EL2252C 데이터 시트보기 (PDF) - Elantec -> Intersil

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EL2252C

Dual 50 MHz Comparator/Pin Receiver

Elantec -> Intersil 

EL2252C

Dual 50 MHz Comparator Pin Receiver

Applications Information Contd

One of the few ways in which oscillations can be

induced is by connecting a high-Q reactive source

impedance to the EL2252 inputs Such sources

are long wires and unterminated coaxial lines

The source impedance should be de-Q’ed One

method is to connect a series resistor to the

EL2252 input of around 100X value More resist-

ance will calm the system more effectively but at

the expense of comparator response time Anoth-

er method is to install a ‘‘snubber’’ network from

comparator input to ground A snubber is a resis-

tor in series with a small capacitor around 100X

and 33 pF Each physical and electrical environ-

ment will require different treatments although

many need none

The major use of the HYS pin is to suppress

noise superimposed on the input signal By

shorting the HYS pin to Vb a g30 mV hystere-

sis is placed around the VOS of the comparator

input Leaving the pin open or more appropri-

ately grounding the HYS pin removes all hyster-

esis Connecting a resistor between HYS and

Vb allows an adjustment of the peak-to-peak

hysteresis level Unfortunately an external resis-

tor cannot track the internal devices properly so

temperature and unit-to-unit variations of hys-

teresis are increased The relationship between

the resistor and resulting hysteresis level is not

linear but a 1 5k resistor will approximately

halve the nominal value

The time delay of the EL2252 will increase by

about 0 7 ns when using full hysteresis

The EL2252 is specifically designed to be tolerent

of large inputs It will exhibit very much in-

creased delay times for input overdrives below

100 mV If very small overdrives must be sensed

the EL2018 or EL2019 comparators would be

good choices although they lose accuracies with

signal input Slew Rates above 400 V ms The

EL2252 keeps its timing accuracy with input

Slew Rates between 100 V ms and 4000 V ms of

input Slew Rate

The output stage drives tens of pF load capaci-

tances without increased overshoot but propaga-

tion delay increases about 1 ns per 10 pF The

output circuit is not a traditional TTL stage and

using an external pullup resistor will not change

the VOH In general setting the output swing to

TTL (by grounding the TTL pin) will optimize

overall propagation delay and gswing symme-

try

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