5 - Offset Null 2
6 - Output
7 - V
CC
+
8 - N.C.
WIDE BANDWIDTH
SINGLE J-FET OPERATIONAL AMPLIFIERS
.
HIGH INPUT IMPEDANCE J-FET INPUT
STAGE
.
HIGH SPEED J-FET OP-AMPs : up to 20MHz,
50V/
s
.
OFFSET VOLTAGE ADJUSTMENT DOES NOT
DEGRADE DRIFT OR COMMON-MODE
REJECTION AS IN MOST OF MONOLITHIC
AMPLIFIERS
.
INTERNAL COMPENSATION AND LARGE
DIFFERENTIAL INPUT VOLTAGECAPABILITY
(UP TO V
CC
+
)
TYPICAL APPLICATIONS
.
PRECISION HIGH SPEED INTEGRATORS
.
FAST D/A AND CONVERTERS
.
HIGH IMPEDANCE BUFFERS
.
WIDEBAND, LOW NOISE, LOW DRIFT
AMPLIFIERS
.
LOGARITHIMIC AMPLIFIERS
.
PHOTOCELL AMPLIFIERS
.
SAMPLE AND HOLD CIRCUITS
N
DIP8
(Plastic Package)
1
2
3
4
8
6
5
7
1 - Offset Null 1
2 - Inverting input
3 - Non-inverting input
4 - V
CC
-
PIN CONNECTIONS (top view)
DESCRIPTION
These circuits are monolithic J-FET input operational
amplifiers incorporating well matched, high voltage
J-FET on the same chip with standard bipolar transis-
tors.
This amplifiers feature low input bias and offset cur-
rents, low input offset voltage and input offset voltage
drift,coupledwith offsetadjust which doesnot degrade
drift or common-mode rejection.
The devices are also designed for high slew rate, wide
bandwidth,extremelyfastsettlingtime, lowvoltageand
current noise and a low 1/f noise level.
LF155-LF255-LF355
LF156-LF256-LF356
LF157-LF257-LF357
July 1998
D
SO8
(Plastic Micropackage)
ORDER CODES
Part Number
Temperature
Range
Package
N
D
LF355, LF356, LF357
0
o
C, +70
o
C
LF255, LF256, LF257
40
o
C, +105
o
C
LF155, LF156, LF157
55
o
C, +125
o
C
Example : LF355N
1/14
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Value
Unit
V
CC
Supply Voltage
22
V
V
i
Input Voltage - (note 1)
20
V
V
id
Differential Input Voltage
40
V
P
tot
Power Dissipation
570
mW
Output Short-circuit Duration
Infinite
T
oper
Operating Free Air Temperature Range
LF155-LF156-LF157
LF255-LF256-LF257
LF355-LF356-LF357
-55 to +125
40 to +105
0 to 70
o
C
T
stg
Storage Temperature Range
65 to 150
o
C
SCHEMATIC DIAGRAM
V
i o
ADJUSTMENT
LF155 - LF156 - LF157
2/14
ELECTRICAL CHARACTERISTICS
LF155, LF156, LF157
-55
o
C
T
amb
+125
o
C
5V
V
CC
20V
LF255, LF256, LF257
-40
o
C
T
amb
+105
o
C
5V
V
CC
20V
(unless otherwise specified)
Symbol
Parameter
LF155 - LF156 - LF157
LF255 - LF256 - LF257
Unit
Min.
Typ.
Max.
V
io
Input Offset Voltage (R
S
= 50
)
T
amb
= 25
o
C
T
min.
T
amb
T
max.
LF155, LF156, LF157
LF255, LF256, LF257
3
5
7
6.2
mV
I
io
Input Offset Current - (note 3)
T
amb
= 25
o
C
T
min.
T
amb
T
max.
LF155, LF156, LF157
LF255, LF256, LF257
3
20
20
1
pA
nA
nA
I
ib
Input Bias Current - (note 3)
T
amb
= 25
o
C
T
min.
T
amb
T
max.
