CDC925

133-MHz CLOCK SYNTHESIZER/DRIVER FOR PC MOTHERBOARDS

WITH 3-STATE OUTPUTS

SCAS633 – JULY 28, 1999

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POST OFFICE BOX 655303

Generate Multiple Output Frequencies

0.34% Downspread for Reduced EMI

Performance

Distribution

– 4 CPU (2.5 V, 100/133 MHz)

– 7 PCI (3.3 V, 33.3 MHz)

– 1 PCI_F (Free Running, 3.3 V, 33.3 MHz)

– 2 CPU/2 (2.5 V, 50/66 MHz)

– 3 APIC (2.5 V, 16.67 MHz)

– 4 3V66 (3.3 V, 66 MHz)

– 2 REF (3.3 V, 14.318 MHz)

– 1 48MHz (3.3 V, 48 MHz)

Clock Generators (CDCR81, CDCR82,

CDCR83)

description

The CDC925 is a clock synthesizer/driver that

generates system clocks necessary to support

Intel Pentium III systems on CPU, CPU_DIV2,

3V66, PCI, APIC, 48MHz, and REF clock signals.

All output frequencies are generated from a

14.318-MHz crystal input. A reference clock input instead of a crystal can be provided at the XIN input. Two

phase-locked loops (PLLs) are used, one to generate the host frequencies and the other to generate the 48-MHz

clock frequency. On-chip loop filters and internal feedback loops eliminate the need for external components.

The host and PCI clock outputs provide low-skew and low-jitter clock signals for reliable clock operation. All

outputs have 3-state capability, which can be selected via control inputs SEL0, SEL1, and SEL133/100.

The outputs are either 3.3-V or 2.5-V single-ended CMOS buffers. With a logic high-level on the PWR_DWN

terminal, the device operates normally, but when a logical low-level input is applied, the device powers down

completely, with the outputs in a low-level output state. When a high-level is applied to the PCI_STOP or

CPU_STOP, the outputs operate normally. With a low-level applied to the PCI_STOP or CPU_STOP terminals,

the PCI or CPU and 3V66 outputs, respectively, are held in a low-level state.

The CPU bus can operate at 100 MHz or 133 MHz. Output frequency selection is done with corresponding

setting for SEL133/100 control input. The PCI bus frequency is fixed to 33MHz.

Copyright

© 1999, Texas Instruments Incorporated

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of Texas Instruments

standard warranty. Production processing does not necessarily include

testing of all parameters.

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GND

REF0

REF1

XIN

XOUT

GND

PCI_F

PCI1

PCI2

PCI3

GND

PCI4

PCI5

PCI6

PCI7

GND

GND

3V66(0)

3V66(1)

GND

3V66(2)

3V66(3)

SEL133/100

APIC2

APIC1

APIC0

GND

CPU_DIV2(1)

CPU_DIV2(0)

GND

CPU3

CPU2

GND

CPU1

CPU0

GND

GND

PCI_STOP

CPU_STOP

PWR_DWN

SPREAD

SEL1

SEL0

48MHz

GND

DL PACKAGE

(TOP VIEW)

Intel and Pentium III are trademarks of Intel Corporation.

Direct Rambus and Rambus are trademarks of Rambus Inc.

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.