EL5191CSZ datasheet(16/20 Pages) INTERSIL

16 / 20 page

FN7180.3

May 16, 2007

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

EL5191 has an input range which extends to within 2V of

either supply. So, for example, on ±5V supplies, the EL5191

has an input range which spans ±3V. The output range of the

EL5191 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.

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.)

These currents were typically comparable to the entire 9mA

supply current of each EL5191 amplifier. Special circuitry

has been incorporated in the EL5191 to reduce the variation

of output impedance with current output. This results in dG

and dP specifications of 0.035% and 0.04°, while driving

150

Ω at a gain of 2.

Video performance has also been measured with a 500

load at a gain of +1. Under these conditions, the EL5191 has

dG and dP specifications of 0.02% and 0.02°, respectively.

Output Drive Capability

In spite of its low 9mA of supply current, the EL5191 is

capable of providing a minimum of ±95mA of output current.

With a minimum of ±95mA of output drive, the EL5191 is

capable of driving 50

Ω loads to both rails, making it an

excellent choice for driving isolation transformers in

telecommunications applications.

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 EL5191 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

Ω) 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 EL5191 has 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 EL5191, it is

possible to exceed the +125°C Absolute Maximum junction

temperature under certain very high load current conditions.

Generally speaking when RL falls below about 25Ω, it is

important to calculate the maximum junction temperature

(TJMAX) for the application to determine if power supply

voltages, load conditions, or package type need to be

modified for the EL5191 to remain in the safe operating area.

These parameters are calculated as follows:

where:

TMAX = Maximum ambient temperature

θJA = Thermal resistance of the package

n = Number of amplifiers in the package

PDMAX = Maximum power dissipation of each amplifier in

the package

PDMAX for each amplifier can be calculated as follows:

where:

VS = Supply voltage

ISMAX = Maximum supply current of 1A

VOUTMAX = Maximum output voltage (required)

RL = Load resistance

JMAX

MAX

nPD

MAX

()

MAX

(

SMAX )

(

- V

OUTMAX )

OUTMAX

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

EL5191, EL5191A

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