LF155, LF156, LF157
LF255, LF256, LF257
20
100
50
5
pA
nA
nA
A
vd
Large Signal Voltage Gain (R
L
= 2k
, V
O
=
10V, V
CC
=
15V)
T
amb
= 25
o
C
T
min.
T
amb
T
max.
50
25
200
V/mV
SVR
Supply Voltage Rejection Ratio - (note 4)
85
100
dB
I
CC
Supply Current (V
CC
=
15V, no load)
T
amb
= 25
o
C
LF155, LF255
LF156, LF256
LF157, LF257
2
5
5
4
7
7
mA
DV
io
Input Offset Voltage Drift (R
S
= 50
)
5
V/
o
C
DV
io
/V
io
Change in Average Temperature Coefficient with V
io
adjust
(R
S
= 50
) - (note 2)
0.5
V/
o
C
V
icm
Input Common Mode Voltage Range (V
CC
=
15V, T
amb
= 25
o
C)
11
+15.1
-12
V
CMR
Common Mode Rejection Ratio
85
100
dB
V
OPP
Output Voltage Swing (V
CC
=
15V)
R
L
= 10k
R
L
= 2k
12
10
13
12
V
GBP
Gain Bandwidth Product (V
CC
=
15V, T
amb
= 25
o
C)
LF155, LF255
LF156, LF256
LF157, LF257
2.5
5
20
MHz
SR
Slew Rate (V
CC
=
15V, T
amb
= 25
o
C)
A
V
= 1
LF155, LF255
LF156, LF256
A
V
= 5
LF157, LF257
7.5
30
5
12
50
V/
s
R
i
Input Resistance (T
amb
= 25
o
C)
10
12
C
i
Input Capacitance (V
CC
=
15V, T
amb
= 25
o
C)
3
pF
e
n
Equivalent Input Noise Voltage
(V
CC
=
15V, T
amb
= 25
o
C, R
S
= 100
)
f = 1000Hz
LF155, LF255
LF156, LF256
LF157, LF257
f = 100Hz
LF155, LF255
LF156, LF256
LF157, LF257
20
12
12
25
15
15
nV
Hz
i
n
Equivalent Input Noise Current
(V
CC
=
15V, T
amb
= 25
o
C, f = 100Hz or f = 1000Hz)
0.01
pA
Hz
t
s
Settling Time (V
CC
=
15V, T
amb
= 25
o
C) - (note 5)
LF155, LF255
LF156, LF256
LF157, LF257
4
1.5
1.5
s
LF155 - LF156 - LF157
3/14
Notes : 1. Unless otherwise specified the absolute maximum negative input voltage is equal to the negative power supply voltage.
2. The temperature coefficient of the adjusted input offset voltage changes only a small amount (0.5
V/
o
C typically) for each mV
of adjustment from its original unadjusted value. Common-mode rejection and open loop voltage gain are alsounaffected by
offset adjustment.
3. The input bias currents are junction leakage currents which approximately double for every 10
o
C increase in the junction
temperature T
amb
. Due to limited production test time, the input bias current measured is correlated to junction temperature.
In a normal operation the junction temperature rises above the ambient temperature as a result of internal power dissipation,
P
tot
-T
amb
=T
amb
+R
th(j-a)
xP
tot
where Rt
h(j-a)
is the thermal resistance from junction to ambient. Use of a heatsink is recommended
f input currents are to be kept to a minimum.
4. Supply voltage rejection is measured for both supply magnitudes increasing or decreasing simultaneously, in accordance with
common practise.
5. Settling time is defined here, for a unity gain inverter connection using 2k
resistors for the LF155, LF156 series. 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 LF157 series A
V
= -5, the feedback resistor from output to input is 2k
and the output step is 10V.
ELECTRICAL CHARACTERISTICS
LF355, LF356, LF357
0
o
C
T
amb
+70
o
C
V
CC
=
15V
, (unless otherwise specified)
Symbol
Parameter
LF355 - LF356 - LF357
Unit
Min.
Typ.
Max.
