EL2228

FN7008 Rev 2.00

Page 10 of 12

May 3, 2007

application does not come at the expense of stability. As

seen in the typical performance curves, the EL2228 in a gain

of only 1 exhibited 0.5dB of peaking with a 500

 load.

Output Drive Capability

The EL2228 is designed to drive a low impedance load. It

output drive capability makes the EL2228 an ideal choice for

RF, IF, and video applications. Furthermore, the EL2228 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 EL2228 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 Dissipation

With the wide power supply range and large output drive

capability of the EL2228, it is possible to exceed the 150°C

maximum junction temperatures under certain load and

power-supply conditions. It is therefore important to calculate

applications to determine if power supply voltages, load

conditions, or package type need to be modified for the

EL2228 to remain in the safe operating area. These

parameters are related as follows:

where:

where:

•

application

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. Pin 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.

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