10

Video Performance

For good video performance, an amplifier is required to

maintain the same output impedance and the same

frequency response as DC levels are changed at the output.

This is especially difficult when driving a standard video load

of 150

Ω, because of the change in output current with DC

level. Until the EL2480, good Differential Gain could only be

achieved by running high idle currents through the output

transistors (to reduce variations in output impedance). These

currents were typically comparable to the entire 3mA supply

current of EL2480 amplifier! Special circuitry has been

incorporated in the EL2480 to reduce the variation of output

impedance with current output. This results in dG and dP

specifications of 0.05% and 0.05° while driving 150

Ω at a

gain of +2.

Video performance has also been measured with a 500

Ω

load at a gain of +1. Under these conditions, the EL2480 has

dG and dP specifications of 0.01% and 0.01° respectively

while driving 500

Output Drive Capability

This amplifier of the EL2480 is capable of providing a

minimum of ±50mA. These output drive levels are

unprecedented in amplifiers running at these supply currents.

The ±50mA minimum output drive of the EL2480 amplifier

allows swings of ±2.5V into 50

Ω loads.

Driving Cables and Capacitive Loads

When used as a cable driver, double termination is always

recommended for reflection-free performance. For those

applications, the back-termination series resistor will decouple

the EL2480 from the cable and allow extensive capacitive

drive. However, other applications may have high capacitive

loads without a back-termination resistor. In these

applications, a small series resistor (usually between 5

Ω and

50

Ω) can be placed in series with the output to eliminate most

up for any gain loss which may be created by this additional

resistor at the output. In many cases it is also possible to

reduce the peaking.

Current Limiting

The EL2480 has no internal 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 destruction of the device.

Power Dissipation

With the high output drive capability of the EL2480, it is

possible to exceed the 150°C Absolute Maximum junction

temperature under certain very high load current conditions.

important to calculate the maximum junction temperature

voltages, load conditions, or package type need to be

modified for the EL2480 to remain in the safe operating area.

These parameters are calculated as follows:

where:

θ

n = Number of amplifiers in the package

the package

where:

T

JMAX

T

MAX

Θ

JA

nPD

MAX

×

×

()

+

=

PD

MAX

2

(

V

S

I

V

S

(

- V

V

OUTMAX

R

L

----------------------------

×

+

×

×

=

EL2480