National Semiconductor LM221 LM321 Precision Preamplifiers Data Sheet User Manual

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LM221/LM321 Precision Preamplifiers General Description

The LM221 series are precision preamplifiers designed to the LM221. The full differential input and high common- operate with general purpose operational amplifiers to dras- mode rejection are another advantage over choppers. For tically decrease dc errors. Drift, bias current, common mode applications where low bias current is more important than and supply rejection are more than factor of better than drift, the operating current can be reduced to low values. standard op amps alone. Further, the added dc gain of the High operating currents can be used for low voltage noise LM221 decreases the closed loop gain error. with low source resistance. The programmable operating g3V current of the LM221 allows tailoring the input characteris-

The LM221 series operates with supply voltages from

g20V tics to match those of specialized op amps.

to and has sufficient supply rejection to operate from

unregulated supplies. The operating current is programma- The LM221 is specified over b25§C to a85§C range and ble from m A to m A so bias current, offset current, gain the LM321 over 0§C to a70§C temperature range.

and noise can be optimized for the particular application while still realizing very low drift. Super-gain transistors are Features used for the input stage so input error currents are lower

Guaranteed drift of LM321AÐ0.2 m V/§C

than conventional amplifiers at the same operating current.

Guaranteed drift of LM221 seriesÐ1 m V/§C

Further, the initial offset voltage is easily nulled to zero.

Offset voltage less than 0.4 m V

The extremely low drift of the LM221 will improve accuracy

Bias current less than n A at m A operating current

on almost any precision dc circuit. For example, instrumen-

CMRR d B minimum

tation amplifier, strain gauge amplifiers and thermocouple

d B supply rejection

amplifiers now using chopper amplifiers can be made with

Easily nulled offset voltage

Typical Applications

Thermocouple Amplifier with Cold Junction Compensation

*Set for 2.98V at output with LM113 shorted. Output should equal ambi- ent temperature at m V/§K. ²Adjust for output reading in §C.

TL/H/7769–1

C1995 National Semiconductor Corporation TL/H/7769 RRD-B30M115/Printed in U. S. A.