10

Driving Capacitive Loads and Cables

The EL8302 can drive 5pF loads in parallel with 1k

Ω with

less than 5dB of peaking at gain of +1. If less peaking is

desired in applications, a small series resistor (usually

between 5

Ω to 50Ω) can be placed in series with the output

to eliminate most peaking. However, this will reduce the gain

slightly. If the gain setting is greater than 1, the gain resistor

may be created by the additional series resistor at the

output.

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 EL8302 can be disabled and placed its output in a high

impedance state. The turn off time is about 25ns and the turn

on time is about 200ns. When disabled, the amplifier’s

supply current is reduced to 30µA typically, thereby

effectively eliminating the power consumption. The

amplifier’s power down can be controlled by standard TTL or

CMOS signal levels at the ENABLE pin. The applied logic

the amplifier. The amplifier will be disabled when the signal

Output Drive Capability

The EL8302 does not have internal short circuit protection

circuitry. They have a typical short circuit current of 80mA

sourcing and 150mA sinking for the output is connected to

half way between the rails with a 10

Ω resistor. If the output is

shorted indefinitely, the power dissipation could easily

increase such that the part will be destroyed. Maximum

reliability is maintained if the output current never exceeds

±40mA. This limit is set by the design of the internal metal

interconnections.

Power Dissipation

With the high output drive capability of the EL8302, It is

possible to exceed the 125

°C absolute maximum junction

temperature under certain load current conditions.

Therefore, it is important to calculate the maximum junction

temperature for the application to determine if the load

conditions or package types need to be modified for the

amplifier to remain in the safe operating area.

The maximum power dissipation allowed in a package is

determined according to:

Where:

The maximum power dissipation actually produced by an IC

is the total quiescent supply current times the total power

supply voltage, plus the power in the IC due to the load, or:

For sourcing:

For sinking:

Where:

each channel

channel

overheat.

Power Supply Bypassing and Printed Circuit

Board Layout

As with any high frequency device, a good printed circuit

board layout is necessary for optimum performance. Lead

lengths should be as short as possible. The power supply

pin must be well bypassed to reduce the risk of oscillation.

connected to the ground plane, a single 4.7µF tantalum

to GND will suffice. This same capacitor combination should

be placed at each supply pin to ground if split supplies are to

supply rail.

For good AC performance, parasitic capacitance should be

kept to a minimum. Use of wire wound resistors should be

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EL8302