EL2170CS datasheet(12/16 Pages) ELANTEC

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EL2170CEL2270CEL2470C

70 MHz1 mA Current Mode Feedback Amplifiers

Applications Information

Contd

Video Performance has also been measured with

a 500

X load at a gain of a1 Under these condi-

tions the EL2170CEL2270CEL2470C have dG

and dP specifications of 001% and 002 respec-

tively while driving 500

X at AV ea1

Output Drive Capability

In spite of its low 1 mA of supply current the

EL2170C is capable of providing a minimum of

80 mA of output current Similarly each am-

plifier of the EL2270C and the EL2470C is capa-

ble of providing a minimum of g50 mA These

output drive levels are unprecedented in amplifi-

ers running at these supply currents With a min-

imum g80 mA of output drive the EL2170C is

capable of driving 50

X loads to g4V making it

an excellent choice for driving isolation trans-

formers

telecommunications

applications

Similarly the g50 mA minimum output drive of

each EL2270C and EL2470C amplifier allows

swings of g25V into 50

X loads

Driving Cables and Capacitive Loads

When used as a cable driver double termination

is always recommended for reflection-free per-

formance For those applications the back-termi-

nation series resistor will decouple the EL2170C

EL2270CEL2470C from the cable and allow ex-

tensive capacitive drive However other applica-

tions may have high capacitive loads without a

back-termination resistor In these applications a

small series resistor (usually between 5

X and

X) can be placed in series with the output to

eliminate most peaking The gain resistor (RG)

can then be chosen to make up for any gain loss

which may be created by this additional resistor

at the output In many cases it is also possible to

simply increase the value of the feedback resistor

(RF) to reduce the peaking

Current Limiting

The EL2170CEL2270CEL2470C have no inter-

nal current-limiting circuitry If any output is

shorted it is possible to exceed the Absolute

Maximum Ratings for output current or power

dissipation potentially resulting in the destruc-

tion of the device

Power Dissipation

With the high output drive capability of the

EL2170CEL2270CEL2470C

it is possible to

exceed the 150 C Absolute Maximum junction

temperature under certain very high load current

conditions Generally speaking when RL falls be-

low about 25

X it is important to calculate the

maximum junction temperature (TJMAX) for the

application to determine if power-supply volt-

ages load conditions or package type need to be

modified for the EL2170CEL2270CEL2470C to

remain in the safe operating area These parame-

ters are calculated as follows

TJMAX e TMAX a (iJA n PDMAX)

where

TMAX

Maximum Ambient Temperature

iJA

Thermal Resistance of the Package

Number of Amplifiers in the Pack-

age

PDMAX e Maximum Power Dissipation of

Each Amplifier in the Package

PDMAX for each amplifier can be calculated as

follows

PDMAX e (2 VS ISMAX) a

(VS b VOUTMAX) (VOUTMAX RL))

where

Supply Voltage

ISMAX

Maximum Supply Current of 1

Amplifier

VOUTMAX e Max Output Voltage of the Ap-

plication

Load Resistance

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