LF155/LF156/LF256/LF257/LF355/LF356/LF357
JFET Input Operational Amplifiers
General Description
These are the first monolithic JFET input operational ampli-
fiers to incorporate well matched, high voltage JFETs on the
same chip with standard bipolar transistors (BI-FET
TM
Tech-
nology). 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
Applications
n
Precision high speed integrators
n
Fast D/A and A/D converters
n
High impedance buffers
n
Wideband, low noise, low drift amplifiers
n
Logarithmic amplifiers
n
Photocell amplifiers
n
Sample and Hold circuits
Common Features
n
Low input bias current:
30pA
n
Low Input Offset Current:
3pA
n
High input impedance:
10
12
n
Low input noise current:
n
High common-mode rejection ratio:
100 dB
n
Large dc voltage gain:
106 dB
Uncommon Features
LF155/
LF355
LF156/
LF256/
LF356
LF257/
LF357
(A
V
=5)
Units
j
Extremely
fast settling
time to
0.01%
4
1.5
1.5
s
j
Fast slew
rate
5
12
50
V/s
j
Wide gain
bandwidth
2.5
5
20
MHz
j
Low input
noise
voltage
20
12
12
Simplified Schematic
00564601
*
3pF in LF357 series.
BI-FET
TM
, BI-FET II
TM
are trademarks of National Semiconductor Corporation.
December 2001
LF155/LF156/LF256/LF257/LF355/LF356/LF357
JFET
Input
Operational
Amplifiers
2001 National Semiconductor Corporation
DS005646
www.national.com
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
Supply Voltage
22V
22V
18V
Differential Input Voltage
40V
40V
30V
Input Voltage Range (Note 2)
20V
20V
16V
Output Short Circuit Duration
Continuous
Continuous
Continuous
T
JMAX
H-Package
150C
115C
115C
N-Package
100C
100C
M-Package
100C
100C
Power Dissipation at T
A
= 25C (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
Thermal Resistance (Typical)
JA
H-Package (Still Air)
160C/W
160C/W
160C/W
H-Package (400 LF/Min Air Flow)
65C/W
65C/W
65C/W
N-Package
130C/W
130C/W
M-Package
195C/W
195C/W
(Typical)
JC
H-Package
23C/W
23C/W
23C/W
Storage Temperature Range
-65C to +150C
-65C to +150C
-65C to +150C
Soldering Information (Lead Temp.)
Metal Can Package
Soldering (10 sec.)
300C
300C
300C
Dual-In-Line Package
Soldering (10 sec.)
260C
260C
260C
Small Outline Package
Vapor Phase (60 sec.)
215C
215C
Infrared (15 sec.)
220C
220C
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 1.5k
)
1000V
1000V
1000V
DC Electrical Characteristics
(Note 3)
Symbol
Parameter
Conditions
LF155/6
LF256/7
LF356B
LF355/6/7
Units
Min
Typ
Max Min
Typ
Max Min
Typ
Max
V
OS
Input Offset Voltage
R
S
=50
, T
A
=25C
3
5
3
5
3
10
mV
Over Temperature
7
6.5
13
mV
V
OS
/
T
Average TC of Input
Offset Voltage
R
S
=50
5
5
5
V/C
TC/
V
OS
Change in Average TC
with V
OS
Adjust
R
S
=50
, (Note 4)
0.5
0.5
0.5
V/C
per mV
I
OS
Input Offset Current
T
J
=25C, (Notes 3, 5)
3
20
3
20
3
50
pA
T
J
T
HIGH
20
1
2
nA
LF155/LF156/LF256/LF257/LF355/LF356/LF357
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2
DC Electrical Characteristics
(Continued)
(Note 3)
Symbol
Parameter
Conditions
LF155/6
LF256/7
LF356B
LF355/6/7
Units
Min
Typ
Max Min
Typ
Max Min
Typ
Max
I
B
Input Bias Current
T
J
=25C, (Notes 3, 5)
30
100
30
100
30
200
pA
