INA128
INA129
www.ti.com
SBOS051B − OCTOBER 1995 − REVISED FEBRUARY 2005
Operation at very low supply voltage requires careful
attention to assure that the input voltages remain within
their linear range. Voltage swing requirements of
internal nodes limit the input common-mode range with
low power supply voltage. Typical performance curves,
“Input Common-Mode Range vs Output Voltage” show
the range of linear operation for
±15V, ±5V,
and
±2.5V
supplies.
K
V+
10.0V
6
REF102
R
1
R
2
4
Pt100
Cu
2
+5V
2.5V −
∆V
R
G
2.5V +
∆V
INA128
Ref
V
O
Cu
R
G
R3
100Ω = Pt100 at 0°C
INA128
Ref
V
O
300Ω
ISA
TYPE
E
J
MATERIAL
+ Chromel
− Constantan
+ Iron
− Constantan
+ Chromel
− Alumel
+ Copper
− Constantan
SEEBECK
COEFFICIENT
(µV/5C)
58.5
50.2
39.4
38.0
R
1
, R
2
66.5kΩ
76.8kΩ
97.6kΩ
102kΩ
Figure 4. Bridge Amplifier
K
T
−
V
IN
+
R
G
INA128
Ref
C1
0.1µF
V
O
Figure 6. Thermocouple Amplifier with RTD
Cold-Junction Compensation
−
V
IN
+
Ref
R
G
INA128
I
B
A
1
A
1
OPA177
OPA131
OPA602
OPA128
I
B
ERROR
±
1.5nA
±
50pA
±
1pA
±
75fA
R
1
1MΩ
R
1
I
O
+
V
IN
@
G
R
1
OPA130
1
=
f−3dB
2πR
1
C
1
= 1.59Hz
I
O
Load
Figure 5. AC-Coupled Instrumentation Amplifier
Figure 7. Differential Voltage to Current Converter
R
G
= 5.6kΩ
2.8kΩ
G = 10
RA
LA
R
G
/2
2.8kΩ
390kΩ
RL
390kΩ
1/2
OPA2131
INA128
Ref
V
O
V
G
10kΩ
V
G
1/2
OPA2131
NOTE: Due to the INA128’s current-feedback
topology, VG is approximately 0.7V less than
the common-mode input voltage. This DC offset
in this guard potential is satisfactory for many
guarding applications.
Figure 8. ECG Amplifier with Right-Leg Drive
11
TI [ TEXAS INSTRUMENTS ]
