11525-801 View Datasheet(PDF) - AMI Semiconductor
Part Name
Description
Manufacturer
11525-801 Datasheet PDF : 26 Pages
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April 1999
1.0 Features
• Generates clocks required for Intel Pentium® II based
systems, including:
♦ Four enabled 2.5V 100MHz or 66MHz CPU sys-
tem bus clock outputs
♦ Seven enabled 3.3V PCI bus clocks and one
free-running PCI clock
♦ Three 3.3V REF clocks at 14.318MHz
♦ Two 2.5V APIC clocks at 14.318MHz for APIC
bus timing
♦ Two 3.3V 48MHz clocks for 4x Universal Serial
Bus (USB) timing
• Non-linear spread spectrum modulation (-0.5% at
31.5kHz)
• Selectable 100MHz or 66MHz system bus clock
• Supports Intel Test Mode and tristate output control
to facilitate board testing
• Synchronous clocks skew-matched to <175ps on
CPU and APIC buffers and <250ps on PCI buffers
• Separate CPU-enable, PCI-enable and power-down
inputs with glitch-free stop clock controls on all clocks
for clock control and power management
• All inputs and 3.3V outputs are LVTTL-compatible
2.0 Description
The FS6251-01 is a CMOS clock generator IC designed
for high-speed motherboard applications. Two different
frequencies can be selected for the CPU and PCI clocks
via two SEL pins. Glitch-free stop clock control of the
CPU and PCI clocks is provided. A low current power-
down mode is available for mobile applications. Separate
clock buffers provide for a 2.5V voltage range on the
CPU_0:3 and APIC_0:1 clocks.
Figure 2: Pin Configuration (FS6251)
(2.5V outputs)
FS6251-01
48-pin SSOP
Figure 2: Pin Configuration (FS6252)
(2.5V outputs)
Figure 1: Block Diagram (FS6251)
XIN
XOUT
CPU_STOP#
SEL_0:1
SEL_100/66#
PCI_STOP#
SS_EN#
PWR_DWN#
Crystal
Oscillator
PLL
PLL
÷2 or
÷3
÷2
delay
VDD_R
REF_0:2
VSS_R
VDD_A
APIC_0:1
VSS_A
VDD_C
CPU_0:3
VSS_C
(2.5V outputs)
VDD_P
PCI_F
PCI_1:7
VSS_P
VDD_U
48M_0:1
VSS_U
FS6251-01
FS6252-01
28-pin SSOP, SOIC
Table 1: CPU/PCI Frequency Selection
SEL_100/66#
0
0
0
0
1
1
1
1
SEL_1
0
0
1
1
0
0
1
1
SEL_0
0
1
0
1
0
1
0
1
CPU (MHz)
tristate
70
73.33
66.67
XIN/2
105
110
100
PCI (MHz)
tristate
35
36.67
33.33
XIN/6
35
36.67
33.33
Intel and Pentium are registered trademarks of Intel Corporation. Lexmark is a trademark of Lexmark International, Inc. Spread spectrum modulation is licensed under US Patent No. 5488627,
Lexmark International, Inc. American Microsystems, Inc. reserves the right to change the detail specifications as may be required to permit improvements in the design of its products.
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4.5.99
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