National Semiconductor LM221, LM321 Technical data

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LM221/LM321 Precision Preamplifiers

General Description

The LM221 series are precision preamplifiers designed to
operate with general purpose operational amplifiers to dras­tically decrease dc errors. Drift, bias current, common mode
and supply rejection are more than a factor of 50 better than
standard op amps alone. Further, the added dc gain of the
LM221 decreases the closed loop gain error.

The LM221 series operates with supply voltages from

g

to

20V and has sufficient supply rejection to operate from
unregulated supplies. The operating current is programma­ble from 5 m Ato200mA so bias current, offset current, gain
and noise can be optimized for the particular application
while still realizing very low drift. Super-gain transistors are
used for the input stage so input error currents are lower
than conventional amplifiers at the same operating current.
Further, the initial offset voltage is easily nulled to zero.

The extremely low drift of the LM221 will improve accuracy
on almost any precision dc circuit. For example, instrumen­tation amplifier, strain gauge amplifiers and thermocouple
amplifiers now using chopper amplifiers can be made with

the LM221. The full differential input and high common­mode rejection are another advantage over choppers. For
applications where low bias current is more important than
drift, the operating current can be reduced to low values.
High operating currents can be used for low voltage noise
with low source resistance. The programmable operating
current of the LM221 allows tailoring the input characteris-

g

3V

tics to match those of specialized op amps.

The LM221 is specified over a
the LM321 over a 0

Ctoa70§C temperature range.

§

b

25§Ctoa85§C range and

Features

Y

Guaranteed drift of LM321AÐ0.2 mV/§C

Y

Guaranteed drift of LM221 seriesÐ1 mV/§C

Y

Offset voltage less than 0.4 mV

Y

Bias current less than 10 nA at 10 mA operating current

Y

CMRR 126 dB minimum

Y

120 dB supply rejection

Y

Easily nulled offset voltage

LM221/LM321 Precision Preamplifiers

February 1995

Typical Applications

Thermocouple Amplifier with Cold Junction Compensation

*Set for 2.98V at output with LM113

shorted. Output should equal ambi­ent temperature at 10 mV/

²

Adjust for output reading in§C.

K.

§

TL/H/7769– 1

C

1995 National Semiconductor Corporation RRD-B30M115/Printed in U. S. A.

TL/H/7769

Absolute Maximum Ratings

Supply Voltage

Power Dissipation (Note 1) 500 mW

Differential Input Voltage (Notes 2 and 3)

Input Voltage (Note 3)

g

20V

g

15V

g

15V

Operating Temperature Range

LM321A 0

Storage Temperature Range

Ctoa70§C

§

b

65§Ctoa150§C

Lead Temperature (Soldering, 10 sec.) 300

ESD rating to be determined.

Electrical Characteristics (Note 4) LM321A

Parameter Conditions

Input Offset Voltage T

Input Offset Current T

Input Bias Current T

Input Resistance T

Supply Current T

e

25§C, 6.4ksR

A

e

25§C,

A

R

SET

R

SET

e

25§C,

A

R

SET

R

SET

e

25§C,

A

R

SET

R

SET

e

25§C, R

A

Input Offset Voltage 6.4ksR

Input Bias Current R

Input Offset Current R

Input Offset Current Drift R

Average Temperature R

e

SET

e

R

SET

e

SET

e

R

SET

e

SET

s

200X, 6.4ksR

S

s

70k 0.2 0.4 mV

SET

e

70k 0.3 0.5 nA

e

6.4k 5 nA

e

70k 5 15 nA

e

6.4k 50 150 nA

e

70k 2 8 MX

e

6.4k 0.2 MX

e

70k 0.8 2.2 mA

SET

s

70k 0.5 0.65 mV

SET

70k 15 25 nA

6.4k 150 250 nA

70k 0.5 1 nA

6.4k 5 10 nA

70k 3 pA/§C

s

70k

SET

Min Typ Max

Coefficient of Input Offset Offset Voltage Nulled
Voltage 0.07 0.2 mV/

Long Term Stability 3 mV/yr

Supply Current 1 3.5 mA

e

Input Voltage Range V

Common-Mode Rejection R
Ratio R

Supply Voltage Rejection R
Ratio R

Voltage Gain T

Noise R

Note 1: The maximum junction temperature of the LM321A is 85§C. For operating at elevated temperature, devices in the H08 package must be derated based on
a thermal resistance of 150

Note 2: The inputs are shunted with back-to-back diodes in series with a 500X resistor for overvoltage protection. Therefore, excessive current will flow if a
differential input voltage in excess of 1V is applied between the inputs.

Note 3: For supply voltages less than

Note 4: These specifications apply for

specifications are limited to

Note 5: External precision resistor Ð0.1%Ð can be placed from pins 1 and 8 to 7 increase positive common-mode range.

