11

FN7105.3

March 9, 2006

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 EL8200, EL8201

and EL8401, 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

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 sort as possible. The power supply pin

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

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

avoided because of their additional series inductance. Use

of sockets should also be avoided if possible. Sockets add

parasitic inductance and capacitance that can result in

compromised performance. Minimizing parasitic capacitance

at the amplifier’s inverting input pin is very important. The

feedback resistor should be placed very close to the

inverting input pin. Strip line design techniques are

recommended for the signal traces.

Typical Applications

VIDEO SYNC PULSE REMOVER

Many CMOS analog to digital converters have a parasitic

latch up problem when subjected to negative input voltage

levels. Since the sync tip contains no useful video

information and it is a negative going pulse, we can chop it

off. Figure 29 shows a gain of 2 connections. Figure 30

shows the complete input video signal applied at the input,

as well as the output signal with the negative going sync

pulse removed.

MULTIPLEXER

Besides the normal power down usage, the ENABLE pin of

the EL8200 can be used for multiplexing applications.

Figure 31 shows two channels with the outputs tied together,

driving a back terminated 75

is applied to Amp B. Figure 32 shows the ENABLE signal

break-before-make operation of the multiplexing. Amp A is

ENABLE signal is low and turns off in about 25ns when the

ENABLE signal is high. About 200ns later, Amp B turns on

make operation ensures that more than one amplifier isn’t

trying to drive the bus at the same time.

–

θ

JA

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

=

–

()

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

×

+

×

=

–

() I

LOADi

×

+

×

=

FIGURE 29. SYNC PULSE REMOVER

5V

1K

75

Ω

+

-

75

Ω

1K

75

Ω

EL8200, EL8201, EL8401