T
J
T
HIGH
50
5
8
nA
R
IN
Input Resistance
T
J
=25C
10
12
10
12
10
12
A
VOL
Large Signal Voltage
Gain
V
S
=
15V, T
A
=25C
50
200
50
200
25
200
V/mV
V
O
=
10V, R
L
=2k
Over Temperature
25
25
15
V/mV
V
O
Output Voltage Swing
V
S
=
15V, R
L
=10k
12
13
12
13
12
13
V
V
S
=
15V, R
L
=2k
10
12
10
12
10
12
V
V
CM
Input Common-Mode
Voltage Range
V
S
=
15V
11
+15.1
11
15.1
+10
+15.1
V
-12
-12
-12
V
CMRR
Common-Mode
Rejection Ratio
85
100
85
100
80
100
dB
PSRR
Supply Voltage
Rejection Ratio
(Note 6)
85
100
85
100
80
100
dB
DC Electrical Characteristics
T
A
= T
J
= 25C, V
S
=
15V
Parameter
LF155
LF355
LF156/256/257/356B
LF356
LF357
Units
Typ
Max
Typ
Max
Typ
Max
Typ
Max
Typ
Max
Supply
Current
2
4
2
4
5
7
5
10
5
10
mA
AC Electrical Characteristics
T
A
= T
J
= 25C, V
S
=
15V
Symbol
Parameter
Conditions
LF155/355
LF156/256/
356B
LF156/256/356/
LF356B
LF257/357
Units
Typ
Min
Typ
Typ
SR
Slew Rate
LF155/6:
A
V
=1,
5
7.5
12
V/s
LF357: A
V
=5
50
V/s
GBW
Gain Bandwidth Product
2.5
5
20
MHz
t
s
Settling Time to 0.01%
(Note 7)
4
1.5
1.5
s
e
n
Equivalent Input Noise
Voltage
R
S
=100
f=100 Hz
25
15
15
f=1000 Hz
20
12
12
i
n
Equivalent Input Current
Noise
f=100 Hz
0.01
0.01
0.01
f=1000 Hz
0.01
0.01
0.01
C
IN
Input Capacitance
3
3
3
pF
Notes for Electrical Characteristics
Note 1: The maximum power dissipation for these devices must be derated at elevated temperatures and is dictated by T
JMAX
,
JA
, and the ambient temperature,
T
A
. The maximum available power dissipation at any temperature is P
D
=(T
JMAX
-T
A
)/
JA
or the 25C P
dMAX
, 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:
LF155/LF156/LF256/LF257/LF355/LF356/LF357
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3
Notes for Electrical Characteristics
(Continued)
LF155/156
LF256/257
LF356B
LF355/6/7
Supply Voltage, V
S
15V
V
S
20V
15V
V
S
20V
15V
V
S
20V
V
S
=
15V
T
A
-55C
T
A
+125C
-25C
T
A
+85C
0C
T
A
+70C
0C
T
A
+70C
T
HIGH
+125C
+85C
+70C
+70C
and V
OS
, I
B
and I
OS
are measured at V
CM
= 0.
Note 4: The Temperature Coefficient of the adjusted input offset voltage changes only a small amount (0.5V/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 10C increase in the junction temperature, T
J
. 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. T
J
= T
A
+
JA
Pd where
JA
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 k
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, A
V
= -5,
the feedback resistor from output to input is 2k
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
00564637
00564638
Input Bias Current
Voltage Swing
00564639
00564640
LF155/LF156/LF256/LF257/LF355/LF356/LF357
www.national.com
4
Typical DC Performance Characteristics
Curves are for LF155 and LF156 unless otherwise
specified. (Continued)
Supply Current
Supply Current
00564641
00564642
Negative Current Limit
Positive Current Limit
00564643
00564644
Positive Common-Mode
Input Voltage Limit
Negative Common-Mode
Input Voltage Limit
00564645
00564646
LF155/LF156/LF256/LF257/LF355/LF356/LF357
www.national.com
5
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