TEXAS INSTRUMENTS CDC924 Technical data

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CDC924

133-MHz CLOCK SYNTHESIZER/DRIVER FOR PC MOTHERBOARDS

WITH 3-STATE OUTPUTS

SCAS607A – NOVEMBER 1998 – REVISED MA Y 1999

D

Supports Pentium III Class Motherboards

D

Uses a 14.318-MHz Crystal Input to
Generate Multiple Output Frequencies

D

Includes Spread Spectrum Clocking (SSC),

0.5% Downspread for Reduced EMI
Performance

D

Power Management Control Terminals

D

Low Output Skew and Jitter for Clock
Distribution

D

2.5-V and 3.3-V Supplies

D

Generates the Following Clocks:
– 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)

D

Packaged in 56-Pin SSOP Package

D

Designed for Use with TI’s Direct Rambus
Clock Generators (CDCR81, CDCR82,
CDCR83)

description

The CDC924 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.

GND
REF0
REF1

3.3V

V

DD

XIN

XOUT

GND

PCI_F

PCI1

VDD3.3V

PCI2

PCI3

GND

PCI4

PCI5

VDD3.3V

PCI6

PCI7

GND

GND

3V66(0)
3V66(1)

3.3V

V

DD

GND

3V66(2)
3V66(3)

V

3.3V

DD

SEL133/100

DL PACKAGE

(TOP VIEW)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28

56

VDD2.5V

55

APIC2

54

APIC1

53

APIC0

52

GND

51

V

50

CPU_DIV2(1)

49

CPU_DIV2(0)

48

GND

47

V

46

CPU3

45

CPU2

44

GND

43

V

42

CPU1

41

CPU0

40

GND

39

V

38

GND

37

PCI_STOP

36

CPU_STOP

35

PWR_DWN

34

SPREAD

33

SEL1

32

SEL0

31

V

30

48MHz

29

GND

DD

DD

DD

DD

DD

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.

2.5V

2.5V

2.5V

3.3V

3.3V

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
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

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.

Intel and Pentium III are trademarks of Intel Corporation.
Direct Rambus and Rambus are trademarks of Rambus Inc.

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.

control input. The PCI bus frequency is fixed to 33MHz.

Copyright  1999, Texas Instruments Incorporated

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

.

or

1

CDC924
133-MHz CLOCK SYNTHESIZER/DRIVER FOR PC MOTHERBOARDS
WITH 3-STATE OUTPUTS

SCAS607A – NOVEMBER 1998 – REVISED MA Y 1999

description (continued)

Since the CDC924 is based on PLL circuitry, it requires a stabilization time to achieve phase lock of the PLL.
This stabilization time is required after power up or after changes to the SEL inputs are made. With use of an
external reference clock, this signal must be fixed-frequency and fixed-phase before the stabilization time starts.

function tables

SELECT FUNCTIONS

INPUTS

SEL133/

100

SEL1 SEL0 CPU CPU_DIV2 3V66

L L L Hi-Z Hi-Z Hi-Z Hi-Z Hi-Z Hi-Z Hi-Z 3-state
L L H N/A N/A N/A N/A N/A N/A N/A Reserved
L H L 100 MHz 50 MHz 66 MHz 33 MHz Hi-Z 14.318 MHz 16.67 MHz 48-MHz PLL off
L H H 100 MHz 50 MHz 66 MHz 33 MHz 48 MHz 14.318 MHz 16.67 MHz 48-MHz PLL on

H L L TCLK/2 TCLK/4 TCLK/4 TCLK/8 TCLK/2 TCLK TCLK/16 Test
H L H N/A N/A N/A N/A N/A N/A N/A Reserved

H H L 133 MHz 66 MHz 66 MHz 33 MHz Hi-Z 14.318 MHz 16.67 MHz 48-MHz PLL off
H H H 133 MHz 66 MHz 66 MHz 33 MHz 48 MHz 14.318 MHz 16.67 MHz 48-MHz PLL on

OUTPUTS

PCI,

PCI_F

48MHz REF APIC

FUNCTION

ENABLE FUNCTIONS

INPUTS

CPU_STOP PWR_DWN PCI_STOP CPU CPU_DIV2 APIC 3V66 PCI PCI_F

X L X L L L L L L L Of f Off

L HLLOn On L L On On On On

L HHLOn On L On On On On On
H HLOnOn On On L On On On On
H H H On On On On On On On On On

