INA156A Burr-Brown Corporation, INA156A Datasheet - Page 9

• Manufacturer Part Number: INA156A
• Description: Single-Supply/ Rail-to-Rail Output/ CMOS INSTRUMENTATION AMPLIFIER
• Manufacturer: Burr-Brown Corporation

SETTING THE GAIN
Gain of 10 is achieved simply by leaving the two gain pins
(1 and 8) open. Gain of 50 is achieved by connecting the
gain pins together directly. In the G = 10 configuration, the
gain error is less than 0.4%. In the G = 50 configuration, the
gain error is less than 0.8%.
Gain can be set to any value between 10 and 50 by connect-
ing a resistor R
following equation:
This is demonstrated in Figure 1 and is shown with the com-
monly used gains and resistor R
absolute value of internal resistors is not guaranteed, using the
INA156 in this configuration will increase the gain error and
gain drift with temperature, as shown in Figure 3.
OFFSET TRIMMING
Offset voltage can be adjusted by applying a correction
voltage to the reference terminal. Figure 4 shows an optional
circuit for trimming the output offset voltage. The voltage
applied to the Ref terminal is added to the output signal. An
op amp buffer is used to provide low impedance at the Ref
terminal to preserve good common-mode rejection.
FIGURE 4. Optional Trimming of Output Offset Voltage.
FIGURE 3. Typical Gain Error and Gain Error Drift with
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
NOTES: (1) V
level. The value of V
range. (2) For best performance, common-mode input voltage
should be less than (V+) – 1.8V or greater than (V+) – 0.8V.
0
V
V
IN
IN
+
10
–
(2)
(2)
Gain Drift
External Resistor.
15
10 + 400k /(10k
1
8
3
2
Gain Error
G
REF
20
between the gain pins according to the
INA156
should be adjusted for the desired output
5
Ref
25
REF
Gain (V/V)
(1)
affects the common-mode input
30
6
G
OPA336
values. However, because the
+ R
35
V
O
G
)
40
Adjustable
Voltage
45
50
400
360
320
280
250
200
160
120
80
40
0
(1)
9
FIGURE 5. Providing an Input Common-Mode Current Path.
INPUT BIAS CURRENT RETURN
The input impedance of the INA156 is extremely high—
approximately 10
ance sources. However, a path must be provided for the input
bias current of both inputs. This input bias current is less than
10pA and is virtually independent of the input voltage.
Input circuitry must provide a path for this input bias current
for proper operation. Figure 5 shows various provisions for
an input bias current path. Without a bias current path, the
inputs will float to a potential that exceeds the common-
mode range and the input amplifier will saturate.
If the differential source resistance is low, the bias current
return path can be connected to one input (see the thermo-
couple in Figure 5). With higher source impedance, using
two equal resistors provides a balanced input with advan-
tages of lower input offset voltage due to bias current and
better high-frequency common-mode rejection.
Hydrophone, etc.
Thermocouple
Microphone,
Sensor
Bridge
47k
13
, making it ideal for use with high-imped-
10k
47k
INA156
2
3
8
3
1
8
2
3
8
3
1
8
2
1
2
1
INA156
INA156
INA156
INA156
V
V
V
5
5
5
5
V
REF
REF
REF
REF
Bridge resistance
current return
Low-resistance
provides bias
current return.
thermocouple
provides bias
provides bias
current return
Center-tap
6
6
6
6
®