9

Supply Voltage Range and Single-Supply

Operation

The EL5108 and EL5308 have been designed to operate

with supply voltages having a span of greater than or equal

to 5V and less than 12V. In practical terms, this means that

they will operate on dual supplies ranging from ±2.5V to ±5V.

With single-supply, they will operate from 5V to 10V.

As supply voltages continue to decrease, it becomes

necessary to provide input and output voltage ranges that

can get as close as possible to the supply voltages. The

EL5108 and EL5308 have an input range which extends to

within 2V of either supply. So, for example, on ±5V supplies,

the input range is about ±3V. The output range is also quite

large, extending to within 1V of the supply rail. On a ±5V

supply, the output is therefore capable of swinging from -4V

to +4V. Single-supply output range is larger because of the

increased negative swing due to the external pull-down

resistor to ground. Figure 24 shows an AC-coupled, gain of

+2, +5V single supply circuit configuration.

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. Previously, good differential gain could only be

achieved by running high idle currents through the output

transistors (to reduce variations in output impedance).

Special circuitry has been incorporated in the EL5108 and

EL5308 to reduce the variation of output impedance with

current output. This results in dG and dP specifications of

0.01% and 0.01°, while driving 150

Ω at a gain of 2.

Output Drive Capability

In spite of its low 3.5mA of supply current per amplifier, the

EL5108 and EL5308 are capable of providing a maximum of

±130mA of output current.

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 EL5108 and EL5308 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 50Ω) can be placed in series with the

output to eliminate most peaking.

Current Limiting

The EL5108 and EL5308 have no internal current-limiting

circuitry. If the output is shorted, it is possible to exceed the

Absolute Maximum Rating for output current or power

dissipation, potentially resulting in the destruction of the

device.

Power Dissipation

With the high output drive capability of the EL5108 and

EL5308, it is possible to exceed the 125°C Absolute

Maximum junction temperature under certain very high load

about 25

Ω, it is important to calculate the maximum junction

power supply voltages, load conditions, or package type

need to be modified for the EL5108 and EL5308 to remain in

the safe operating area. These parameters are calculated as

follows:

-

+

325

Ω

325

Ω

IN-

GND

-

+

325

Ω

325

Ω

IN-

IN+

FIGURE 24.

-

+

325

Ω

325

Ω

+5

0.1µF

1K

1K

0.1µF

+5

4.7µF

T

JMAX

T

MAX

θ

JA

nPD

MAX

×

×

()

+

=

EL5108, EL5308