OUTPUT BUFFER SPECIFICATIONS

BUFFER NAME

CPU, CPU_DIV2, APIC 2.375 – 2.625 13.5 – 45 TYPE 1

48MHz, REF 3.135 – 3.465 20 – 60 TYPE 3

PCI, PCI_F, 3V66 3.135 – 3.465 12 – 55 TYPE 5

VDD RANGE

(V)

OUTPUTS INTERNAL

IMPEDANCE

(Ω)

REF,

48MHz

BUFFER TYPE

Crystal VCOs

2

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I/O

DESCRIPTION

133-MHz CLOCK SYNTHESIZER/DRIVER FOR PC MOTHERBOARDS

SCAS607A – NOVEMBER 1998 – REVISED MA Y 1999

Terminal Functions

TERMINAL

NAME NO.

3V66 [0–3] 21, 22, 25, 26 O 3.3 V, Type 5, 66-MHz clock outputs

48MHz 30 O 3.3 V, Type 3, 48-MHz clock output

APIC [0–2] 53, 54, 55 O 2.5 V, T ype 1, APIC clock outputs

CPU [0–3] 41, 42, 45, 46 O 2.5 V, Type 1, CPU clock outputs

CPU_DIV2 [0–1] 49, 50 O 2.5 V, Type 1, CPU_DIV2 clock outputs

CPU_STOP 36 I Disables CPU clock to low state

GND 1, 7, 13, 19,

20, 24, 29, 38,

40, 44, 48, 52

PCI [1–7] 9, 11, 12, 14,

15, 17, 18
PCI_F 8 O Free-running 3.3-V, Type 5, 33-MHz PCI clock output
PCI_STOP 37 I Disables PCI clock to low state
PWR_DWN 35 I Power down for complete device with outputs forced low
REF0, REF1 2, 3 O 3.3 V, Type 3, 14.318-MHz reference clock output
SEL0, SEL1 32, 33 I LVTTL level logic select terminals for function selection
SEL133/100 28 I LVTTL level logic select pins for enabling 100/133 MHz
SPREAD 34 I Disables SSC function
VDD3.3V 4, 10, 16, 23,

27, 31, 39
VDD2.5V 43, 47, 51, 56 Power for CPU and APIC outputs
XIN 5 I Crystal input – 14.318 MHz
XOUT 6 O Crystal output – 14.318 MHz

O 3.3 V, Type 5, 33-MHz PCI clock outputs

Ground

Power for the 3V66, 48MHz, PCI, REF outputs and CORE logic

CDC924

WITH 3-STATE OUTPUTS

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

3

CDC924
133-MHz CLOCK SYNTHESIZER/DRIVER FOR PC MOTHERBOARDS
WITH 3-STATE OUTPUTS

SCAS607A – NOVEMBER 1998 – REVISED MA Y 1999

spread spectrum clock (SSC) implementation for CDC924

Simultaneously switching at fixed frequency generates a significant power peak at the selected frequency,
which in turn will cause EMI disturbance to the environment. The purpose of the internal frequency modulation
of the CPU–PLL allows to distribute the energy to many different frequencies which reduces the power peak.
A typical characteristic for a single frequency spectrum and a frequency modulated spectrum is shown in
Figure 1.

Highest Peak

SSC

δ of f

nom

∆

Non-SSC

f

nom

Figure 1. Frequency Power Spectrum With and Without the Use of SSC

The modulated spectrum has its distribution left hand to the single frequency spectrum which indicates a
“down-spread modulation”.

The peak reduction depends on the modulation scheme and modulation profile. System performance and timing
requirements are the limiting factors for actual design implementations. The implementation was driven to keep
the average clock frequency closed to its upper specification limit. The modulation amount was set to
approximately –0.5%.

In order to allow a downstream PLL to follow the frequency modulated signal, the bandwidth of the modulation
signal is limited in order to minimize SSC induced tracking skew jitter. The ideal modulation profile used for
CDC924 is shown in Figure 2.

