ICS84025 Datasheet, PDF (7/12 Pages) Integrated Circuit Systems – CRYSTAL-TO-LVCMOS / LVTTL FREQUENCY SYNTHESIZER WITH FANOUT BUFFER

Integrated
Circuit
Systems, Inc.
PRELIMINARY
ICS84025
CRYSTAL-TO-LVCMOS / LVTTL
FREQUENCY SYNTHESIZER WITH FANOUT BUFFER
APPLICATION INFORMATION
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. The ICS84025 provides sepa-
rate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V_DD, V_DDA, and V_DDO
should be individually connected to the power supply
plane through vias, and bypass capacitors should be
used for each pin. To achieve optimum jitter performance,
power supply isolation is required. Figure 2 illustrates how
a 24Ω resistor along with a 10µF and a .01µF bypass
capacitor should be connected to each V_DDA pin.
V_DD
V
DDA
3.3V
.01µF 24 Ω
.01µF
10 µF
FIGURE 2. POWER SUPPLY FILTERING
CRYSTAL INPUT INTERFACE
A crystal can be characterized for either series or parallel
mode operation. The ICS84025 has a built-in crystal oscillator
circuit. This interface can accept either a series or parallel
crystal without additional components and generate
frequencies with accuracy suitable for most applications.
Additional accuracy can be achieved by adding two small
capacitors C1 and C2 as shown in Figure 3.
25MHz X1
20
C1
18pF
XTAL2
21
C2
22pF
XTAL1
ICS84025
Figure 3. CRYSTAL INPUt INTERFACE
84025EM
www.icst.com/products/hiperclocks.html
7
REV. A APRIL 16, 2003