参数资料
型号: C9530CT
英文描述: ST7262 - LOW SPEED USB 8-BIT MCU WITH 3 ENDPOINTS, FLASH OR ROM MEMORY, LVD, WDG, 10-BIT ADC, 2 TIMERS, SCI, SPI
中文描述: CPU系统时钟发生器|的CMOS | TSSOP封装| 48PIN |塑料
文件页数: 11/14页
文件大小: 180K
代理商: C9530CT
PCIX I/O System Clock Generator With EMI Control Features
Cypress Semiconductor Corporation
525 Los Coches St.
Milpitas, CA 95035. Tel: 408-263-6300, Fax: 408-263-6571
http://www.cypress.com
Document#: 38-07033 Rev. **
5/1/2000
Page 11 of 14
APPROVED PRODUCT
C9530
Suggested Oscillator Crystal Parameters (Cont.)
The following formula and schematic may be used to understand and calculate either the loading specification of a
crystal for a design or the additional discrete load capacitance that must be used to provide the correct load to a
known load rated crystal.
C
L
= (C
XINPCB
+ C
XINFTG
+ C
XINDISC
) X (C
XOUTPCB
+ C
XOUTFTG
+ C
XOUTDISC
)
(C
XINPCB
+ C
XINFTG
+ C
XINDISC
) + (C
XOUTPCB
+ C
XOUTFTG
+ C
OUTDISC
)
Where:
C
XTAL
C
XOUTFTG
= the clock generators XIN pin effective device internal capacitance to ground
C
XOUTFTG
= the clock generators XOUT pin effective device internal capacitance to ground
C
XINPCB
= the effective capacitance to ground of the crystal to device PCB trace
C
XOUTPCB
= the effective capacitance to ground of the crystal to device PCB trace
C
XINDISC
= any discrete capacitance that is placed between the XIN pin and ground
C
XOUTDISC
= any discrete capacitance that is placed between the XOUT pin and ground
= the load rating of the crystal
C
XINPCB
C
XOUTPCB
C
XOUTDISC
C
XINDISC
C
XINFTG
C
XOUTFTG
XIN
XOUT
Clock Generator
As an example, and using this formula for this datasheet’s device, a design that has no discrete loading capacitors
(C
DISC
) and each of the crystal to device PCB traces has a capacitance (C
PCB
) to ground of 4pF (typical value)
would calculate as:
C
L
= (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.
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