LF351N - National Semiconductor

TL/H/5648

LF351 Wide Bandwidth JFET Input Operational Amplifier

December 1995

LF351 Wide Bandwidth JFET Input Operational Amplifier

General Description

The LF351 is a low cost high speed JFET input operational

amplifier with an internally trimmed input offset voltage

(BI-FET IITM technology). The device requires a low supply

current and yet maintains a large gain bandwidth product

and a fast slew rate. In addition, well matched high voltage

JFET input devices provide very low input bias and offset

currents. The LF351 is pin compatible with the standard

LM741 and uses the same offset voltage adjustment circuit-

ry. This feature allows designers to immediately upgrade the

overall performance of existing LM741 designs.

The LF351 may be used in applications such as high speed

integrators, fast D/A converters, sample-and-hold circuits

and many other circuits requiring low input offset voltage,

low input bias current, high input impedance, high slew rate

and wide bandwidth. The device has low noise and offset

voltage drift, but for applications where these requirements

are critical, the LF356 is recommended. If maximum supply

current is important, however, the LF351 is the better

choice.

Features

YInternally trimmed offset voltage 10 mV

YLow input bias current 50 pA

YLow input noise voltage 25 nV/0Hz

YLow input noise current 0.01 pA/0Hz

YWide gain bandwidth 4 MHz

YHigh slew rate 13 V/ms

YLow supply current 1.8 mA

YHigh input impedance 1012X

YLow total harmonic distortion AVe10, k0.02%

RLe10k, VOe20 Vp-p, BWe20 Hz–20 kHz

YLow 1/f noise corner 50 Hz

YFast settling time to 0.01% 2 ms

Typical Connection

TL/H/5648–11

Simplified Schematic

TL/H/5648–12

Connection Diagrams

Dual-In-Line Package

TL/H/5648–13

Order Number LF351M or LF351N

See NS Package Number M08A or N08E

C1995 National Semiconductor Corporation RRD-B30M125/Printed in U. S. A.

Absolute Maximum Ratings

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales

Office/Distributors for availability and specifications.

Supply Voltage g18V

Power Dissipation (Notes 1 and 6) 670 mW

Operating Temperature Range 0§Ctoa

70§C

Tj(MAX) 115§C

Differential Input Voltage g30V

Input Voltage Range (Note 2) g15V

Output Short Circuit Duration Continuous

Storage Temperature Range b65§Ctoa

150§C

Lead Temp. (Soldering, 10 sec.)

Metal Can 300§C

DIP 260§C

ijA

N Package 120§C/W

M Package TBD

Soldering Information

Dual-In-Line Package

Soldering (10 sec.) 260§C

Small Outline Package

Vapor Phase (60 sec.) 215§C

Infrared (15 sec.) 220§C

See AN-450 ‘‘Surface Mounting Methods and Their Effect

on Product Reliability’’ for other methods of soldering sur-

face mount devices.

ESD rating to be determined.

DC Electrical Characteristics (Note 3)

Symbol Parameter Conditions LF351 Units

Min Typ Max

VOS Input Offset Voltage RSe10 kX,T

Ae25§C 5 10 mV

Over Temperature 13 mV

DVOS/DT Average TC of Input Offset RSe10 kX10 mV/§C

Voltage

IOS Input Offset Current Tje25§C, (Notes 3, 4) 25 100 pA

Tjs70§C4nA

Input Bias Current Tje25§C, (Notes 3, 4) 50 200 pA

Tjsg70§C8nA

IN Input Resistance Tje25§C10

12 X

AVOL Large Signal Voltage Gain VSeg15V, TAe25§C 25 100 V/mV

VOeg10V, RLe2kX

Over Temperature 15 V/mV

VOOutput Voltage Swing VSeg15V, RLe10 kXg12 g13.5 V

VCM Input Common-Mode Voltage a15 V

Range VSeg15V g11

b12 V

CMRR Common-Mode Rejection Ratio RSs10 kX70 100 dB

PSRR Supply Voltage Rejection Ratio (Note 5) 70 100 dB

ISSupply Current 1.8 3.4 mA

AC Electrical Characteristics (Note 3)

Symbol Parameter Conditions LF351 Units

Min Typ Max

SR Slew Rate VSeg15V, TAe25§C13 V/ms

GBW Gain Bandwidth Product VSeg15V, TAe25§C 4 MHz

enEquivalent Input Noise Voltage TAe25§C, RSe100X,25 nV/0Hz

fe1000 Hz

inEquivalent Input Noise Current Tje25§C, fe1000 Hz 0.01 pA/0Hz

Note 1: For operating at elevated temperature, the device must be derated based on the thermal resistance, iJA.

