Datasheet

INA217
6
SBOS247B
www.ti.com
FIGURE 2. Input Stabilization Network.
V+
V–
V
O
2
1
8
3
5
4
6
7
V
IN
–
V
IN
+
INA217
47Ω
47Ω
1.2µH
1.2µH
APPLICATIONS INFORMATION
Figure 1 shows the basic connections required for operation.
Power supplies should be bypassed with 0.1µF tantalum
capacitors near the device pins. The output Reference (pin 5)
should be a low-impedance connection. Resistance of a few
ohms in series with this connection will degrade the com-
mon-mode rejection of the INA217.
GAIN-SET RESISTOR
Gain is set with an external resistor, R
G
, as shown in Figure 1.
The two internal 5kΩ feedback resistors are laser-trimmed to
5kΩ within approximately ±0.2%. The gain equation for the
INA217 is:
G
R
G
=+1
10 000,
The temperature coefficient of the internal 5kΩ resistors is
approximately ±25ppm/°C. Accuracy and TCR of the exter-
nal R
G
will also contribute to gain error and temperature drift.
These effects can be inferred from the gain equation. Make
a short, direct connection to the gain set resistor, R
G
. Avoid
running output signals near these sensitive input nodes
.
NOISE PERFORMANCE
The INA217 provides very low noise with low-source imped-
ance. Its 1.3nV/
√Hz voltage noise delivers near-theoretical
noise performance with a source impedance of 200Ω. The
input stage design used to achieve this low noise results in
FIGURE 1. Basic Circuit Connections.
relatively high input bias current and input bias current noise.
As a result, the INA217 may not provide the best noise
performance with a source impedance greater than 10kΩ.
For source impedance greater than 10kΩ, other instrumen-
tation amplifiers may provide improved noise performance.
INPUT CONSIDERATIONS
Very low source impedance (less than 10Ω) can cause the
INA217 to oscillate. This depends on circuit layout, signal
source, and input cable characteristics. An input network
consisting of a small inductor and resistor, as shown in
Figure 2, can greatly reduce any tendency to oscillate. This
is especially useful if a variety of input sources are to be
connected to the INA217. Although not shown in other
figures, this network can be used as needed with all applica-
tions shown.
A1
A2
A3
6kΩ 6kΩ
6
5
4
7
2
1
8
3
6kΩ 6kΩ
V
IN
–
V
IN
+
R
G
V+
V–
V+
V–
INA217
G = 1 +
10000
R
G
5kΩ
5kΩ
V
OUT
V
O
Sometimes Shown in
Simplified Form: NOTE: (1) NC = No Connection.
REF
0.1µF
0.1µF
R
G
INA217
GAIN R
G
(V/V) (dB) (Ω)
10NC
(1)
2 6 10000
5 14 2500
10 20 1111
20 26 526
50 34 204
100 40 101
200 46 50
500 54 20
1000 60 10
2000 66 5
V
IN
–
V
IN
+