AD8203MSOP(RevD) View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
AD8203MSOP Datasheet PDF : 20 Pages
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AD8203
APPLICATIONS
The AD8203 difference amplifier is intended for applications
that require extracting a small differential signal in the presence
of large common-mode voltages. The input resistance is nominally
320 kΩ, and the device can tolerate common-mode voltages
higher than the supply voltage and lower than ground.
The open collector output stage sources current to within
20 mV of ground and to within 200 mV of VS.
CURRENT SENSING
High Line, High Current Sensing
Basic automotive applications making use of the large common-
mode range are shown in Figure 2 and Figure 3. The capability
of the device to operate as an amplifier in primary battery sup-
ply circuits is shown in Figure 2. Figure 3 illustrates the ability
of the device to withstand voltages below system ground.
Low Current Sensing
The AD8203 is also used in low current sensing applications,
such as the 4 to 20 mA current loop shown in Figure 42. In such
applications, the relatively large shunt resistor can degrade the
common-mode rejection. Adding a resistor of equal value on the
low impedance side of the input corrects this error.
10Ω
1%
5V
+IN +VS NC OUT
OUTPUT
+
10Ω
1%
AD8203
–IN GND A1 A2
NC = NO CONNECT
Figure 42. 4 to 20 mA Current Loop Receiver
GAIN ADJUSTMENT
The default gain of the preamplifier and buffer are ×7 and ×2,
respectively, resulting in a composite gain of ×14. With the
addition of external resistor(s) or trimmer(s), the gain can be
lowered, raised, or finely calibrated.
Gains Less Than 14
Since the preamplifier has an output resistance of 100 kΩ, an
external resistor connected from Pin 3 and Pin 4 to GND
decreases the gain by a factor REXT/(100 kΩ + REXT), as shown
in Figure 43.
Data Sheet
VCM
VDIFF
2
VDIFF
2
+VS
+IN +VS NC OUT
OUT
10kΩ 10kΩ
AD8203
100kΩ
GAIN = 14REXT
REXT + 100kΩ
REXT =
100kΩ
GAIN
14 – GAIN
–IN GND A1 A2
REXT
NC = NO CONNECT
Figure 43. Adjusting for Gains < 14
The overall bandwidth is unaffected by changes in gain by using
this method, although there may be a small offset voltage due to
the imbalance in source resistances at the input to the buffer.
This can often be ignored, but if desired, it can be nulled by
inserting a resistor equal to 100 kΩ minus the parallel sum of
REXT and 100 kΩ, in series with Pin 4. For example, with
REXT = 100 kΩ (yielding a composite gain of ×7), the optional
offset nulling resistor is 50 kΩ.
Gains Greater Than 14
Connecting a resistor from the output of the buffer amplifier to
its noninverting input, as shown in Figure 44, increases the
gain. The gain is now multiplied by the factor REXT/(REXT −
100 kΩ); for example, the gain is doubled for REXT = 200 kΩ.
Overall gains as high as 50 are achievable this way. Note that the
accuracy of the gain becomes critically dependent on the
resistor value at high gains. Also, the effective input offset
voltage at Pin 1 and Pin 8 (about six times the actual offset of
A1) limits the part’s use in high gain, dc-coupled applications.
+VS
OUT
VCM
VDIFF
2
VDIFF
2
+IN +VS NC OUT
10kΩ 10kΩ
AD8203
100kΩ
REXT
GAIN = 14REXT
REXT – 100kΩ
REXT = 100kΩ
GAIN
GAIN – 14
–IN GND A1 A2
NC = NO CONNECT
Figure 44. Adjusting for Gains > 14
Rev. D | Page 14 of 20
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