Datasheet

+
20 kΩ 380 kΩ
380 kΩ
380 kΩ
19 kΩ
−15 V
15 V
4 7
2
3
1
6
5
−IN
+IN V
OUT
= (+IN) − (−IN)
+
15 V
−15 V
100 Ω
100 Ω
100 µA
½ REF200
100 µA
½ REF200
10 kΩ
(1)
INA149
SBOS579B SEPTEMBER 2011REVISED JULY 2012
www.ti.com
COMMON-MODE REJECTION
Common-mode rejection (CMR) of the INA149 depends on the input resistor network, which is laser-trimmed for
accurate ratio matching. To maintain high CMR, it is important to have low source impedance driving the two
inputs. A 75-Ω resistance in series with pins 2 or 3 decreases the common-mode rejection ratio (CMRR) from
100 dB (typical) to 74 dB.
Resistance in series with the reference pins also degrades CMR. A 4-Ω resistance in series with pins 1 or 5
decreases CMRR from 100 dB to 74 dB.
Most applications do not require trimming. Figure 45 shows an optional circuit that may be used for trimming
offset voltage and common-mode rejection.
(1) The OPA171 (a 36-V, low-power, RRO, general-purpose operational amplifier) can be used for this application.
Figure 45. Offset Voltage Trim Circuit
14 Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated
Product Folder Link(s): INA149