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ICS9250-11

Frequency Timing Generator for PENTIUM II/III™ Systems

Integrated Circuit Systems 

Integrated

Circuit

Systems, Inc.

ICS9250-11

Frequency Timing Generator for PENTIUM II/III™ Systems

General Description

The ICS9250-11 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

ICS9250-11 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.

Block Diagram

Features

• Generates the following system clocks:

- 6 - CPU Clocks 100/133MHz (2.5V).

- 2 - CPU/2 output for synchronous memory

reference (2.5V).

- 4 - fixed frequency Clocks @ 66.6MHz (3.3V).

- 2 - fixed frequency Clocks @ 33.3MHz (3.3V).

- 6 - IOAPIC Clocks @ ¼ of CPUCLK or 16.667MHz,

synchronous to CPU Clock (2.5V)

- 1 - 48MHz Clock (3.3V)

- 2 - REF Clocks @ 14.31818MHz

• 0.5% typical down spread modulation on CPU, PCI,

IOAPIC, 3V66 and CPU/2 output clocks.

• Uses external 14.318MHz crystal.

X1

X2

SPREAD#

OSC

PLL

Spread

/2

Spectrum

C

o

SEL 133/100#

n

SEL(0:1)

t

r

o

l

/3 /2

PLL2

/3

/4

/2

/2

/2

2 REF (0:1)

CPUCLK (0:5)

6

6 IOAPIC(0:5)

2 CPU/2 (0:1)

4 3V66 (0:3)

2 3V33 (0:1)

48MHz

Pin Configuration

Power Groups:

VDDREF, GNDREF = REF, X1, X2

VDD66, GND66 = 3V66

VDD33, GND33 = 3V33

VDD48, GND48 = 48MHz

VDDCOR, GNDCOR = PLL Core

VDDLCPU, GNDLCPU = CPUCLK

VDDLCPU/2 , GNDLCPU/2 = CPU/2

VDDLAPIC, GNDAPIC = IOAPIC

9250-11 Rev C 3/20/00

Third party brands and names are the property of their respective owners.

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.

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