AD8200YCSURF AD [Analog Devices], AD8200YCSURF Datasheet - Page 6

• Manufacturer Part Number: AD8200YCSURF
• Description: High Common-Mode Voltage, Single-Supply Difference Amplifier
• Manufacturer: AD [Analog Devices]

AD8200
CURRENT SENSING
High Line, High Current Sensing
Basic automotive applications making use of the large common-
mode range are shown in Figures 1 and 2. The capability of the
device to operate as an amplifier in primary battery supply circuits
is shown in Figure 1; Figure 2 illustrates the ability of the device
to withstand voltages below system ground.
Low Current Sensing
The AD8200 can also be used in low current sensing applica-
tions, such as the 4–20 mA current loop shown in Figure 4. In
such applications, the relatively large shunt resistor can degrade
the common-mode rejection. Adding a resistor of equal value in
the low impedance side of the input corrects for this error.
GAIN ADJUSTMENT
The default gain of the preamplifier and buffer are 10 and
respectively, resulting in a composite gain of 20. With the
addition of external resistor(s) or trimmer(s), the gain may be
lowered, raised, or finely calibrated.
Gains Less than 20
Since the preamplifier has an output resistance of 100 kΩ, an exter-
nal resistor connected from Pins 3 and 4 to GND will decrease the
gain by a factor R
The overall bandwidth is unaffected by changes in gain using
this method, although there may be a small offset voltage due to
the imbalance in source resistances at the input to the buffer. In
many cases this can be ignored, but if desired, can be nulled by
inserting a resistor equal to 100 kΩ minus the parallel sum of
R
= 100 kΩ (yielding a composite gain of 10), the optional offset
nulling resistor is 50 kΩ (see Figure 11.)
EXT
V
CM
+
and 100 kΩ, in series with Pin 4. For example, with R
Figure 5. Adjusting for Gains Less than 20
Figure 4. 4–20 mA Current Loop Receiver
V
V
DIFF
DIFF
2
2
NC = NO CONNECT
EXT
/(100 kΩ + R
10
AD8200
1%
+IN
–IN
100k
10k
10
1%
GND
NC
+IN
–IN
EXT
10k
+V
+V
A1
S
S
) (see Figure 5).
AD8200
GND
NC
OUT
A2
R
+V
5V
A1
EXT
NC = NO CONNECT
S
GAIN =
R
OUT
A2
EXT
OUT
= 100k
R
EXT
OUTPUT
20R
+ 100k
20 – GAIN
EXT
GAIN
EXT
2,
–6–
Gains Greater than 20
Connecting a resistor from the output of the buffer amplifier to
its noninverting input, as shown in Figure 6, will increase the
gain. The gain is now multiplied by the factor R
100 kΩ); for example, it is doubled for R
gains as high as 50 are achievable in this way. Note that the
accuracy of the gain becomes critically dependent on resistor
value at high gains. Also, the effective input offset voltage at
Pins 1 and 8 (about six times the actual offset of A1) limits the
part’s use in very high gain, dc-coupled applications.
GAIN TRIM
Figure 7 shows a method for incremental gain trimming using a
trimpot and external resistor R
The following approximation is useful for small gain ranges
Thus, the adjustment range would be ± 2% for R
± 10% for R
V
CM
V
Figure 6. Adjusting for Gains Greater than 20
CM
V
V
DIFF
DIFF
2
2
NC = NO CONNECT
EXT
Figure 7. Incremental Gain Trim
V
V
= 1 MΩ, and so on.
DIFF
DIFF
2
2
NC = NO CONNECT
∆
AD8200
G
+IN
100k
–IN
10k
≈
GND
(
NC
10
+IN
–IN
M
+V
10k
+V
A1
EXT
S
S
Ω
GND
AD8200
NC
.
OUT
÷
A2
R
5V
+V
A1
EXT
S
OUT
A2
EXT
R
R
)
EXT
EXT
%
= 200 kΩ. Overall
GAIN =
R
EXT
EXT
EXT
GAIN TRIM
20k
OUT
= 100k
/(R
R
OUT
= 5 MΩ;
EXT
MIN
EXT
20R
REV. B
– 100k
GAIN – 20
EXT
–
GAIN