74FCT388915TDJG IDT, 74FCT388915TDJG Datasheet - Page 6

• Manufacturer Part Number: 74FCT388915TDJG
• Description: Clock Drivers & Distribution
• Manufacturer: IDT

Specifications of 74FCT388915TDJG

• Product Category: Clock Drivers & Distribution
• Rohs: yes
• Part # Aliases: IDT74FCT388915TDJG

GENERAL AC SPECIFICATION NOTES (continued):
8. The tPD spec describes how the phase offset between the SYNC input and the output connected to the FEEDBACK input, varies with process, temperature and voltage. The
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
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 V
IDT74FCT388915T
3.3V LOW SKEW PLL-BASED CMOS CLOCK DRIVER (3-STATE)
phase measurements were made at 1.5V. The Q/2 output was terminated at the FEEDBACK input with 100Ω to V
the loop filter connection shown in Figure 1 below:
operation:
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.
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
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
c. The loop filter capacitor (0.1µF) can be a ceramic chip capacitor, the same as a standard bypass capacitor.
digital V
that can occur in a high frequency, high speed digital system.
voltage transients at the LF pin.
transients from the system digital V
If good bypass techniques are used on a board design near components which may cause digital V
CC
10
Low
Freq.
Bypass
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
μ
F
0.1
High
Freq.
Bypass
Figure 2. Recommended Loop Filter and Analog Isolation Scheme for the FCT388915T
μ
F
CC
supply and ground planes.
BOARD V
BOARD GND
External Loop
Filter
0.1
Filter Cap)
CC
μ
F (Loop
Figure 1
0.1
A separate Analog power supply is not necessary
and should not be used. Following these pre-
scribed guidelines is all that is necessary to use
the FCT388915T in a normal digital environm ent.
μ
6
F
LF
Analog GND
C 1
CC
and ground noise, V
ANALOG V
LF
ANALOG GND
CC
Analog loop filter section
of the FCT388915T
and 100Ω to ground. tPD measurements were made with
CC
CC
COMMERCIAL TEMPERATURE RANGE
step deviations should not occur at the 388915T's
CC
pins and the board