performance
leads to optimal accuracy and dynamic range.
OUTPUT CLAMPING
After the input common-mode voltage in the application is
above 5.2 V, the internal LDO output of the AD8218 also
reaches its maximum value of 5.2 V, which is the maximum
output range of the AD8218. Because in typical applications
the output interfaces with a converter, clamping the AD8218
output voltage to 5.2 V ensures that the ADC input is not
damaged due to excessive overvoltage.
Data Sheet AD8218
Rev. B | Page 11 of 16
APPLICATION NOTES
SUPPLY (V
S
) CONNECTIONS
The AD8218 includes an internal LDO, which allows the user
to leave the V
S
pin floating, powering the AD8218 directly from
the voltage present at Pin 1 (+IN), provided this voltage is in the
4 V to 80 V range. A typical connection for the part in this
configuration is shown in Figure 29.
+IN
I
LOAD
V
S
SHUNT
GND
–IN
REF
LOAD
4V
TO
80V
2.5V
BATTER
Y
AD8218
OUT
I
CHARGE
ENB
09592-028
Figure 29. Operation with No V
S
Connection
The AD8218 can also be powered from a separate low impedance
supply at Pin 2 (V
S
); however, this voltage can only be in the 4 V
to 5.5 V range. In cases where the high voltage bus is susceptible
to noise, transients, or high voltage fluctuations and a 5 V supply is
available, the AD8218 can be used in the mode depicted in
Figure 30.
+IN
I
LOAD
V
S
SHUNT
GND
–IN
REF
LOAD
4V
TO
80V
BATTERY
AD8218
OUT
I
CHARGE
ENB
5V 2.5V
C
F
09592-029
Figure 30. 5 V Supply Operation
ENABLE PIN (ENB) OPERATION
The AD8218 includes an internal reference that can be enabled
by connecting Pin 3 (ENB) to ground. This mode of operation
is shown in Figure 31.
+IN
I
LOAD
V
S
SHUNT
GND
–IN
REF
LOAD
4V
T
O
80V
BATTE
R
Y
AD8218
OUT
ENB
09592-030
Figure 31. Enabling the Internal 80 mV Reference
In this configuration, the internal 80 mV reference is activated,
and the output of the AD8218 is 80 mV when the differential
input voltage is 0 V and the voltage at Pin 7 (REF) is also 0 V. This
internal reference is useful in unidirectional current measurements
where the current being monitored has a very wide range. Setting
the output starting point to 80 mV means that when the load
current through the shunt resistor is 0 A, the output is 80 m V.
This ensures that the output errors due to initial offset and the
output saturation range of the amplifier are overcome. In this
mode, the transfer function of the AD8218 becomes
OUT (V) = OUT (V) = (20 × V
IN
) + 0.08 V
If Pin 3 is connected to ground, and therefore the internal
reference is enabled, 80 mV must always be added to the
transfer function of the AD8218.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17

AD8218BCPZ-RL

Mfr. #:
Buy AD8218BCPZ-RL
Manufacturer:
Analog Devices Inc.
Description:
Current Sense Amplifiers 0-Drift BiDirectionl Current SenseAmp
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