External Reference Sources

An external frequency source may be used as the reference for

the VCLK and MCLK PLLs. To implement this, simply con-

nect the reference frequency source to the XTAL1 pin of the

ICS2572. For best results, insure that the clock edges are as

clean and fast as possible and that the input voltage thresholds

are not violated.

Power Supply

The ICS2572 has two VSS pins to reduce the effects of package

inductance. Both pins are connected to the same potential on

the die (the ground bus). BOTH of these pins should connect

to the ground plane of the video board as close to the package

as is possible.

The ICS2572 has a VDD pin which is the supply of +5 volt

power to all output stages. This pin should be connected to the

power plane (or bus) using standard high-frequency decou-

pling practice. That is, use low-capacitors should have low

series inductance and be mounted close to the ICS2572.

The VAA pin is the power supply for the synthesizer circuitry

and other lower current digital functions. We recommend that

RC decoupling or zener regulation be provided for this pin (as

shown in the recommended application circuitry). This will

allow the PLL to “track” through power supply fluctuations

without visible effects.

ICS2572

E-100