V
io
Input Offset Voltage (R
S
= 50
)
T
amb
= 25
o
C
T
min.
T
amb
T
max.
3
10
13
mV
I
io
Input Offset Current - (note 3)
T
amb
= 25
o
C
T
min.
T
amb
T
max.
3
50
2
pA
nA
I
ib
Input Bias Current - (note 3)
T
amb
= 25
o
C
T
min.
T
amb
T
max.
20
200
8
pA
nA
A
vd
Large Signal Voltage Gain (R
L
= 2k
, V
O
=
10V)
T
amb
= 25
o
C
T
min.
T
amb
T
max.
25
15
200
V/mV
SVR
Supply Voltage Rejection Ratio - (note 4)
80
100
dB
I
CC
Supply Current (no load)
T
amb
= 25
o
C
LF355
LF356, LF357
2
5
4
10
mA
DV
io
Input Offset Voltage Drift (R
S
= 50
) - (note 2)
5
V/
o
C
DV
io
/V
io
Change in Average Temperature Coefficient with V
io
adjust
(R
S
= 50
)
0.5
V/
o
C
per mV
V
icm
Input Common Mode Voltage Range (T
amb
= 25
o
C)
10
+15.1
-12
V
CMR
Common Mode Rejection Ratio
80
100
dB
V
OPP
Output Voltage Swing
R
L
= 10k
R
L
= 2k
12
10
13
12
V
GBP
Gain Bandwidth Product T
amb
= 25
o
C)
LF355
LF356
LF357
2.5
5
20
MHz
SR
Slew Rate (T
amb
= 25
o
C)
A
V
= 1
LF355
LF356
A
V
= 5
LF357
5
12
50
V/
s
R
i
Input Resistance (T
amb
= 25
o
C)
10
12
C
i
Input Capacitance (Tamb = 25
o
C)
3
pF
e
n
Equivalent Input Noise Voltage (T
amb
= 25
o
C, R
S
= 100
)
f = 1000Hz
LF355
LF356, LF357
f = 100Hz
LF355
LF356, LF357
20
12
25
15
nV
Hz
i
n
Equivalent Input Noise Current
(T
amb
= 25
o
C, f = 100Hz or f = 1000Hz)
0.01
pA
Hz
t
s
Settling Time (T
amb
= 25
o
C) - (note 5)
LF355
LF356, LF357
4
1.5
s
LF155 - LF156 - LF157
4/14
The LF155, LF156, LF157 series are op amps with J-
FETinput transistors. TheseJFETs havelarge reverse
breakdown voltagesfromgatetosource or drain elimi-
natingtheneed of clamps across the inputs.Therefore
large differential input voltages can easily be accom-
modatedwithoutalarge increaseof inputcurrents. The
maximum differential input voltage is independent of
the supply voltage. However, neitherof thenegativein-
put voltagesshouldbe allowed to exceedthe negative
supply as this will cause large currents to flow which
can result in a destroyed unit. Exceeding the negative
common-modelimit on either inputwill causeareversal
of thephasetotheoutputandforce the amplifier output
to the correspondinghigh or lowstate. Exceedingthe
negativecommon-mode limit on bothinputs will force
the amplifier outputto a highstate.In neithercasedoes
a latch occur since raising the input back within the
common-mode range again puts the input stage and
thustheamplifier in a normal operatingmode. Exceed-
ingthepositive common-modelimit on asingle input will
not changethephase of the output however, if bothin-
putsexceedthe limit, theoutput of theamplifier will be
forcedto ahighstate.Theseamplifiers will operatewith
the common-mode input voltage equal to the positive
supply. In fact, the common-modevoltagecanex-
ceedthepositivesupplyby approximately 100mV inde-
pendentof supply volt-age and over thefull operat-
ingtemperaturerange.The positive suplly can there-
forebe used as a referenceonaninput as, forexample,
in a supply current monitor and/or limiter. Precautions-
shouldbe taken to ensurethat thepowersupply for the
integrated circuit never becomes re-versed in polarity
or that the unit is not inadvertentlyin-stalledbackwards
in a socket as an unilimited current surge throughthe
resulting forward diode within the IC couldcausefusin-
goftheinternalconductorsandresultin a destroyedunit.
