EL2126CSZ datasheet(16/19 Pages) RENESAS

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EL2126

FN7046 Rev 4.00

Page 16 of 19

May 2, 2007

Output Drive Capability

The EL2126 is designed to drive low impedance load. It can

easily drive 6VP-P signal into a 100 load. This high output

drive capability makes the EL2126 an ideal choice for RF, IF,

and video applications. Furthermore, the EL2126 is

current-limited at the output, allowing it to withstand

momentary short to ground. However, the power dissipation

with output-shorted cannot exceed the power dissipation

capability of the package.

Driving Cables and Capacitive Loads

Although the EL2126 is designed to drive low impedance load,

capacitive loads will decreases the amplifier's phase margin.

As shown in the performance curves, capacitive load can result

in peaking, overshoot and possible oscillation. For optimum AC

performance, capacitive loads should be reduced as much as

possible or isolated with a series resistor between 5

 to 20.

When driving coaxial cables, double termination is always

recommended for reflection-free performance. When properly

terminated, the capacitance of the coaxial cable will not add to

the capacitive load seen by the amplifier.

Power Supply Bypassing And Printed Circuit Board

Layout

As with any high frequency devices, good printed circuit board

layout is essential for optimum performance. Ground plane

construction is highly recommended. Lead lengths should be

kept as short as possible. The power supply pins must be

closely bypassed to reduce the risk of oscillation. The

combination of a 4.7µF tantalum capacitor in parallel with

0.1µF ceramic capacitor has been proven to work well when

placed at each supply pin. For single supply operation, where

pin 4 (VS-) is connected to the ground plane, a single 4.7µF

tantalum capacitor in parallel with a 0.1µF ceramic capacitor

across pins 7 (VS+) and pin 4 (VS-) will suffice.

For good AC performance, parasitic capacitance should be

kept to a minimum. Ground plane construction again should be

used. Small chip resistors are recommended to minimize

series inductance. Use of sockets should be avoided since

they add parasitic inductance and capacitance which will result

in additional peaking and overshoot.

Supply Voltage Range and Single Supply Operation

The EL2126 has been designed to operate with supply voltage

range of ±2.5V to ±15V. With a single supply, the EL2126 will

operate from +5V to +30V. Pins 4 and 7 are the power supply

pins. The positive power supply is connected to pin 7. When

used in single supply mode, pin 4 is connected to ground.

When used in dual supply mode, the negative power supply is

connected to pin 4.

As the power supply voltage decreases from +30V to +5V, it

becomes necessary to pay special attention to the input

voltage range. The EL2126 has an input voltage range of 0.4V

from the negative supply to 1.2V from the positive supply. So,

for example, on a single +5V supply, the EL2126 has an input

voltage range which spans from 0.4V to 3.8V. The output range

of the EL2126 is also quite large, on a +5V supply, it swings

from 0.4V to 3.8V.

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