NSC LF256 Jfet input operational amplifier Datasheet

LF155/LF156/LF256/LF257/LF355/LF356/LF357
JFET Input Operational Amplifiers
General Description
These are the first monolithic JFET input operational amplifiers to incorporate well matched, high voltage JFETs on the
same chip with standard bipolar transistors (BI-FET™ Technology). These amplifiers feature low input bias and offset
currents/low offset voltage and offset voltage drift, coupled
with offset adjust which does not degrade drift or
common-mode rejection. The devices are also designed for
high slew rate, wide bandwidth, extremely fast settling time,
low voltage and current noise and a low 1/f noise corner.
Features
Advantages
n Replace expensive hybrid and module FET op amps
n Rugged JFETs allow blow-out free handling compared
with MOSFET input devices
n Excellent for low noise applications using either high or
low source impedance — very low 1/f corner
n Offset adjust does not degrade drift or common-mode
rejection as in most monolithic amplifiers
n New output stage allows use of large capacitive loads
(5,000 pF) without stability problems
n Internal compensation and large differential input voltage
capability
Common Features
n Low input bias current: 30pA
n Low Input Offset Current: 3pA
n High input impedance: 1012Ω
n Low input noise current:
n High common-mode rejection ratio:
n Large dc voltage gain: 106 dB
100 dB
Uncommon Features
j Extremely
LF155/
LF355
LF156/
LF256/
LF356
LF257/
LF357
(AV =5)
Units
4
1.5
1.5
µs
5
12
50
V/µs
2.5
5
20
MHz
20
12
12
fast settling
time to
0.01%
j Fast slew
rate
j Wide gain
bandwidth
Applications
n
n
n
n
n Logarithmic amplifiers
n Photocell amplifiers
n Sample and Hold circuits
Precision high speed integrators
Fast D/A and A/D converters
High impedance buffers
Wideband, low noise, low drift amplifiers
j Low input
noise
voltage
Simplified Schematic
00564601
*3pF in LF357 series.
BI-FET™, BI-FET II™ are trademarks of National Semiconductor Corporation.
© 2001 National Semiconductor Corporation
DS005646
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LF155/LF156/LF256/LF257/LF355/LF356/LF357 JFET Input Operational Amplifiers
December 2001
LF155/LF156/LF256/LF257/LF355/LF356/LF357
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required, contact the National Semiconductor Sales Office/Distributors for
availability and specifications.
LF155/6
LF256/7/LF356B
LF355/6/7
Input Voltage Range (Note 2)
± 22V
± 40V
± 20V
± 22V
± 40V
± 20V
± 18V
± 30V
± 16V
Output Short Circuit Duration
Continuous
Continuous
Continuous
Supply Voltage
Differential Input Voltage
TJMAX
H-Package
115˚C
115˚C
N-Package
150˚C
100˚C
100˚C
M-Package
100˚C
100˚C
Power Dissipation at TA = 25˚C (Notes
1, 8)
H-Package (Still Air)
560 mW
400 mW
400 mW
H-Package (400 LF/Min Air Flow)
1200 mW
1000 mW
1000 mW
N-Package
670 mW
670 mW
M-Package
380 mW
380 mW
160˚C/W
160˚C/W
160˚C/W
65˚C/W
65˚C/W
65˚C/W
N-Package
130˚C/W
130˚C/W
M-Package
195˚C/W
195˚C/W
Thermal Resistance (Typical) θJA
H-Package (Still Air)
H-Package (400 LF/Min Air Flow)
(Typical) θJC
H-Package
Storage Temperature Range
23˚C/W
23˚C/W
23˚C/W
−65˚C to +150˚C
−65˚C to +150˚C
−65˚C to +150˚C
300˚C
300˚C
300˚C
260˚C
260˚C
260˚C
Soldering Information (Lead Temp.)
Metal Can Package
Soldering (10 sec.)
Dual-In-Line Package
Soldering (10 sec.)
Small Outline Package
Vapor Phase (60 sec.)
215˚C
215˚C
Infrared (15 sec.)
220˚C
220˚C
See AN-450 “Surface Mounting Methods and Their Effect on Product Reliability” for other methods of
soldering surface mount devices.
