參數(shù)資料
型號: USS-820D
英文描述: USS-820D USB Device Controller
中文描述: 號- 820D USB設(shè)備控制器
文件頁數(shù): 51/58頁
文件大?。?/td> 868K
代理商: USS-820D
Agere Systems Inc.
51
Data Sheet, Rev. 4
June 2001
USB Device Controller
USS-820D
Electrical Characteristics
(continued)
Connection Requirements
(continued)
Oscillator Connection Requirements
The USS-820D requires an internal 48 MHz clock that it creates from an internal 12 MHz clock via a 4X PLL. Two
methods of clock generation may be used to create this internal 12 MHz clock. Figure 11 shows the internal oscil-
lator mode which requires only an external 12 MHz crystal and bias capacitors. The values of the capacitors
should be chosen as indicated by the crystal manufacturer in order to cause the crystal to operate in a parallel
resonant condition. A typical value is 15 pF, but the required value may differ, depending on the specific crystal and
board characteristics of the application.
Alternatively, Figure 12 shows the configuration required to input a 12 MHz clock from an external oscillator. In
either configuration, the external clock source must have the characteristics defined in Table 46.
5-5405.a
Figure 11. Internal Oscillator Mode
5-5406.a
Figure 12. External Oscillator Source
Table 46. Clock Characteristics
* Duty cycle applies to any frequency in an specified range.
Parameter
Symbol
f
t
CYC
t
CL
, t
CH
t
OSC
Min
11.976
83.1
40
Typ
12.000
83.3
50
Max
12.024
83.5
60
7
Unit
MHz
ns
%
ms
External Clock Source Frequency
Clock Period
Clock Duty Cycle*
Oscillator Stable Time
XTAL2
XTAL1
XTAL2
XTAL1
12 MHz
OSCILLATOR
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