+/+…when timing is critical
C9836
Low EMI Clock Generator for Intel Mobile 133MHz/2 SO-DIMM Chipset Systems
Preliminary
Suggested Oscillator Crystal Parameters
Characteristic
Symbol
Min
Typ
Max
Units
MHz
PPM
PPM
Conditions
Frequency
Fo
14.17
14.31818
14.46
Tolerance
TC
-
-
-
-
-
-
-
+/-100
Note 1
Frequency Stability
Operating Mode
Load Capacitance
TS
+/- 100
Stability (TA -10 to +60C) Note 1
Parallel Resonant, Note 1
The crystal’s rated load. Note 1
Note 2
-
-
-
-
-
CXTAL
RESR
20
40
pF
Effective Series
Ohms
Resistance (ESR)
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
= the load rating of the crystal
CXOUTFTG = the clock generators XIN pin effective device internal capacitance to ground
CXOUTFTG = the clock generators XOUT pin effective device internal capacitance to ground
CXINPCB
CXOUTPCB = the effective capacitance to ground of the crystal to device PCB trace
CXINDISC = any discrete capacitance that is placed between the XIN pin and ground
= the effective capacitance to ground of the crystal to device PCB trace
CXOUTDISC = any discrete capacitance that is placed between the XOUT pin and ground
XIN
CXINPCB
CXINDISC
CXINFTG
CXOUTPCB
CXOUTDISC
CXOUTFTG
XOUT
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
(4pF + 36pF + 0pF) + (4pF + 36pF + 0pF) 40 + 40 80
= 20pF
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.
INTERNATIONAL MICROCIRCUITS, INC. 525 LOS COCHES ST.,
MILPITAS, CA 95035, USA TEL: 408-263-6300, FAX 408-263-6571
http://www.imicorp.com
Rev 1.0
3/30/2000
Page 18 of 20
CYPRESS [ CYPRESS ]
