EL4451CS datasheet(8/12 Pages) ELANTEC

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EL4451C

Wideband Variable-Gain Amplifier Gain of 2

Applications Information

Contd

Signal Amplitudes

Signal input common-mode voltage must be be-

tween (Vb)a3V and (Va)b3V to ensure linear-

ity Additionally the differential voltage on any

input stage must be limited to g6V to prevent

damage The differential signal range is g2V in

the EL4451 The input range is substantially con-

stant with temperature

The Ground Pin

The ground pin draws only 6

mA maximum DC

current and may be biased anywhere between

(Vb)a25V and (Va)b35V The ground pin is

connected to the IC’s substrate and frequency

compensation components It serves as a shield

within the IC and enhances input stage CMRR

and feedthrough over frequency and if connected

to a potential other than ground it must be by-

passed

Power Supplies

The EL4451 works with any supplies from g3V

to g15V The supplies may be of different volt-

ages as long as the requirements of the ground

pin are observed (see the Ground Pin section)

The supplies should be bypassed close to the de-

vice with short leads 47

mF tantalum capacitors

are very good and no smaller bypasses need be

placed in parallel Capacitors as small as 001

can be used if small load currents flow

Single-polarity supplies

such as a12V with

5V can be used where the ground pin is con-

nected to a5V and Vb to ground The inputs

and outputs will have to have their levels shifted

above ground to accommodate the lack of nega-

tive supply

The power dissipation of the EL4451 increases

with power supply voltage and this must be

compatible with the package chosen This is a

close estimate for the dissipation of a circuit

PD e 2 c VS c IS max a (VS b VO) c VO RPAR

where IS max is the maximum supply current

VS is the g supply voltage (assumed

equal)

VO is the output voltage

RPAR is the parallel of all resistors loading

the output

For instance the EL4451 draws a maximum of

18mA With light loading RPAR

x% and the

dissipation with g5V supplies is 180 mW The

maximum supply voltage that the device can run

on for a given PD and other parameters is

VS max e (PD a VO2 RPAR) (2IS a VO RPAR)

The maximum dissipation a package can offer is

PD max e (TJ maxbTA max) iJA

Where

TJ max is the maximum die tempera-

ture 150 C for reliability less to re-

tain optimum electrical performance

TA max is the ambient temperature

70 C for commercial and 85 C for in-

dustrial range

iJA is the thermal resistance of the

mounted

package

obtained

from

data sheet dissipation curves

The more difficult case is the SO-14 package

With a maximum die temperature of 150 C and a

maximum ambient temperature of 85 C the 65 C

temperature rise and package thermal resistance

of 120 CW gives a dissipation of 542 mW at

85 C This allows the full maximum operating

supply voltage unloaded but reduced if loaded

Output Loading

The output stage of the EL4451 is very powerful

It typically can source 80mA and sink 120mA Of

course this is too much current to sustain and

the part will eventually be destroyed by excessive

dissipation or by metal traces on the die opening

The metal traces are completely reliable while de-

livering the 30mA continuous output given in the

Absolute Maximum Ratings table in this data

sheet or higher purely transient currents

Gain changes only 02% from no load to 100

load Heavy resistive loading will degrade fre-

quency response and video distortion for loads

100

Capacitive loads will cause peaking in the fre-

quency response If capacitive loads must be driv-

en a small-valued series resistor can be used to

isolate it 12

X to 51X should suffice A 22X series

resistor will limit peaking to 25 dB with even a

220pF load

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