ESD tolerance
(100 pF discharged through 1.5kΩ)
1000V
1000V
1000V
DC Electrical Characteristics
(Note 3)
Symbol
Parameter
Min
VOS
Input Offset Voltage
RS =50Ω, TA =25˚C
Typ
3
Over Temperature
∆VOS/∆T
Average TC of Input
Offset Voltage
RS =50Ω
∆TC/∆VOS
Change in Average TC
with VOS Adjust
RS =50Ω, (Note 4)
IOS
Input Offset Current
Max Min
5
Typ
3
7
TJ =25˚C, (Notes 3, 5)
Max Min
5
Units
Typ
Max
3
10
mV
13
mV
6.5
5
5
µV/˚C
0.5
0.5
0.5
µV/˚C
per mV
20
20
2
LF355/6/7
5
3
TJ≤THIGH
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LF256/7
LF356B
LF155/6
Conditions
3
20
1
3
50
pA
2
nA
(Continued)
(Note 3)
Symbol
Parameter
Min
IB
Input Bias Current
LF256/7
LF356B
LF155/6
Conditions
Typ
TJ =25˚C, (Notes 3, 5)
Max Min
30
100
TJ≤THIGH
Input Resistance
TJ =25˚C
AVOL
Large Signal Voltage
Gain
VS = ± 15V, TA =25˚C
Output Voltage Swing
10
50
Input Common-Mode
Voltage Range
CMRR
Common-Mode
Rejection Ratio
PSRR
Supply Voltage
Rejection Ratio
30
100
Max
30
200
pA
8
nA
5
12
12
50
± 13
± 12
± 12
± 10
Ω
12
10
200
10
200
25
± 13
± 12
± 15.1
± 12
± 10
Units
Typ
200
V/mV
VO = ± 10V, RL =2k
Over Temperature
25
VS = ± 15V, RL =10k
± 12
± 10
VS = ± 15V, RL =2k
VCM
Max Min
50
RIN
VO
Typ
LF355/6/7
VS = ± 15V
± 11
(Note 6)
25
+15.1
± 11
−12
15
+10
−12
V/mV
± 13
± 12
V
+15.1
V
−12
V
V
85
100
85
100
80
100
dB
85
100
85
100
80
100
dB
DC Electrical Characteristics
TA = TJ = 25˚C, VS = ± 15V
Parameter
Supply
Current
LF155
LF355
LF156/256/257/356B
LF356
LF357
Typ
Max
Typ
Max
Typ
Max
Typ
Max
Typ
Max
2
4
2
4
5
7
5
10
5
10
Units
mA
AC Electrical Characteristics
TA = TJ = 25˚C, VS = ± 15V
Symbol
Parameter
LF155/355
LF156/256/
356B
LF156/256/356/
LF356B
LF257/357
Typ
Min
Typ
Typ
5
7.5
12
Conditions
SR
Slew Rate
LF155/6:
AV =1,
GBW
Gain Bandwidth Product
ts
Settling Time to 0.01%
(Note 7)
en
Equivalent Input Noise
Voltage
RS =100Ω
LF357: AV =5
in
CIN
Equivalent Input Current
Noise
Units
V/µs
50
V/µs
2.5
5
20
MHz
4
1.5
1.5
µs
f=100 Hz
25
15
15
f=1000 Hz
20
12
12
f=100 Hz
0.01
0.01
0.01
f=1000 Hz
0.01
0.01
0.01
3
3
3
Input Capacitance
pF
Notes for Electrical Characteristics
Note 1: The maximum power dissipation for these devices must be derated at elevated temperatures and is dictated by TJMAX, θJA, and the ambient temperature,
TA. The maximum available power dissipation at any temperature is PD =(TJMAX−TA)/θJA or the 25˚C PdMAX, whichever is less.
Note 2: Unless otherwise specified the absolute maximum negative input voltage is equal to the negative power supply voltage.
Note 3: Unless otherwise stated, these test conditions apply:
3
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LF155/LF156/LF256/LF257/LF355/LF356/LF357
DC Electrical Characteristics
LF155/LF156/LF256/LF257/LF355/LF356/LF357
Notes for Electrical Characteristics
LF155/156
(Continued)
LF256/257
± 15V ≤ VS ≤ ± 20V
LF356B
± 15V ≤ VS ± 20V
LF355/6/7
Supply Voltage, VS
± 15V ≤ VS ≤ ± 20V
TA
−55˚C ≤ TA ≤ +125˚C
−25˚C ≤ TA ≤ +85˚C
0˚C ≤ TA ≤ +70˚C
0˚C ≤ TA ≤ +70˚C
THIGH
+125˚C
+85˚C
+70˚C
+70˚C
VS = ± 15V
and VOS, IB and IOS are measured at VCM = 0.
