Datasheet

8
®
INA146
APPLICATION INFORMATION
The INA146 is a programmable gain difference amplifier
consisting of a gain of 0.1 difference amplifier and a pro-
grammable-gain output buffer stage. Basic circuit connec-
tions are shown in Figure 1. Power supply bypass capacitors
should be connected close to pins 4 and 7 as shown. The
amplifier is programmable in the range of G = 0.1 to G = 50
with two external resistors.
The output of A1 is connected to the noninverting input of
A2 through a 10kΩ resistor which is trimmed to ±1%
absolute accuracy. The A2 input is available for applications
such as a filter or a precision current source. See application
figures for examples.
OPERATING VOLTAGE
The INA146 is fully specified for supply voltages from
±2.25V to ±18V with key parameters guaranteed over the
temperature range –40°C to +85°C. The INA146 can be
operated with single or dual supplies with excellent perfor-
mance. Parameters that vary significantly with operating
voltage, load conditions or temperature are shown in the
typical performance curves.
SETTING THE GAIN
The gain of the INA146 is set by using two external
resistors, R
G1
and R
G2
, according to the equation:
G = 0.1 • (1 + R
G2
/R
G1
)
For a total gain of 0.1, A2 is connected as a buffer amplifier
with no R
G1
. A feedback resistor, R
G2
= 10kΩ, should be
used in the buffer connection. This provides bias current
cancellation (in combination with internal R
5
) to assure
specified offset voltage performance. Commonly used val-
ues are shown in the table of Figure 1. Resistor values for
other gains should be chosen to provide a 10kΩ parallel
resistance.
COMMON-MODE RANGE
The 10:1 input resistor ratio of the INA146 provides an input
common-mode range that can extend well beyond the power
supply rails. Exact range depends on the power supply
voltage and the voltage applied to the Ref terminal (pin 1).
To assure proper operation, the voltage at the non-inverting
input of A1 (an internal node) must be within its linear
operating range. Its voltage is determined by the simple 10:1
voltage divider between pin 3 and pin 1. This voltage must
be between V– and (V+) – 1V.
FIGURE 1. Basic Circuit Connections.
R
5
10kΩ
A1
V
IN
INA146
V
O
R
2
10kΩ
R
1
100kΩ
V
IN
R
3
100kΩ
R
4
10kΩ
R
G1
R
G2
R
B
A2
V
01
7
3
2
5
418
6
–V
S
+V
S
0.1µF
–
+
V
O
= (V
IN
– V
IN
) 0.1 (1 + R
G2
/R
G1
)
+–
TOTAL GAIN A2 GAIN R
G1
R
G2
R
B
(V/V) (V/V) (Ω)(Ω)(Ω)
0.1 1 (None) 10k —
0.2 2 20k 20k —
0.5 5 12.4k 49.9k —
1 10 11.0k 100k —
2 20 10.5k 200k —
5 50 10.2k 499k —
10 100 10.2k 1M —
20 200 499 100k 9.53k
50 500 100 49.9k 10k
100 1000 100 100k 10k
STANDARD 1% RESISTORS
0.1µF