LM221资料

TL H 7769LM221 LM321Precision Preamplifiers
February 1995
LM221 LM321Precision Preamplifiers
General Description
The LM221series are precision preamplifiers designed to operate with general purpose operational amplifiers to dras-tically decrease dc errors Drift bias current common mode and supply rejection are more than a factor of 50better than standard op amps alone Further the added dc gain of the LM221decreases the closed loop gain error
The LM221series operates with supply voltages from g 3V to g 20V and has sufficient supply rejection to operate from unregulated supplies The operating current is programma-ble from 5m A to 200m A 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 LM221will improve accuracy on almost any precision dc circuit For example instrumen-tation amplifier strain gauge amplifiers and thermocouple amplifiers now using chopper amplifiers can be made with
the LM221 The full differential input and high common-mode 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 LM221allows tailoring the input characteris-tics to match those of specialized op amps
The LM221is specified over a b 25 C to a 85 C range and the LM321over a 0 C to a 70 C temperature range
Features
Y Guaranteed drift of LM321A 0 2m V C Y Guaranteed drift of LM221series 1m V C Y Offset voltage less than 0 4mV
Y Bias current less than 10nA at 10m A operating current Y CMRR 126dB minimum Y 120dB supply rejection Y
Easily nulled offset voltage
Typical Applications
Thermocouple Amplifier with Cold Junction Compensation
TL H 7769–1
Set for 2 98V at output with LM113shorted Output should equal ambi-ent temperature at 10mV K
Adjust for output reading in C
C 1995National Semiconductor Corporation RRD-B30M115 Printed in U S A
Absolute Maximum Ratings
Supply Voltage g20V Power Dissipation(Note1)500mW Differential Input Voltage(Notes2and3)g15V Input Voltage(Note3)g15V Operating Temperature Range
LM321A0 C to a70 C Storage Temperature Range b65 C to a150 C Lead Temperature(Soldering 10sec )300 C ESD rating to be determined
Electrical Characteristics(Note4)LM321A
Parameter Conditions
LM321A
Units Min Typ Max
Input Offset Voltage T A e25 C 6 4k s R SET s70k0 20 4mV Input Offset Current T A e25 C
R SET e70k0 30 5nA
R SET e6 4k5nA
Input Bias Current T A e25 C
R SET e70k515nA
R SET e6 4k50150nA Input Resistance T A e25 C
R SET e70k28M X
R SET e6 4k0 2M X Supply Current T A e25 C R SET e70k0 82 2mA Input Offset Voltage6 4k s R SET s70k0 50 65mV
Input Bias Current R SET e70k1525nA
R SET e6 4k150250nA
Input Offset Current R SET e70k0 51nA
R SET e6 4k510nA Input Offset Current Drift R SET e70k3pA C Average Temperature R S s200X 6 4k s R SET s70k
Coefficient of Input Offset Offset Voltage Nulled
Voltage0 070 2m V C
Long Term Stability3m V yr Supply Current13 5mA
Input Voltage Range V S e g15V (Note5)
R SET e70k g13V
R SET e6 4k a7 b13V
Common-Mode Rejection R SET e70k126140dB Ratio R SET e6 4k120130dB
Supply Voltage Rejection R SET e70k118126dB Ratio R SET e6 4k114120dB
Voltage Gain T A e25 C R SET e70k
R L l3M X1220V V Noise R SET e70k R SOURCE e08nV 0Hz Note1 The maximum junction temperature of the LM321A is85 C For operating at elevated temperature devices in the H08package must be derated based on a thermal resistance of150 C W junction to ambient or18 C W junction to case
Note2 The inputs are shunted with back-to-back diodes in series with a500X resistor for overvoltage protection Therefore excessive current will flow if a differential input voltage in excess of1V is applied between the inputs
Note3 For supply voltages less than g15V the absolute maximum input voltage is equal to the supply voltage
Note4 These specifications apply for g5s V S s g20V and b55 C s T A s a125 C unless otherwise specified With the LM221A however all temperature specifications are limited to b25 C s T A s a85 C and for the LM321A the specifications apply over a0 C to a70 C temperature range
Note5 External precision resistor 0 1% can be placed from pins1and8to7increase positive common-mode range
Note6 See RETS121X for LM121H 883military specs and RET121AX for LM121AH 883military specs
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 g20V Power Dissipation(Note1)500mW Differential Input Voltage(Notes2and3)g15V Input Voltage(Note3)g15V Operating Temperature Range
LM221 LM121A(-883) LM121(-883)b25 C to a85 C LM321 LM321A0 C to a70 C Storage Temperature Range b65 C to a150 C Lead Temperature(Soldering 10sec )260 C ESD rating to be determined
Electrical Characteristics(Note4)LM221 LM321
Parameter Conditions
LM221LM321
Units Min Typ Max Min Typ Max
Input Offset Voltage T A e25 C 6 4k s R SET s70k0 71 5mV Input Offset Current T A e25 C
R SET e70k12nA
R SET e6 4k1020nA
Input Bias Current T A e25 C
R SET e70k1018nA
R SET e6 4k100180nA Input Resistance T A e25 C
R SET e70k42M X
R SET e6 4k0 40 2M X Supply Current T A e25 C R SET e70k1 52 2mA Input Offset Voltage6 4k s R SET s70k1 02 5mV
Input Bias Current R SET e70k3028nA R SET e6 4k300280nA
Input Offset Current R SET e70k34nA R SET e6 4k3040nA
Input Offset Current Drift R SET e70k33pA C