Because these amplifiers are JFET rather than MOS-
FET input op amps they do not require special han-
dling.
Allof thebiascurrentsintheseamplifiersareset by FET
current sources. The drain currents for the amplifiers
are therefore essentially independent of supply volt-
ages.
As with most amplifiers, care should betakenwith lead
dress, components 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 theinput to minimiz "pickup" and maximize the
frequency of the feedback pole by minimizing the ca-
pacitancefrom the input to ground.
A feedback pole is createdwhen the feedbackaround
any amplifier is resistive. The parallel resistance and
capacitancefromthe input of thedevice(usually the in-
vertinginput)toacgroundsetthefrequencyofthepole.In
many instances the frequency of this pole is much
greaterthanthe expected3 dBfrequencyof the closed
loopgain and consequentlythereisnegligible effect on
stability margin. However, if the feedback pole is less
than approximately six time the expected 3 dB fre-
quencyaleadcapacitor should be placed from the out-
put to the input of the op amp. The value of that 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 con-
stant.
APPLICATION HINTS
LF155 - LF156 - LF157
5/14
LF155 - LF156 - LF157
6/14
LF155 - LF156 - LF157
7/14
LF155 - LF156 - LF157
8/14
LF155 - LF156 - LF157
9/14
LF155 - LF156 - LF157
10/14
LF155 - LF156 - LF157
11/14
LF155 - LF156 - LF157
12/14
PM-DIP8.EPS
PACKAGE MECHANICAL DATA
8 PINS - PLASTIC DIP
Dimensions
Millimeters
Inches
Min.
Typ.
Max.
Min.
Typ.
Max.
A
3.32
0.131
a1
0.51
0.020
B
1.15
1.65
0.045
0.065
b
0.356
0.55
0.014
0.022
b1
0.204
0.304
0.008
0.012
D
10.92
0.430
E
7.95
9.75
0.313
0.384
e
2.54
0.100
e3
7.62
0.300
e4
7.62
0.300
F
6.6
0260
i
5.08
0.200
L
3.18
3.81
0.125
0.150
Z
1.52
0.060
DIP8.TBL
LF155 - LF156 - LF157
13/14
PM-SO8.EPS
PACKAGE MECHANICAL DATA
8 PINS - PLASTIC MICROPACKAGE (SO)
Dimensions
Millimeters
Inches
Min.
Typ.
Max.
Min.
Typ.
Max.
A
1.75
0.069
a1
0.1
0.25
0.004
0.010
a2
1.65
0.065
a3
0.65
0.85
0.026
0.033
b
0.35
0.48
0.014
0.019
b1
0.19
0.25
0.007
0.010
C
0.25
0.5
0.010
0.020
c1
45
o
(typ.)
D
4.8
5.0
0.189
0.197
E
5.8
6.2
0.228
0.244
e
1.27
0.050
e3
3.81
0.150
F
3.8
4.0
0.150
0.157
L
0.4
1.27
0.016
0.050
M
0.6
0.024
S
8
o
(max.)
SO8.TBL
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the
consequences of use of such information nor for any infringement of patents or other rights of third parties which may result
from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifi-
cations mentioned in this pub lication are subject to change without notice. This publication supersedes and replaces all infor-
mation previously supplied. STMicroelectronics products are not authorized for use as critical components in life support
devices or systems without express written approval of STMicroelectronics.
The ST log o is a trademark of STMicroelectronics
1998 STMicroelectronics Printed in Italy All Rights Reserved
STMicroelectronics GROUP OF COMPANIES
Australia - Brazil - Canada - China - France - Germany - Italy - Japan - Korea - Malaysia - Malta - Mexico - Morocco
The Netherlands - Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdo m - U.S.A.
ORDER
CODE
:
LF155 - LF156 - LF157
14/14
PDF 
ZIP