Note 2: Unless otherwise specified the absolute maximum negative input voltage is equal to the negative power supply voltage.

Note 3: These specifications apply for VSeg15V and 0§CsTAsa70§C. VOS,I

Band IOS are measured at VCMe0.

Note 4: The input bias currents are junction leakage currents which approximately double for every 10§C increase in the junction temperature, Tj. Due to the 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

jA PDwhere ijA 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 5: Supply voltage rejection ratio is measured for both supply magnitudes increasing or decreasing simultaneously in accordance with common practice. From

g15V to g5V.

Note 6: 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 Performance Characteristics

Input Bias Current Input Bias Current Supply Current

Positive Common-Mode

Input Voltage Limit

Negative Common-Mode

Input Voltage Limit Positive Current Limit

Negative Current Limit Voltage Swing Output Voltage Swing

Gain Bandwidth Bode Plot Slew Rate

TL/H/5648–2

Typical Performance Characteristics (Continued)

Distortion vs Frequency

Undistorted Output

Voltage Swing

Open Loop Frequency

Response

Common-Mode

Rejection Ratio

Power Supply

Rejection Ratio

Equivalent Input

Noise Voltage

Open Loop Voltage

Gain (V/V) Output Impedance Inverter Settling Time

TL/H/5648–3

Pulse Response

Small Signal Inverting

TL/H/5648–4

Small Signal Non-Inverting

TL/H/5648–5

Large Signal Inverting

TL/H/5648–6

Large Signal Non-Inverting

TL/H/5648–7

Current Limit (RLe100X)

TL/H/5648–8

Application Hints

The LF351 is an op amp with an internally trimmed input

offset voltage and JFET input devices (BI-FET IITM ). 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

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

Application Hints (Continued)

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.

The amplifier will operate with a common-mode input volt-

age equal to the positive supply; however, the gain band-

width and slew rate may be decreased in this condition.

When the negative common-mode voltage swings to within

3V of the negative supply, an increase in input offset voltage

may occur.

The LF351 is biased by a zener reference which allows nor-

mal circuit operation on g4V power supplies. Supply volt-

ages less than these may result in lower gain bandwidth and

slew rate.

The LF351 will drivea2kXload resistance to g10V over

the full temperature range of 0§Ctoa

70§C. If the amplifier

is forced to drive heavier load currents, however, an in-

crease in input offset voltage may occur on the negative

voltage swing and finally reach an active current limit on

both positive and negative swings.

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 back-

wards 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.

As with most amplifiers, care should be taken with lead

dress, component placement and supply decoupling in or-

der to ensure stability. For example, resistors from the out-

put to an input should be placed with the body close to the

input to minimize ‘‘pick-up’’ 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 capaci-

tance from the input of the device (usually the inverting in-

put) to AC ground set the frequency of the pole. In many

instances the frequency of this pole is much greater than

the expected 3 dB frequency of the closed loop gain and

consequently there is negligible effect on stability margin.

However, if the feedback pole is less than approximately 6

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.

Detailed Schematic

TL/H/5648–9

Typical Applications

Supply Current Indicator/Limiter

#VOUT switches high when RSISlVD

Hi-ZIN Inverting Amplifier

Parasitic input capacitance C1 j(3 pF for LF351

plus any additional layout capacitance) interacts

with feedback elements and creates undesirable

high frequency pole. To compensate, add C2 such

that: R2C2 jR1C1.

Ultra-Low (or High) Duty Cycle

Pulse Generator

#tOUTPUT HIGH &R1C ﬁn4.8 b2VS

4.8 bVS

#tOUTPUT LOW &R2C ﬁn2VSb7.8

VSb7.8

where VSeVaa

*low leakage capacitor

Long Time Integrator

*Low leakage capacitor

#50k pot used for less sensitive VOS adjust

TL/H/5648–10

Physical Dimensions inches (millimeters)

SO Package (M)

Order Number LF351M

NS Package Number M08A

LF351 Wide Bandwidth JFET Input Operational Amplifier

Physical Dimensions inches (millimeters) (Continued)

Molded Dual-In-Line Package (N)

Order Number LF351N

NS Package Number N08E

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