9

FN7103.9

September 14, 2010

EL8100, EL8101

some maximum value that should not be exceeded for

can help to reduce the ringing and peaking at the expense of

reducing the bandwidth.

As far as the output stage of the amplifier is concerned, the

combination gets smaller, the bandwidth falls off.

be exceeded for optimum performance. For gain of +1,

The EL8100, EL8101 have a gain bandwidth product of

100MHz. For gains

≥5, its bandwidth can be predicted by

Equation 1:

Video Performance

For good video performance, an amplifier is required to

maintain the same output impedance and the same

frequency response as DC levels are changed at the output.

This is especially difficult when driving a standard video load

of 150

Ω, because the change in output current with DC level.

Special circuitry has been incorporated in the

EL8100, EL8101 to reduce the variation of the output

impedance with the current output. This results in dG and dP

specifications of 0.03% and 0.05

°, while driving 150Ω at a

gain of 2. Driving high impedance loads would give a similar

or better dG and dP performance.

Driving Capacitive Loads and Cables

The EL8100, EL8101 can drive 15pF 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

which 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 EL8100 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 EL8100, EL8101 do not have internal short circuit

protection circuitry. They have a typical short circuit current

of 70mA sourcing and 140mA 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 EL8100, EL8101,

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 Equation 2:

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, Equation 3:

For sinking, Equation 4:

Where:

Gain BW

×

100MHz

=

(EQ. 1)

–

θ

JA

---------------------------------------------

=

(EQ. 2)

–

()

----------------

×

+

×

=

(EQ. 3)

–

() I

LOAD

×

+

×

=

(EQ. 4)