10

FN7312.5

January 25, 2006

Simplified Schematic

Description of Operation and Application

Information

Product Description

The EL5173 and EL5373 are wide bandwidth, low power

and single/differential ended to differential output amplifiers.

They have a fixed gain of 2. The EL5173 is a single channel

differential amplifier. The EL5373 is a triple channel

differential amplifier. The EL5173 and EL5373 have a –3dB

bandwidth of 450MHz while driving a 200

Ω differential load.

The EL5173 and EL5373 are available with a power down

feature to reduce the power while the amplifiers are

disabled.

Input, Output and Supply Voltage Range

The EL5173 and EL5373 have been designed to operate

with a single supply voltage of 5V to 10V or a split supplies

with its total voltage from 5V to 10V. The amplifiers have an

input common mode voltage range from -4.5V to 3.4V for

±5V supply. The differential mode input range (DMIR)

between the two inputs is from –2.3V to +2.3V. The input

voltage range at the REF pin is from –3.3V to 3.7V. If the

input common mode or differential mode signal is outside the

above-specified ranges, it will cause the output signal

distorted.

The output of the EL5173 and EL5373 can swing from –3.3V

to 3.6V at 200

Ω differential load at ±5V supply. As the load

resistance becomes lower, the output swing is reduced.

Differential and Common Mode Gain Settings

As shown at the simplified schematic, since the feedback

resistors RF and the gain resistor are integrated with 200

Ω

and 400

Ω, the EL5173 and EL5373 have a fixed gain of 2.

The common mode gain is always one.

Driving Capacitive Loads and Cables

The EL5173 and EL5373 can drive 16pF differential

capacitor in parallel with 200

Ω differential load with less than

3.5dB of peaking. If less peaking is desired in applications, a

small series resistor (usually between 5

Ω to 50Ω) can be

placed in series with each output to eliminate most peaking.

However, this will reduce the gain slightly.

When used as a cable driver, double termination is always

recommended for reflection-free performance. For those

applications, a back-termination series resistor at the

amplifier’s output will isolate the amplifier from the cable and

allow extensive capacitive drive. However, other applications

may have high capacitive loads without a back-termination

resistor. Again, a small series resistor at the output can help

to reduce peaking.

Disable/Power-Down

The EL5173 and EL5373 can be disabled and placed their

outputs in a high impedance state. The turn off time is about

1.2µs and the turn on time is about 100ns. When disabled,

power consumption. The amplifier’s power down can be

controlled by standard CMOS signal levels at the ENABLE

EN pin float or applying a signal that is less than 1.5V below

Output Drive Capability

The EL5173 and EL5373 have internal short circuit

protection. Its typical short circuit current is ±55mA. If the

output is shorted indefinitely, the power dissipation could

easily increase such that the part will be destroyed.

REF

OUT+

OUT-

FBN

FBP

IN-

IN+

200

Ω

200

Ω

400

Ω

EL5173, EL5373