10.03

10.02

10.01
10

9.99

9.98

9.97

Period of Output Frequency – ns

51015202530354045

Period of Modulation Signal – µs

Figure 2. SSC Modulation Profile

4

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functional block diagram

CDC924

133-MHz CLOCK SYNTHESIZER/DRIVER FOR PC MOTHERBOARDS

WITH 3-STATE OUTPUTS

SCAS607A – NOVEMBER 1998 – REVISED MA Y 1999

SEL133/100

SEL0

SEL1

XIN

XOUT

CPU_STOP

SPREAD

28

32

33

5
6

36

34

Xtal

Oscillator

Control

Logic

Spread

Logic

3–State

48–MHz Inactive

Test

SEL133/100

CPU

PLL

48 MHz

PLL

/3

/4

/2 /2

STOP

STOP

2*REF

14.318 MHz
(2,3)

1*48MHz
48 MHz
(30)

4*AGP (3V66)
66 MHz
(21,22,25,26)

4*CPU
100/133 MHz
(41,42,45,46)

2*CPU_DIV2
50/66 MHz

Sync Logic & Power Down Logic

(49,50)

PCI_STOP

PWR_DOWN

37

35

3*APIC

16.67 MHz

/3

/4

STOP

/2

(53, 54, 55)
1*PCI_F

33 MHz
(8)

7*PCI
33 MHz
(9,11,12,14,
15,17,18)

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5

CDC924

†

PACKAGE

A

A

A

Suppl

oltage, V

V

High-level output current, I

mA

Low-level output current, I

mA

133-MHz CLOCK SYNTHESIZER/DRIVER FOR PC MOTHERBOARDS
WITH 3-STATE OUTPUTS

SCAS607A – NOVEMBER 1998 – REVISED MA Y 1999

absolute maximum ratings over operating free-air temperature range (unless otherwise noted)

Supply voltage range, V
Input voltage range, V
Voltage range applied to any output in the high-impedance state or power-off state,

V

(see Note 1) –0.5 V to VDD + 0.5 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

O

Current into any output in the low state, I
Input clamp current, I
Output clamp current, I
Operating free-air temperature range, T
Storage temperature range, T

Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds 260°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

†

Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

NOTE 1: The input and output negative-voltage ratings may be exceeded if the input and output clamp-current ratings are observed.

DL 1558.6 mW 12.468 mW/°C 997.5 mW 810.52 mW

†

This is the inverse of the traditional junction-to-case thermal resistance (R
at 80.2°C/W.

–0.5 V to 4.6 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DD

(see Note 1) –0.5 V to 4.6 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

I

2 × I

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(V

< 0) –18 mA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

IK

I

(V

< 0) –50 mA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

OK

POWER RATNG ABOVE TA = 25°C

O

–65°C to 150°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

stg

T

≤ 25°C DERATING FACT OR

O

–0°C to 85°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A

DISSIPATION RATING TABLE

T

= 70°C T

POWER RATING

) and uses a board-mounted device

θJA

= 85°C

POWER RATING

recommended operating conditions (see Note 2)

MIN NOM

pp

y v

High-level input voltage, V

Low-level input voltage, V
Input voltage, V

Reference frequency, f
Crystal frequency, f
Operating free-air temperature, T

NOTE 2: Unused inputs must be held high or low to prevent them from floating.
†

All nominal values are measured at their respective nominal VDD values.

‡

Reference frequency is a test clock driven on the XIN input during the device test mode and normal mode. In test mode, XIN can be driven
externally up to f

§

This is a series fundamental crystal with fO = 14.31818 MHz.

DD

IH

IL

I

p

p

(XIN)

OH

OL

‡

(XIN)

§

(XTAL)

A

= 130 MHz. If XIN is driven externally, XOUT is floating.

3.3 V 3.135 3.465

2.5 V 2.375 2.625
2

GND –

0.3 V
0 V

CPUx, CPU_DIV2x –12
APICx –12
48MHz, REFx –14
PCIx, PCI_F, 3V66x –18
CPUx, CPU_DIV2x 12
APICx 12
48MHz, REFx 9
PCIx, PCI_F, 3V66x 12
Test mode 130 MHz
Normal mode 13.8 14.318 14.8 MHz

0 85 °C

†

VDD +

MAX UNIT

0.3 V

0.8 V

DD

V

V

†

OL

6

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265