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 A

m

100 A

m

-

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

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.

Copyright © 2009, Texas Instruments Incorporated

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Product Folder Link(s): INA129-EP