FW802B-DB LSI, FW802B-DB Datasheet - Page 13

• Manufacturer Part Number: FW802B-DB
• Manufacturer: LSI

Specifications of FW802B-DB

• Lead Free Status / Rohs Status: Not Compliant

Data Sheet, Rev. 3
May 2004
Crystal Selection Considerations
Load Capacitance
The frequency of oscillation is dependent upon the load capacitance specified for the crystal, in parallel resonant
mode crystal circuits. Total load capacitance (C
capacitances from the FW802B board traces and capacitances of the other FW802B connected components.
The values for load capacitors (C
C
Where:
C
Cstray = capacitance of the board and the FW802B, typically 2 pF—3 pF
R
Adjustment to Crystal Loading
The resistor (R
dent on the specific crystal used. Please refer to your crystal manufacturer’s data sheet and application notes to
determine an appropriate value for R
values of R
each resistor value. The desired waveform should have the following characteristics: the waveform should be sinu-
soidal, with an amplitude as large as possible, but not greater than 3.3 V or less than 0 volts.
Crystal/Board Layout
The layout of the crystal portion of the PHY circuit is important for obtaining the correct frequency and minimizing
noise introduced into the FW802B PLL. The crystal and two load capacitors (C
unit during layout. They should be placed as close as possible to one another, while minimizing the loop area cre-
ated by the combination of the three components. Minimizing the loop area minimizes the effect of the resonant
current that flows in this resonant circuit. This layout unit (crystal and load capacitors) should then be placed as
close as possible to the PHY XI and XO terminals to minimize trace lengths. Vias should not be used to route the
XI and XO signals.
1394 Application Support Contact Information
E-mail: [e-mail]
Agere Systems Inc.
L
L
A
= load capacitance specified by the crystal manufacturer
= load resistance; the value of R
= C
and application notes to determine an appropriate value.
B
= (C
L
on a production board and using an oscilloscope to view the resultant clock waveform at node A for
L
– C
L)
in Figure 5 is recommended for fine-tuning the crystal circuit. The value for this resistor is depen-
stray
) × 2
L
is dependent on the specific crystal used. Please refer to your crystal manufacturer’s data sheet
A
and C
L
. A more precise value for this resistor can be obtained by placing different
B
XI
XO
) should be calculated using this formula:
Figure 5. Crystal Circuitry
R
(continued)
L
L
) is a function of not only the discrete load capacitors, but also
A
C
C
B
A
FW802B Low-Power PHY IEEE 1394A-2000
Two-Cable Transceiver/Arbiter Device
A
+ C
B
) should be considered as a
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