Note 6: See RETS121X for LM121H/883 military specs and RET121AX for LM121AH/883 military specs.

C/W, junction to ambient, or 18§C/W, junction to case.

§

g

g

b

25§CsT

g

15V, (Note 5)

S

e

R

70k

SET

e

R

6.4k

SET

e

70k 126 140 dB

SET

e

6.4k 120 130 dB

SET

e

70k 118 126 dB

SET

e

6.4k 114 120 dB

SET

e

25§C, R

A

l

R

3MX 12 20 V/V

L

e

SET

15V, the absolute maximum input voltage is equal to the supply voltage.

s

g

5sV

A

s

20V andb55§CsT

S

a

85§C, and for the LM321A the specifications apply over a 0§Ctoa70§C temperature range.

70k, R

SET

SOURCE

e

70k,

e

0 8 nV/0Hz

s

a

125§C, unless otherwise specified. With the LM221A, however all temperature

A

g

a7,b

LM321A

Units

13 V

13 V

C

§

C

§

2

Absolute Maximum Ratings

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.

Supply Voltage

g

20V

Power Dissipation (Note 1) 500 mW

g

Differential Input Voltage (Notes 2 and 3)

Input Voltage (Note 3)

15V

g

15V

Operating Temperature Range

LM221, LM121A (-883), LM121 (-883)
LM321, LM321A 0

Storage Temperature Range

b

25§Ctoa85§C

Ctoa70§C

§

b

65§Ctoa150§C

Lead Temperature (Soldering, 10 sec.) 260§C

ESD rating to be determined.

Electrical Characteristics (Note 4) LM221, LM321

Parameter Conditions

Input Offset Voltage T

Input Offset Current T

Input Bias Current T

Input Resistance T

Supply Current T

Input Offset Voltage 6.4ksR

Input Bias Current R

Input Offset Current R

Input Offset Current Drift R

Average Temperature R
Coefficient of Input Offset Voltage Nulled 1 1 mV/

e

25§C, 6.4ksR

A

e

25§C,

A

e

R

70k 1 2 nA

SET

e

R

6.4k 10 20 nA

SET

e

25§C,

A

e

R

70k 10 18 nA

SET

e

R

6.4k 100 180 nA

SET

e

25§C,

A

e

R

70k 4 2 MX

SET

e

R

6.4k 0.4 0.2 MX

SET

e

25§C, R

A

SET

R

SET

SET

R

SET

SET

s

S

SET

s

70k 1.0 2.5 mV

SET

e

70k 30 28 nA

e

6.4k 300 280 nA

e

70k 3 4 nA

e

6.4k 30 40 nA

e

70k 3 3 pA/§C

200X, 6.4ksR

s

70k 0.7 1.5 mV

SET

e

70k 1.5 2.2 mA

s

70k

SET

Offset Voltage

Long Term Stability 5 5 mV/yr

Supply Current 2.5 3.5 mA

e

Input Voltage Range V

Common-Mode Rejection R
Ratio R

Supply Voltage Rejection R
Ratio R

Voltage Gain T

Noise R

Note 1: The maximum junction temperature of the LM221 is 100§C. The maximum junction temperature of the LM321 is 85§C. For operating at elevated
temperature, devices in the H08 package must be derated based on a thermal resistance of 150

Note 2: The inputs are shunted with back-to-back diodes in series with a 500X resistor for overvoltage protection. Therefore, excessive current will flow if a
differential input voltage in excess of 1V is applied between the inputs.

Note 3: For supply voltages less than

Note 4: These specifications apply for

specifications are limited to

Note 5: External precision resistor Ð0.1%Ð can be placed from pins 1 and 8 to 7 increase positive common-mode range.

b

25§CsT

g

15V, (Note 5)

S

e

R

70k

SET

e

R

6.4k

SET

e

70k 120 114 dB

SET

e

6.4k 114 114 dB

SET

e

70k 120 114 dB

SET

e

6.4k 114 114 dB

SET

e

25§C, R

A

l

R

3MX 16 12 V/V

L

e

SET

g

15V, the absolute maximum input voltage is equal to the supply voltage.

g

5sV

s

a

A

e

70k,

SET

70k, R

s

g

S

85§C, and for the LM321 the specifications apply over a 0§Ctoa70§C temperature range.

e

SOURCE

20V andb55§CsT

0 8 8 nV/0Hz

s

A

LM221 LM321

Min Typ Max Min Typ Max

g

13

a7,b

13

C/W, junction to ambient, or 18§C/W, junction to case.

