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FN7046.4

May 2, 2007

Output Drive Capability

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

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

Ω to 20Ω. 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,

4.7µF tantalum capacitor in parallel with a 0.1µF ceramic

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.

EL2126