Datasheet

10kW
OPA177
100W
100W
1/2 REF200
1/2 REF200
V+
R
G
INA129
Ref
V
O
V
IN
V
IN
+
10mV±
Adjustment Range
V-
100 Am
100 Am
-
INA129-EP
www.ti.com SBOS508 –DECEMBER 2009
Noise Performance
The INA129 provides very low noise in most applications. Low frequency noise is approximately 0.2 μVPP
measured from 0.1 Hz to 10 Hz (G ≥ 100). This provides dramatically improved noise when compared to
state-of-the-art chopper-stabilized amplifiers.
Offset Trimming
The INA129 is laser trimmed for low offset voltage and offset voltage drift. Most applications require no external
offset adjustment. Figure 24 shows an optional circuit for trimming the output offset voltage. The voltage applied
to Ref terminal is summed with the output. The operational amplifier buffer provides low impedance at the Ref
terminal to preserve good common-mode rejection.
Figure 24. Optional Trimming of Output Offset Voltage
Input Bias Current Return Path
The input impedance of the INA129 is extremely high (approximately 10
10
Ω). However, a path must be provided
for the input bias current of both inputs. This input bias current is approximately ±2 nA. High input impedance
means that this input bias current changes very little with varying input voltage.
Input circuitry must provide a path for this input bias current for proper operation. Figure 25 shows various
provisions for an input bias current path. Without a bias current path, the inputs will float to a potential which
exceeds the common-mode range, and the input amplifiers will saturate.
If the differential source resistance is low, the bias current return path can be connected to one input (see the
thermocouple example in Figure 25). With higher source impedance, using two equal resistors provides a
balanced input with possible advantages of lower input offset voltage due to bias current and better
high-frequency common-mode rejection.
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Product Folder Link(s): INA129-EP