9

therefore capable of swinging from -4V to +4V. Single-supply

output range is even larger because of the increased

negative swing due to the external pull-down resistor to

ground. On a single +5V supply, output voltage range is

about 0.3V to 4V.

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 EL2270, 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 more than the entire 1mA supply

current of each EL2270 amplifier! Special circuitry has been

incorporated in the EL2270 to reduce the variation of output

impedance with current output. This results in dG and dP

specifications of 0.15% and 0.15° 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 EL2270 has

dG and dP specifications of 0.01% and 0.02° respectively

while driving 500

Output Drive Capability

In spite of its low 1mA of supply current, each amplifier of the

EL2270 is capable of providing a minimum of ±50mA. These

output drive levels are unprecedented in amplifiers running

at these supply currents. With a minimum ±80mA of output

drive, the ±50mA minimum output drive of each EL2270

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 EL2270 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

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

Current Limiting

The EL2270 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 EL2270, 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 EL2270 to remain in the safe operating area.

These parameters are calculated as follows [1]:

where:

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

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

×

+

×

×

=

EL2270