Average Temperature R S s200X 6 4k s R SET s70k
Coefficient of Input Offset Voltage Nulled11m V C Offset Voltage
Long Term Stability55m V yr Supply Current2 53 5mA
Input Voltage Range V S e g15V (Note5)
R SET e70k g13g13V
R SET e6 4k a7 b13a7 b13V
Common-Mode Rejection R SET e70k120114dB Ratio R SET e6 4k114114dB
Supply Voltage Rejection R SET e70k120114dB Ratio R SET e6 4k114114dB
Voltage Gain T A e25 C R SET e70k
R L l3M X1612V V Noise R SET e70k R SOURCE e088nV 0Hz Note1 The maximum junction temperature of the LM221is100 C The maximum junction temperature of the LM321is85 C For operating at elevated temperature devices in the H08package must be derated based on a thermal resistance of150 C W junction to ambient or18 C W junction to case
Note2 The inputs are shunted with back-to-back diodes in series with a500X resistor for overvoltage protection Therefore excessive current will flow if a differential input voltage in excess of1V is applied between the inputs
Note3 For supply voltages less than g15V the absolute maximum input voltage is equal to the supply voltage
Note4 These specifications apply for g5s V S s g20V and b55 C s T A s a125 C unless otherwise specified With the LM221 however all temperature specifications are limited to b25 C s T A s a85 C and for the LM321the specifications apply over a0 C to a70 C temperature range
Note5 External precision resistor 0 1% can be placed from pins1and8to7increase positive common-mode range
3
Typical Performance Characteristics
Input Bias Current
Voltage Drift (Nulled)
Distribution of Offset Voltage Drift (Nulled)
Distribution of Offset Rejection Positive Power Supply Rejection
Negative Power Supply Input Noise Voltage
Input Noise Current Voltage Drift Differential Voltage Gain
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
Common-Mode Rejection Supply Current Offset Voltage Adjustment Ratio
TL H 7769–10
Connection Diagram
Metal Can Package
TL H 7769–7
Top View
Note Pin4connected to case
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
5
Schematic Diagram
T L H 7769–8
6
Frequency Compensation
UNIVERSAL COMPENSATION
The additional gain of the LM321preamplifier when used with an operational amplifier usually necessitates additional frequency compensation When the closed loop gain of the op amp with the LM321is less than the gain of the LM321 alone more compensation is needed The worst case situa-tion is when there is100%feedback such as a voltage follower or integrator and the gain of the LM321is high When high closed loop gains are used for example A V e 1000 and only an addition gain of200is inserted by the LM321 the frequency compensation of the op amp will usu-ally suffice
The frequency compensation shown here is designed to op-erate with any unity-gain stable op amp Figure1shows the basic configuration of frequency stabilizing network In oper-ation the output of the LM321is rendered single ended by a 0 01m F bypass capacitor to ground Overall frequency com-pensation then is achieved by an integrating capacitor around the op amp
Bandwidth at unity-gain j
12
2q R SET C
for0 5MHz bandwidth C e
4 106R SET
For use with higher frequency op amps such as the LM118 the bandwidth may be increased to about2MHz
If the closed loop gain is greater than unity ‘‘C’’may be decreased to
C e
4
106A CL R 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
C e
8
106A CL R SET
Table I shows typical values for the two compensating ca-
pacitors for various gains and operating currents
TABLE I
Closed Current Set Resistor
Loop
Gain120k X60k X30k X12k X6k X
A V e1681302706801300
A V e5152756130270
A V e1010152768130
A V e501351527
A V e100–13510
A V e500––113
A V e1000–––––
This table applies for the LM108 LM101A LM741 LM118
Capacitance is in pF
DESIGN EQUATIONS FOR THE LM321SERIES
Gain A V
1 2c106
R SET
Null Pot Value should be10%of R SET
Operating Current
2c0 65V
R SET
Positive Common-Mode Limit V a b 0 6b0 65V c50k
R SET(
Typical Applications
Offset adjust
See table for frequency compensation
TL H 7769–2
FIGURE1 Low Drift Op Amp Using the LM321A as a Preamp
7
Typical Applications(Continued)
Gain of1000Instrumentation Amplifier
Offset adjust
Gain trim
Better than1%linearity for input sig-
nals up to g10mV gain stability typi-
cal a2%from b55to a125 C
Match of R5and R6effect power
supply rejection
TL H 7769–3
High Speed Inverting Amplifier with Low Drift
Bandwidth e10MHz
Slew Rate e40V m s
TL H 7769–4
Medium Speed General Purpose Amplifier
Bandwidth e3 5MHz
Slew Rate e1 1V m s
TL H 7769–5
8
Typical Applications(Continued)
Increased Common-Mode Range at High Operating Currents
Match to0 1%
Depends on close loop gain
TL H 7769–6
9
L M 221 L M 321P r e c i s i o n P r e a m p l i f i e r s
Physical Dimensions inches (millimeters)
Metal Can Package (H)
Order Number LM221H LM321H or LM321AH
NS Package Number H08C
LIFE SUPPORT POLICY
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 1 Life support devices or systems are devices or 2 A critical component is any component of a life 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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