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IDT54FCT388915T70PYB

3.3V LOW SKEW PLL-BASED CMOS CLOCK DRIVER WITH (3-STATE)

Integrated Device Technology 

IDT54/74FCT388915T 70/100/133/150

3.3V LOW SKEW PLL-BASED CLOCK DRIVER

BOARD VCC

MILITARY AND COMMERCIAL TEMPERATURE RANGES

10µF

Low

Freq.

Bypass

0.1µF

High

Freq.

Bypass

ANALOG VCC

0.1µF (Loop

Filter Cap)

Analog loop filter

LF

section of the

FCT388915T

ANALOG GND

BOARD GND

A separate Analog power supply

is not necessary and should not

be used. Following these

prescribed guidelines is all that is

necessary to use the FCT388915

in a normal digital environment.

3052 drw 12

Figure 2. Recommended Loop Filter and Analog Isolation Scheme for the FCT388915T

NOTES:

1. Figure 2 shows a loop filter and analog isolation scheme which will be effective in most applications. The following guidelines should be followed to ensure

stable and jitter-free operation:

a. All loop filter and analog isolation components should be tied as close to the package as possible. Stray current passing through the parasitics of

long traces can cause undesirable voltage transients at the LF pin.

b. The 10µF low frequency bypass capacitor and the 0.1µF high frequency bypass capacitor form a wide bandwidth filter that will minimize the

388915T's sensitivity to voltage transients from the system digital VCC supply and ground planes.

If good bypass techniques are used on a board design near components which may cause digital VCC and ground noise, VCC step deviations should

not occur at the 388915T's digital VCC supply. The purpose of the bypass filtering scheme shown in figure 2 is to give the 388915T additional

protection from the power supply and ground plane transients that can occur in a high frequency, high speed digital system.

c. The loop filter capacitor (0.1µF) can be a ceramic chip capacitor, the same as a standard bypass capacitor.

2. In addition to the bypass capacitors used in the analog filter of figure 2 there should be a 0.1µF bypass capacitor between each of the other (digital) four

VCC pins and the board ground plane. This will reduce output switching noise caused by the 388915T outputs, in addition to reducing potential for noise

in the "analog" section of the chip. These bypass capacitors should also be tied as close to the 388915T package as possible.

9.8

7

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