Datasheet

INA149
U1
+
19kΩ
380kΩ
20kΩ
380kΩ
380kΩ
B
REF
-IN
V-
+IN
A
REF
OUT
V
V+
NC
JMP4
GND
JMP3
JMP2
1 2 3 123
REFB REFA
1
2
U2
3
4
8
7
6
5
+
GND
GND
C5
C4
REFV-
REFV+
R8
R7
R4
R3
V-
V+
V+
R5
C8
GND
REF
SO-8
R9
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2.2 Reference Voltage Schematic
Figure 3 shows that the reference voltage can be applied to the INA149 in a variety of ways. The INA149
has two pins for reference voltages: REFA, REFB. Most applications require REFA and REFB to be
shorted. This functionality is accomplished with JMP4. In dual-supply applications, the reference voltages
are typically connected to ground. Connecting pins 2 and 3 of JMP2 and JPM3 accommodate this
configuration. For single-supply applications, It is often required to connect the reference voltages to
mid-supply. This can be accomplished by either applying a voltage directly to test point REFA (or test
point REFB) and shorting JMP4, or using the resistive divider created by R3 and R4. If a matched
precision resistor network is desired, a SOT-23 pad (R9) is located on the bottom of the board. When
using a resistor divider, however, the voltage must be buffered to ensure good common-mode rejection
(CMR). U2 is intended for a standard pinout operational amplifier in an SO-8 package. If U2 is to be
powered by the V+ and V– supplies, R7 and R8 should be populated with 0-Ω resistors; otherwise,
another supply can be connected to the REFV+ and REFV– test points. Recommendations for this
operational amplifier include the OPA376, OPA330, and OPA277.
Figure 3. INA149EVM Reference Voltage Schematic
5
SBOU119– November 2011 INA149EVM
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