Application Hints

The LM2901EP is a high gain, wide bandwidth device which,

like most comparators, can easily oscillate if the output lead

is inadvertently allowed to capacitively couple to the inputs

via stray capacitance. This shows up only during the output

voltage transition intervals as the comparator changes

states. Power supply bypassing is not required to solve this

problem. Standard PC board layout is helpful as it reduces

stray input-output coupling. Reducing this input resistors to

Ω reduces the feedback signal levels and finally,

adding even a small amount (1 to 10 mV) of positive feed-

back (hysteresis) causes such a rapid transition that oscilla-

tions due to stray feedback are not possible. Simply socket-

ing the IC and attaching resistors to the pins will cause

input-output oscillations during the small transition intervals

unless hysteresis is used. If the input signal is a pulse

waveform, with relatively fast rise and fall times, hysteresis is

not required.

All pins of any unused comparators should be tied to the

negative supply.

The bias network of the LM2901EP series establishes a

drain current which is independent of the magnitude of the

power supply voltage over the range of from 2 V

V

It is usually unnecessary to use a bypass capacitor across

the power supply line.

The differential input voltage may be larger than V

damaging the device. Protection should be provided to pre-

vent the input voltages from going negative more than −0.3

V

in the applications section.

The output of the LM2901EP is the uncommitted collector of

a grounded-emitter NPN output transistor. Many collectors

can be tied together to provide an output OR’ing function. An

output pull-up resistor can be connected to any available

power supply voltage within the permitted supply voltage

range and there is no restriction on this voltage due to the

magnitude of the voltage which is applied to the V

of the LM2901EP package. The output can also be used as

a simple SPST switch to ground (when a pull-up resistor is

not used). The amount of current which the output device

can sink is limited by the drive available (which is indepen-

dent of V

β of this device. When the maximum

current limit is reached (approximately 16 mA), the output

transistor will come out of saturation and the output voltage

will rise very rapidly. The output saturation voltage is limited

by the approximately 60

Ω R

low offset voltage of the output transistor (1 mV) allows the

output to clamp essentially to ground level for small load

currents.

Basic Comparator

Driving CMOS

Driving TTL

20113903

20113904

20113905

AND Gate

20113908

OR Gate

20113909

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