C9851 Datasheet, PDF (11/14 Pages) Cypress Semiconductor – Clock Generator for Pentium III Server and Workstation Applications

PRELIMINARY
C9851
Clock Generator for Pentium^III Server and Workstation Applications
Suggested Oscillator Crystal Parameters
Characteristic
Symbol
Min
Typ
Max
Units Conditions
Frequency
Fo
14.17
14.31818
14.46
MHz
Tolerance
TC
-
-
+/-100
PPM Note 1
Frequency Stability
TS
-
-
+/- 100
PPM Stability (TA -10 to +60C) Note 1
Operating Mode
-
-
-
-
Parallel Resonant, Note 1
Load Capacitance
CXTAL
-
20
-
pF
The crystal’s rated load. Note 1
Effective Series
RESR
-
40
Resistance (ESR)
-
Ohms Note 2
Note1: For best performance and accurate frequencies from this device, It is recommended but not mandatory that the chosen
crystal meets or exceeds these specifications
Note 2: Larger values may cause this device to exhibit oscillator startup problems
To obtain the maximum accuracy, the total circuit loading capacitance should be equal to CXTAL. This loading capacitance is the
effective capacitance across the crystal pins and includes the clock generating device pin capacitance (CFTG), any circuit trace
capacitance (CPCB), and any onboard discrete load capacitance (CDISC).
The following formula and schematic illustrates the application of the loading specification of a crystal (CXTAL)for a design.
CL = (CXINPCB + CXINFTG + CXINDISC) X (CXOUTPCB + CXOUTFTG + CXOUTDISC)
(CXINPCB + CXINFTG + CXINDISC) + (CXOUTPCB + CXOUTFTG + COUTDISC)
Where:
CXTAL
CXOUTFTG
CXOUTFTG
CXINPCB
CXOUTPCB
CXINDISC
CXOUTDISC
= the load rating of the crystal
= the clock generators XIN pin effective device internal capacitance to ground
= the clock generators XOUT pin effective device internal capacitance to ground
= the effective capacitance to ground of the crystal to device PCB trace
= the effective capacitance to ground of the crystal to device PCB trace
= any discrete capacitance that is placed between the XIN pin and ground
= any discrete capacitance that is placed between the XOUT pin and ground
C_XINPCB
C_XINDISC
XIN
C_XINFTG
C_XOUTPCB
C_XOUTDISC
XOUT ^CXOUTFTG
Clock Generator
As an example, and using this formula for this datasheet’s device, a design that has no discrete loading capacitors (CDISC) and each
of the crystal to device PCB traces has a capacitance (CPCB) to ground of 4pF (typical value) would calculate as:
CL = (4pF + 36pF + 0pF) X (4pF + 36pF + 0pF) = 40 X 40 = 1600 = 20pF
(4pF + 36pF + 0pF) + (4pF + 36pF + 0pF) 40 + 40
80
Therefore to obtain output frequencies that are as close to this data sheets specified values as possible, in this design
example, you should specify a parallel cut crystal that is designed to work into a load of 20pF
Cypress Semiconductor Corporation
525 Los Coches St.
Milpitas, CA 95035. Tel: [phone], Fax: [phone]
http://www.cypress.com
Document#: 38-07068 Rev. **
05/04/2001
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