Note 4: The Temperature Coefficient of the adjusted input offset voltage changes only a small amount (0.5µV/˚C typically) for each mV of adjustment from its original
unadjusted value. Common-mode rejection and open loop voltage gain are also unaffected by offset adjustment.
Note 5: The input bias currents are junction leakage currents which approximately double for every 10˚C increase in the junction temperature, TJ. Due to limited
production test time, the input bias currents measured are correlated to junction temperature. In normal operation the junction temperature rises above the ambient
temperature as a result of internal power dissipation, Pd. TJ = TA + θJA Pd where θJA is the thermal resistance from junction to ambient. Use of a heat sink is
recommended if input bias current is to be kept to a minimum.
Note 6: Supply Voltage Rejection is measured for both supply magnitudes increasing or decreasing simultaneously, in accordance with common practice.
Note 7: Settling time is defined here, for a unity gain inverter connection using 2 kΩ resistors for the LF155/6. It is the time required for the error voltage (the voltage
at the inverting input pin on the amplifier) to settle to within 0.01% of its final value from the time a 10V step input is applied to the inverter. For the LF357, AV = −5,
the feedback resistor from output to input is 2kΩ and the output step is 10V (See Settling Time Test Circuit).
Note 8: Max. Power Dissipation is defined by the package characteristics. Operating the part near the Max. Power Dissipation may cause the part to operate outside
guaranteed limits.
Typical DC Performance Characteristics
Curves are for LF155 and LF156 unless otherwise
specified.
Input Bias Current
Input Bias Current
00564638
00564637
Input Bias Current
Voltage Swing
00564640
00564639
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4
Curves are for LF155 and LF156 unless otherwise
specified. (Continued)
Supply Current
Supply Current
00564642
00564641
Negative Current Limit
Positive Current Limit
00564643
00564644
Positive Common-Mode
Input Voltage Limit
Negative Common-Mode
Input Voltage Limit
00564645
00564646
5
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LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical DC Performance Characteristics
LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical DC Performance Characteristics
Curves are for LF155 and LF156 unless otherwise
specified. (Continued)
Open Loop Voltage Gain
Output Voltage Swing
00564648
00564647
Typical AC Performance Characteristics
Gain Bandwidth
Gain Bandwidth
00564650
00564649
Normalized Slew Rate
Output Impedance
00564651
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00564652
6
Output Impedance
(Continued)
LF155 Small Signal Pulse Response, AV = +1
00564605
00564653
LF156 Small Signal Pulse Response, AV = +1
LF155 Large Signal Pulse Response, AV = +1
00564608
00564606
LF156 Large Signal Puls
Response, AV = +1
Inverter Settling Time
00564609
00564655
7
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LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical AC Performance Characteristics
LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical AC Performance Characteristics
Inverter Settling Time
(Continued)
Open Loop Frequency Response
00564656
00564657
Bode Plot
Bode Plot
00564658
00564659
Bode Plot
Common-Mode Rejection Ratio
00564660
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00564661
8
Power Supply Rejection Ratio
(Continued)
Power Supply Rejection Ratio
00564662
00564663
Undistorted Output Voltage Swing
Equivalent Input Noise Voltage
00564664
00564665
Equivalent Input Noise
Voltage (Expanded Scale)
00564666
9
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LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical AC Performance Characteristics
LF155/LF156/LF256/LF257/LF355/LF356/LF357
Detailed Schematic
00564613
*C = 3pF in LF357 series.
Connection Diagrams
(Top Views)
Dual-In-Line Package (M and N)
Metal Can Package (H)
00564614
Order Number LF155H, LF156H, LF256H, LF257H,
LF356BH, LF356H, or LF357H
See NS Package Number H08C
00564629
Order Number LF356M, LF356MX, LF355N, or LF356N
See NS Package Number M08A or N08E
*Available per JM38510/11401 or JM38510/11402
Application Hints
These are op amps with JFET input devices. These JFETs
have large reverse breakdown voltages from gate to source
and drain eliminating the need for clamps across the inputs.
Therefore large differential input voltages can easily be accommodated without a large increase in input current. The
maximum differential input voltage is independent of the
supply voltages. However, neither of the input voltages
should be allowed to exceed the negative supply as this will
cause large currents to flow which can result in a destroyed
unit.
