Datasheet

AD8270
Rev. 0 | Page 15 of 20
APPLICATIONS INFORMATION
DIFFERENCE AMPLIFIER CONFIGURATIONS
The AD8270 can be placed in difference amplifier configurations
with gains of 0.5, 1, and 2.
Figure 42 through Figure 44 show the
difference amplifier configurations, referenced to ground. The
AD8270 can also be referred to a combination of reference voltages.
For example, the reference could be set at 2.5 V, using just 5 V
and GND. Some of the possible configurations are shown in
Figure 45 through Figure 47.
The layout for Channel A is shown in
Figure 42 through Figure 47.
The layout for Channel B is symmetrical.
Table 7 shows the pin
connections for Channel A and Channel B.
SINGLE-ENDED CONFIGURATIONS
The AD8270 can be configured for a wide variety of single-
ended configurations with gains ranging from −2 to +3.
Table 8 shows a subset of the possible configurations.
Many signal gains have more than one configuration choice,
which allows freedom in choosing the op amp closed-loop gain.
In general, for designs that need to be stable with a large capacitive
load on the output, choose a configuration with high loop gain.
Otherwise, choose a configuration with low loop gain, because
these configurations typically have lower noise, lower offset,
and higher bandwidth.
10kΩ 10kΩ
10kΩ
10kΩ
10kΩ
20kΩ 20kΩ
1
2
3
4
16 15
56
=
–IN
+IN
–
IN
+IN
5kΩ
5kΩ
10kΩ
10kΩ
GND
GND
06979-053
Figure 42. Gain = 0.5 Difference Amplifier, Referenced to Ground
=
–IN
+IN
10kΩ
10kΩ
10kΩ
10kΩ
GND
–IN
+IN
GND
10kΩ 10kΩ
10kΩ
10kΩ
10kΩ
20kΩ 20kΩ
1
2
3
4
16 15
56
NC
NC
NC = NO CONNECT
06979-054
Figure 43. Gain = 1 Difference Amplifier, Referenced to Ground
=
–IN
+IN
10kΩ
5kΩ
5kΩ
10kΩ
GND
–IN
+IN
GND
10kΩ 10kΩ
10kΩ
10kΩ
10kΩ
20kΩ 20kΩ
1
2
3
4
16 15
56
06979-055
Figure 44. Gain = 2 Difference Amplifier, Referenced to Ground
+V
S
+ –V
S
2
–IN
+IN
–V
S
+V
S
10kΩ 10kΩ
10kΩ
10kΩ
10kΩ
20kΩ 20kΩ
1
2
3
4
16 15
56
=
–IN
+IN
5kΩ
5kΩ
10kΩ
10kΩ
06979-056
Figure 45. Gain = 0.5 Difference Amplifier, Referenced to Midsupply
=
–IN
+IN
10kΩ
10kΩ
10kΩ
10kΩ
+V
S
+ –V
S
2
–IN
+IN
–V
S
+V
S
NC
NC
10kΩ 10kΩ
10kΩ
10kΩ
10kΩ
20kΩ 20kΩ
1
2
3
4
16 15
56
NC = NO CONNECT
06979-057
Figure 46. Gain = 1 Difference Amplifier, Referenced to Midsupply
=
–IN
+IN
10kΩ
5kΩ
5kΩ
10kΩ
+V
S
+ –V
S
2
–
IN
+IN
–V
S
+V
S
10kΩ 10kΩ
10kΩ
10kΩ
10kΩ
20kΩ 20kΩ
1
2
3
4
16 15
56
06979-058
Figure 47. Gain = 2 Difference Amplifier, Referenced to Midsupply
Table 7. Pin Connections for Difference Amplifier Configurations
Channel A Channel B
Gain and Reference Pin 1 Pin 2 Pin 3 Pin 4 Pin 5 Pin 6 Pin 12 Pin 11 Pin 10 Pin 9 Pin 8 Pin 7
Gain of 0.5, Referenced to Ground OUT −IN +IN GND GND GND OUT −IN +IN GND GND GND
Gain of 0.5, Referenced to Midsupply OUT −IN +IN −V
S
+V
S
+V
S
OUT −IN +IN −V
S
+V
S
+V
S
Gain of 1, Referenced to Ground −IN NC NC +IN GND GND −IN NC NC +IN GND GND
Gain of 1, Referenced to Midsupply −IN NC NC +IN −V
S
+V
S
−IN NC NC +IN −V
S
+V
S
Gain of 2, Referenced to Ground −IN −IN +IN +IN GND GND −IN −IN +IN +IN GND GND
Gain of 2, Referenced to Midsupply −IN −IN +IN +IN −V
S
+V
S
−IN −IN +IN +IN −V
S
+V
S