![](http://datasheet.mmic.net.cn/230000/INA125UA_datasheet_15584750/INA125UA_12.png)
12
INA125
amount of supply voltage headroom available to the refer-
ence. Approximately 180
μ
A flows out of the V
REF
COM
terminal, therefore, it is recommended that it be connected
through a low impedance path to sensor common to avoid
possible ground loop problems.
Reference noise is proportional to the reference voltage
selected. With V
REF
= 2.5V, 0.1Hz to 10Hz peak-to-peak
noise is approximately 9
μ
Vp-p. Noise increases to 36
μ
Vp-p
for the 10V reference. Output drive capability of the voltage
reference is improved by connecting a transistor as shown in
Figure 4. The external transistor also serves to remove power
from the INA125.
Internal resistors that set the voltage reference output are
ratio-trimmed for accurate output voltages (
±
0.5% max). The
absolute resistance values, however, may vary
±
25%. Adjust-
ment of the reference output voltage with an external resistor
is not recommended because the required resistor value is
uncertain.
SHUTDOWN
The INA125 has a shutdown option. When the SLEEP pin
is LOW (100mV or less), the supply current drops to
approximately 1
μ
A and output impedance becomes approxi-
mately 80k
. Best performance is achieved with CMOS
logic. To maintain low sleep current at high temperatures,
V
SLEEP
should be as close to 0V as possible. This should not
be a problem if using CMOS logic unless the CMOS gate is
driving other currents. Refer to the typical performance
curve, “Sleep Current vs Temperature.”
A transition region exists when V
SLEEP
is between 400mV
and 2.7V (with respect to V
REF
COM) where the output is
unpredictable. Operation in this region is not recommended.
The INA125 achieves high accuracy quickly following wake-
up (V
SLEEP
≥
2.7V). See the typical performance curve
“Input-Referred Offset Voltage vs Sleep Turn-on Time.” If
shutdown is not being used, connect the SLEEP pin to V+.
LOW VOLTAGE OPERATION
The INA125 can be operated on power supplies as low as
±
1.35V. Performance remains excellent with power sup-
plies ranging from
±
1.35V to
±
18V. Most parameters vary
only slightly throughout this supply voltage range—see
typical performance curves. Operation at very low supply
voltage requires careful attention to ensure that the com-
mon-mode voltage remains within its linear range. See
“Input Common-Mode Voltage Range.” As previously men-
tioned, when using the on-board reference with low supply
voltages, it may be necessary to connect V
REF
COM to V– to
ensure V
S
– V
REF
≥
1.25V.
SINGLE SUPPLY OPERATION
The INA125 can be used on single power supplies of +2.7V
to +36V. Figure 5 shows a basic single supply circuit. The
IA
REF
, V
REF
COM, and V– terminals are connected to ground.
Zero differential input voltage will demand an output volt-
age of 0V (ground). When the load is referred to ground as
shown, actual output voltage swing is limited to approxi-
mately 150mV above ground. The typical performance curve
“Output Voltage Swing vs Output Current” shows how the
output swing varies with output current.
With single supply operation, careful attention should be
paid to input common-mode range, output voltage swing of
both op amps, and the voltage applied to the IA
REF
terminal.
V
IN+
and V
IN–
must both be 1V above ground for linear
operation. You cannot, for instance, connect the inverting
input to ground and measure a voltage connected to the non-
inverting input.
FIGURE 5. Single Supply Bridge Amplifier.
1000
+3V
R
L
1.5V –
V
1.5V +
V
+3V
R
G
INA125
V
O
3
5
12
Ref
Amp
to load
(transducer)
V+
Bandgap
V
REF
13
12
14
15
16
4
INA125
V
REF
COM
V
REF
BG
V
REF
2.5
V
REF
5
V
REF
10
V
REF
Out
TIP29C
10V
FIGURE 4. Reference Current Boost.