Exceeding the negative common-mode limit on either input
will force the output to a high state, potentially causing a
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10
Typical Circuit Connections
(Continued)
reversal of phase to the output. Exceeding the negative
common-mode limit on both inputs will force the amplifier
output to a high state. In neither case does a latch occur
since raising the input back within the common-mode range
again puts the input stage and thus the amplifier in a normal
operating mode.
Exceeding the positive common-mode limit on a single input
will not change the phase of the output however, if both
inputs exceed the limit, the output of the amplifier will be
forced to a high state.
These amplifiers will operate with the common-mode input
voltage equal to the positive supply. In fact, the
common-mode voltage can exceed the positive supply by
approximately 100 mV independent of supply voltage and
over the full operating temperature range. The positive supply can therefore be used as a reference on an input as, for
example, in a supply current monitor and/or limiter.
Precautions should be taken to ensure that the power supply
for the integrated circuit never becomes reversed in polarity
or that the unit is not inadvertently installed backwards in a
socket as an unlimited current surge through the resulting
forward diode within the IC could cause fusing of the internal
conductors and result in a destroyed unit.
All of the bias currents in these amplifiers are set by FET
current sources. The drain currents for the amplifiers are
therefore essentially independent of supply voltage.
As with most amplifiers, care should be taken with lead
dress, component placement and supply decoupling in order
to ensure stability. For example, resistors from the output to
an input should be placed with the body close to the input to
minimize “pickup” and maximize the frequency of the feedback pole by minimizing the capacitance from the input to
ground.
A feedback pole is created when the feedback around any
amplifier is resistive. The parallel resistance and capacitance
from the input of the device (usually the inverting input) to AC
ground set the frequency of the pole. In many instances the
frequency of this pole is much greater than the expected 3dB
frequency of the closed loop gain and consequently there is
negligible effect on stability margin. However, if the feedback
pole is less than approximately six times the expected 3 dB
frequency a lead capacitor should be placed from the output
to the input of the op amp. The value of the added capacitor
should be such that the RC time constant of this capacitor
and the resistance it parallels is greater than or equal to the
original feedback pole time constant.
VOS Adjustment
00564667
•
•
•
VOS is adjusted with a 25k potentiometer
•
Typical overall drift: 5µV/˚C ± (0.5µV/˚C/mV of adj.)
The potentiometer wiper is connected to V+
For potentiometers with temperature coefficient of 100
ppm/˚C or less the additional drift with adjust is ≈ 0.5µV/
˚C/mV of adjustment
Driving Capacitive Loads
00564668
* LF155/6 R = 5k
LF357 R = 1.25k
Due to a unique output stage design, these amplifiers
have the ability to drive large capacitive loads and still
maintain stability. CL(MAX) . 0.01µF.
Overshoot ≤ 20%
Settling time (ts) . 5µs
LF357. A Large Power BW Amplifier
00564615
For distortion ≤ 1% and a 20 Vp-p VOUT swing, power bandwidth is:
500kHz.
11
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LF155/LF156/LF256/LF257/LF355/LF356/LF357
Application Hints
LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical Applications
Settling Time Test Circuit
00564616
•
•
•
•
Settling time is tested with the LF155/6 connected as unity gain inverter and LF357 connected for AV = −5
FET used to isolate the probe capacitance
Output = 10V step
AV = −5 for LF357
Large Signal Inverter Output, VOUT (from Settling Time Circuit)
LF355
LF357
00564619
00564617
LF356
00564618
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12
LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical Applications
(Continued)
Low Drift Adjustable Voltage Reference
00564620
•
•
•
•
•
∆ VOUT/∆T = ± 0.002%/˚C
All resistors and potentiometers should be wire-wound
P1: drift adjust
P2: VOUT adjust
Use LF155 for
j Low IB
j Low drift
j Low supply current
Fast Logarithmic Converter
00564621
•
•
•
•
•
Dynamic range: 100µA ≤ Ii ≤ 1mA (5 decades), |VO| = 1V/decade
Transient response: 3µs for ∆Ii = 1 decade
C1, C2, R2, R3: added dynamic compensation
VOS adjust the LF156 to minimize quiescent error
RT: Tel Labs type Q81 + 0.3%/˚C
13
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LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical Applications
(Continued)
Precision Current Monitor
00564631
•
•
•
VO = 5 R1/R2 (V/mA of IS)
R1, R2, R3: 0.1% resistors
Use LF155 for
j Common-mode range to supply range
j Low IB
j Low VOS
j Low Supply Current
8-Bit D/A Converter with Symmetrical Offset Binary Operation
00564632
•
•
R1, R2 should be matched within ± 0.05%
Full-scale response time: 3µs
EO
+9.920
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B1 B2 B3 B4 B5 B6 B7 B8
1
1
1
1
1
1
1
1
Comments
Positive Full-Scale
+0.040
1
0
0
0
0
0
0
0
(+) Zero-Scale
−0.040
0
1
1
1
1
1
1
1
(−) Zero-Scale
−9.920
0
0
0
0
0
0
0
0
Negative Full-Scale
14
LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical Applications
(Continued)
Wide BW Low Noise, Low Drift Amplifier
00564670
•
Parasitic input capacitance C1 . (3pF for LF155, LF156 and LF357 plus any additional layout capacitance) interacts with
feedback elements and creates undesirable high frequency pole. To compensate add C2 such that: R2 C2 . R1 C1.
