EL4332

FN7163 Rev 2.00

Page 8 of 15

October 4, 2004

Applications Information

Figure 26 shows a typical use for the EL4332. The circuit is a

component video (R,G, B or Y,U,V) multiplexer. Since the gain

of the internal amplifiers has been set to 2, the only extra

components needed are the supply decoupling capacitors and

the back terminating resistors, if transmission lines are to be

driven. The EL4332 can drive backmatched 50

 or 75 loads.

Grounds

It will be noticed that each mux-amp channel has its own

separate ground pin. These ground pins have been kept

separate to keep the channel separation inside the chip as

large as possible. The feedback resistors use these ground

pins as their reference. The resistors total 400

, so there is a

significant signal current flowing from these pins to ground.

The ground pins should all be connected together, to a ground

plane underneath the chip. 1 oz. copper for the ground plane is

highly recommended.

Further notes and recommended practices for high speed

printed circuit board layout can be found in the tutorials in the

Elantec databooks.

Supplies

Supply bypassing should be as physically near the power pins

as possible. Chip capacitors should be used to minimize lead

inductance. Note that larger values of capacitor tend to have

larger internal inductances. So when designing for 3

transmission lines or similar moderate loads, a 0.1µF ceramic

capacitor right next to the power pin in parallel with a 22µF

tantalum capacitor placed as close to the 0.1µF is

recommended. For lighter loadings, or if not all the channels

are being used, a single 4.7µF capacitor has been found quite

adequate.

Note that component video signals do tend to have a high level

of signal correlation. This is especially true if the video signal

has been derived from 3 synchronously clocked DACs. This

corresponds to all three channels drawing large slew currents

simultaneously from the supplies. Thus, proper bypassing is

critical.

FIGURE 26. TYPICAL CONNECTION FOR A 2:1 COMPONENT VIDEO MULTIPLEXER