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

-

INA128-HT, INA129-HT

SBOS501D – JANUARY 2010 – REVISED JUNE 2012

www.ti.com

Dynamic Performance

Figure 2 shows that, despite its low quiescent current, the INA128/INA129 achieves wide bandwidth, even at

high gain. This is due to the current-feedback topology of the input stage circuitry. Settling time also remains

excellent at high gain.

Noise Performance

The INA128/INA129 provides very low noise in most applications. Low frequency noise is approximately 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 INA128/INA129 is laser trimmed for low offset voltage and offset voltage drift. Most applications require no

external offset adjustment. Figure 25 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.

(1)

OPA177 and REF200 are not tested or characterized at 210°C.

Figure 25. 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 ±50 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 26 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 26). 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.

16

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