EL4441CS datasheet(11/16 Pages) ELANTEC

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EL4421C22C41C42C43C44C

Multiplexed-Input Video Amplifiers

Applications Information

Contd

The logic input(s) and ground pin are shifted

25V above system ground to correctly bias the

mux-amp Of course all the signal inputs and

output will have to be shifted 25V above system

ground to ensure proper signal path biasing

A final caution the ground pin is also connected

to the IC’s substrate and frequency compensation

components The ground pin must be returned to

system ground by a short wire or nearby bypass

capacitor In figure 2 the 22 K

X resistors also

serve to isolate the bypassed ground pin from the

5V supply noise

Signal Amplitudes

Signal input and output voltages must be be-

tween (V

)a25V and (Va)

25V to ensure

linearity Additionally the differential voltage on

any input stage must be limited to g6V to pre-

vent damage In unity-gain connections any in-

put could have g3V applied and the output

would be at g3V putting us at our 6V differen-

tial limit Higher-gain circuit applications divide

the output voltage and allow for larger outputs

For instance at a gain of a2 the maximum input

is again g3V and the output swing is g6V The

EL4443 or EL4444 can be wired for inverting

gain with even more amplitude possible

The output and positive inputs respond to over-

loading amplitudes correctly that is they simply

clamp and remain monotonic with increasing

input overdrive A condition exists however

where the

input of an active stage is overdriven

by large outputs This occurs mainly in unity-

gain connections and only happens for negative

inputs The overloaded input cannot control the

feedback loop correctly and the output can be-

come non-monotonic A typical scenario has the

circuit running on g5V supplies connected for

unity gain and the input is the maximum g3V

Negative input extremes can cause the output to

jump from

3V to around

23V This will nev-

er happen if the input is restricted to g25V

which is the guaranteed maximum input compli-

ance with g5V supplies and is not a problem

with greater supply voltages

Connecting the

feedback network with a divider will prevent the

overloaded output voltage from being large

enough to overload the

input and monotonic

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