§

a

125§C, unless otherwise specified. With the LM221, however all temperature

g

13 V

a7,b

13 V

Units

C

§

3

Typical Performance Characteristics

Input Bias Current Voltage Drift (Nulled)

Positive Power Supply
Rejection

Input Noise Current Voltage Drift Differential Voltage Gain

Distribution of Offset

Negative Power Supply
Rejection

Distribution of Offset
Voltage Drift (Nulled)

Input Noise Voltage

Set Resistor and Set Current Set Current Common-Mode Limits

TL/H/7769– 9

4

Typical Performance Characteristics (Continued)

Common-Mode Limits Output Common-Mode Voltage Differential Voltage Gain

Supply Current Offset Voltage Adjustment Ratio

Connection Diagram

Order Number LM121AH/883, LM121H/883,

LM221H, LM321H or LM321AH

See NS Package Number H08C

Note: Outputs are inverting from the input of the same number.

Common-Mode Rejection

TL/H/7769– 10

Metal Can Package

TL/H/7769– 7

Top View

Note: Pin 4 connected to case.

5

Schematic Diagram

TL/H/7769– 8

6

Frequency Compensation

UNIVERSAL COMPENSATION

The additional gain of the LM321 preamplifier when used
with an operational amplifier usually necessitates additional
frequency compensation. When the closed loop gain of the
op amp with the LM321 is less than the gain of the LM321
alone, more compensation is needed. The worst case situa­tion is when there is 100% feedbackÐsuch as a voltage
follower or integratorÐand the gain of the LM321 is high.
When high closed loop gains are usedÐfor example A
1000Ðand only an addition gain of 200 is inserted by the
LM321, the frequency compensation of the op amp will usu­ally suffice.

The frequency compensation shown here is designed to op­erate with any unity-gain stable op amp.

Figure 1

basic configuration of frequency stabilizing network. In oper­ation the output of the LM321 is rendered single ended by a

0.01 mF bypass capacitor to ground. Overall frequency com­pensation then is achieved by an integrating capacitor
around the op amp.

12

Bandwidth at unity-gain

for 0.5 MHz bandwidth C

j

2qR

C

SET

4

e

106R

SET

For use with higher frequency op amps such as the LM118
the bandwidth may be increased to about 2 MHz.

If the closed loop gain is greater than unity, ‘‘C’’ may be
decreased to:

4

e

C

106ACLR

SET

ALTERNATE COMPENSATION

The two compensation capacitors can be made equal for
improved power supply rejection. In this case the formula for
the compensation capscitor is:

8

e

C

106ACLR

SET

V

shows the

Table I shows typical values for the two compensating ca­pacitors for various gains and operating currents.

TABLE I

Closed

Loop

Gain

e

A

V

A

V

A

V

A

V

e

A

V

e

A

V

e

A

V

120 kX 60 kX 30 kX 12 kX 6kX

e

1 68 130 270 680 1300

e

5 15 27 56 130 270

e

10 10 15 27 68 130

e

50 1 3 5 15 27
100 – 1 3 5 10
500 – – 1 1 3

1000 – – – – –

Current Set Resistor

This table applies for the LM108, LM101A, LM741, LM118.
Capacitance is in pF.

DESIGN EQUATIONS FOR THE LM321 SERIES

6

c

10

1.2

&

Gain A

V

R

Null Pot Value should be 10% of R

Operating Current

Positive Common-Mode Limit&V

SET

SET

c

2

0.65V

&

R

SET

0.6

Ð

0.65Vc50k

b

R

SET

(

a

b

Typical Applications

*Offset adjust.

²

See table for frequency compensation.

FIGURE 1. Low Drift Op Amp Using the LM321A as a Preamp

TL/H/7769– 2

7

Typical Applications (Continued)

Gain of 1000 Instrumentation Amplifier

High Speed* Inverting Amplifier with Low Drift

³

*Offset adjust

²

Gain trim

³

Better than 1% linearity for input sig-

g

nals up to
cal

Match of R5 and R6 effect power
supply rejection

10 mV gain stability typi-

a

2% fromb55 toa125§C.

TL/H/7769– 3

Medium Speed* General Purpose Amplifier

8

*Bandwidthe10 MHz

*Bandwidthe3.5 MHz

Slew Rate

Slew Rate

TL/H/7769– 5

e

40 V/ms

TL/H/7769– 4

e

1.1 V/ms

Typical Applications (Continued)

Increased Common-Mode Range at High Operating Currents

*Match to 0.1%

²

Depends on close loop gain

TL/H/7769– 6

9

Physical Dimensions inches (millimeters)

LM221/LM321 Precision Preamplifiers

Order Number LM221H, LM321H or LM321AH

Metal Can Package (H)

NS Package Number H08C

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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL
SEMICONDUCTOR CORPORATION. As used herein:

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systems which, (a) are intended for surgical implant support device or system whose failure to perform can
into the body, or (b) support or sustain life, and whose be reasonably expected to cause the failure of the life
failure to perform, when properly used in accordance support device or system, or to affect its safety or
with instructions for use provided in the labeling, can effectiveness.
be reasonably expected to result in a significant injury
to the user.

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a

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