ICS9250-12 Datasheet, PDF (1/12 Pages) Integrated Circuit Systems – Frequency Timing Generator for PENTIUM II/III Systems

Integrated
Circuit
Systems, Inc.
ICS9250-12
Frequency Timing Generator for PENTIUM II/III Systems
General Description
The ICS9250-12 is a main clock synthesizer chip for
Pentium II based systems using Rambus Interface DRAMs.
This chip provides all the clocks required for such a system
when used with a Direct Rambus Clock Generator (DRCG)
chip such as the ICS9212-01, 02, 03 and a PCI buffer 9112-17.
Spread Spectrum may be enabled by driving the SPREAD#
pin active. Spread spectrum typically reduces system EMI
by 8dB to 10dB. This simplifies EMI qualification without
resorting to board design iterations or costly shielding. The
ICS9250-12 employs a proprietary closed loop design,
which tightly controls the percentage of spreading over
process and temperature variations.
The CPU/2 clocks are inputs to the DRCG.
Key Specification:
• CPU Output Jitter: 150ps
• IOAPIC Output Jitter: 250ps
• CPU/2, 3V66, PCI Output Jitter: 250ps
• CPU (0:3) CPU/2 Output Skew: <175ps
• PCI_F, PCI 1:7 Output Skew: <500ps
• 3V66 (0:3) Output Skew <250ps
• IOAPIC (0:2) Output Skew <250ps
• CPU to 3V66 (0:3) Output Offset: 0.0 - 1.5ns (CPU leads)
• CPU to PCI Output Offset: 1.5 - 4.0ns (CPU leads)
• CPU to APIC Output Offset 1.5 - 4.0ns (CPU leads)
Features
• Generates the following system clocks:
- 4 CPU clocks ( 2.5V, 100/133MHz)
- 8 PCI clocks, including 1 free-running (3.3V, 33MHz)
- 2 CPU/2 clocks (2.5V, 50/66MHz)
- 3 IOAPIC clocks (2.5V, 16.67MHz)
- 4 Fixed frequency 66MHz clocks(3.3V, 66MHz)
- 2 REF clocks(3.3V, 14.318MHz)
- 1 USB clock (3.3V, 48MHz)
• Efficient power management through PD#, CPU_STOP#
and PCI_STOP#.
• 0.5% typical down spread modulation on CPU, PCI,
IOAPIC, 3V66 and CPU/2 output clocks.
• Uses external 14.318MHz crystal.
Pin Configuration
Block Diagram
9250-12 Rev B 2/23/00
56-pin SSOP
ICS reserves the right to make changes in the device data identified in
this publication without further notice. ICS advises its customers to
obtain the latest version of all device data to verify that any
information being relied upon by the customer is current and accurate.