Boosting the LF156 with a Current Amplifier
00564673
•
•
IOUT(MAX).150mA (will drive RL≥ 100Ω)
No additional phase shift added by the current amplifier
15
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LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical Applications
(Continued)
3 Decades VCO
00564624
R1, R4 matched. Linearity 0.1% over 2 decades.
Isolating Large Capacitive Loads
00564622
•
•
•
Overshoot 6%
ts 10µs
When driving large CL, the VOUT slew rate determined by CL and IOUT(MAX):
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16
LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical Applications
(Continued)
Low Drift Peak Detector
00564623
•
•
•
•
By adding D1 and Rf, VD1 =0 during hold mode. Leakage of D2 provided by feedback path through Rf.
Leakage of circuit is essentially Ib (LF155, LF156) plus capacitor leakage of Cp.
Diode D3 clamps VOUT (A1) to VIN−VD3 to improve speed and to limit reverse bias of D2.
Maximum input frequency should be << 1⁄2πRfCD2 where CD2 is the shunt capacitance of D2.
Non-Inverting Unity Gain Operation for LF157
00564675
Inverting Unity Gain for LF157
00564625
17
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LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical Applications
(Continued)
High Impedance, Low Drift Instrumentation Amplifier
00564626
•
•
System VOS adjusted via A2 VOS adjust
Trim R3 to boost up CMRR to 120 dB. Instrumentation amplifier resistor array recommended for best accuracy and lowest drift
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LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical Applications
(Continued)
Fast Sample and Hold
00564633
•
•
Both amplifiers (A1, A2) have feedback loops individually closed with stable responses (overshoot negligible)
•
•
•
LF156 develops full Sr output capability for VIN ≥ 1V
Acquisition time TA, estimated by:
Addition of SW2 improves accuracy by putting the voltage drop across SW1 inside the feedback loop
Overall accuracy of system determined by the accuracy of both amplifiers, A1 and A2
19
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LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical Applications
(Continued)
High Accuracy Sample and Hold
00564627
•
By closing the loop through A2, the VOUT accuracy will be determined uniquely by A1.
No VOS adjust required for A2.
•
TA can be estimated by same considerations as previously but, because of the added
propagation delay in the feedback loop (A2) the overshoot is not negligible.
•
•
•
Overall system slower than fast sample and hold
R1, CC: additional compensation
Use LF156 for
j Fast settling time
j Low VOS
High Q Band Pass Filter
00564628
•
•
•
By adding positive feedback (R2)
•
•
Clean layout recommended
Q increases to 40
fBP = 100 kHz
Response to a 1Vp-p tone burst: 300µs
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20
LF155/LF156/LF256/LF257/LF355/LF356/LF357
Typical Applications
(Continued)
High Q Notch Filter
00564634
•
2R1 = R = 10MΩ
2C = C1 = 300pF
•
•
•
Capacitors should be matched to obtain high Q
fNOTCH = 120 Hz, notch = −55 dB, Q > 100
Use LF155 for
j Low IB
j Low supply current
21
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LF155/LF156/LF256/LF257/LF355/LF356/LF357
Physical Dimensions
inches (millimeters) unless otherwise noted
Metal Can Package (H)
Order Number LF155H, LF156H, LF256H, LF257H, LF356BH, LF356H or LF357H
NS Package Number H08C
Small Outline Package (M)
Order Number LF356M or LF356MX
NS Package Number M08A
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22
inches (millimeters) unless otherwise noted (Continued)
Molded Dual-In-Line Package (N)
Order Number LF356N
NS Package Number N08E
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LF155/LF156/LF256/LF257/LF355/LF356/LF357 JFET Input Operational Amplifiers
Physical Dimensions
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