L-USS820FD-DB AGERE [Agere Systems], L-USS820FD-DB Datasheet - Page 50

• Manufacturer Part Number: L-USS820FD-DB
• Description: USB Device Controller
• Manufacturer: AGERE [Agere Systems]

USS-820FD
USB Device Controller
USB Device Controller
Electrical Characteristics
Connection Requirements
Oscillator Connection Requirements
The USS-820FD 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 10 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 11 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 47.
Table 47. Clock Characteristics
* Duty cycle applies to any frequency in an specified range.
50
External Clock Source Frequency
Clock Period
Clock Duty Cycle*
Oscillator Stable Time
Parameter
(continued)
(continued)
Figure 11. External Oscillator Source
Figure 10. Internal Oscillator Mode
OSCILLATOR
12 MHz
Symbol
t
CL
t
t
OSC
CYC
, t
f
CH
XTAL2
XTAL1
XTAL2
XTAL1
11.976
83.1
Min
40
—
12.000
83.3
Typ
50
—
Data Sheet, Rev. 1
Agere Systems Inc.
12.024
Max
83.5
60
August 2004
7
Unit
MHz
ms
ns
%
5-5405.a
5-5406.a