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 LF451 is biased by a zener reference which allows nor-

ages less than these may result in lower gain bandwidth and

slew rate

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 sup-

ply for the integrated circuit never becomes reversed in po-

larity or that the unit is not inadvertently installed backwards

in a socket as an unlimited current surge through the result-

ing 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

The benefit of the SO package results from its very small

size It follows however that the die inside the SO pack-

age is less protected from external physical forces than a

die in a standard DIP would be because there is so much

less plastic in the SO Therefore not following certain pre-

cautions when board mounting the LF451CM can put me-

chanical stress on the die lead frame andor bond wires

This can cause shifts in the LF451CM’s parameters even

causing them to exceed limits specified in the Electrical

Characteristics For recommended practices in LF451CM

surface mounting refer to Application Note AN-450 ‘‘Sur-

face Mounting Methods and Their Effect on Product Reli-

ability’’ and to Section 6 ‘‘Surface Mount’’ found in any

Rev 1 Linear Databook volume

Detailed Schematic

TLH9660 – 11

6