Texas Instruments CDC925DLR, CDC925DL Datasheet
CDC925
133-MHz CLOCK SYNTHESIZER/DRIVER FOR PC MOTHERBOARDS
WITH 3-STATE OUTPUTS
SCAS633 – JUL Y 28, 1999
1
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
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),
0.34% 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 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.
1
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5
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7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
56
55
54
53
52
51
50
49
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
GND
REF0
REF1
V
DD
3.3V
XIN
XOUT
GND
PCI_F
PCI1
V
DD
3.3V
PCI2
PCI3
GND
PCI4
PCI5
V
DD
3.3V
PCI6
PCI7
GND
GND
3V66(0)
3V66(1)
V
DD
3.3V
GND
3V66(2)
3V66(3)
V
DD
3.3V
SEL133/100
VDD2.5V
APIC2
APIC1
APIC0
GND
V
DD
2.5V
CPU_DIV2(1)
CPU_DIV2(0)
GND
V
DD
2.5V
CPU3
CPU2
GND
V
DD
2.5V
CPU1
CPU0
GND
V
DD
3.3V
GND
PCI_STOP
CPU_STOP
PWR_DWN
SPREAD
SEL1
SEL0
V
DD
3.3V
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.
CDC925
133-MHz CLOCK SYNTHESIZER/DRIVER FOR PC MOTHERBOARDS
WITH 3-STATE OUTPUTS
SCAS633 – JUL Y 28, 1999
2
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
description (continued)
Since the CDC925 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
OUTPUTS
SEL133/
100
SEL1 SEL0 CPU CPU_DIV2 3V66
PCI,
PCI_F
48MHz REF APIC
FUNCTION
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
ENABLE FUNCTIONS
INPUTS
OUTPUTS INTERNAL
CPU_STOP PWR_DWN PCI_STOP CPU CPU_DIV2 APIC 3V66 PCI PCI_F
REF,
48MHz
Crystal VCOs
X L X L L L L L L L Off 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
VDD RANGE
(V)
IMPEDANCE
(Ω)
BUFFER TYPE
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
CDC925
133-MHz CLOCK SYNTHESIZER/DRIVER FOR PC MOTHERBOARDS
WITH 3-STATE OUTPUTS
SCAS633 – JUL Y 28, 1999
3
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
Terminal Functions
TERMINAL
NAME NO.
I/O
DESCRIPTION
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, Type 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
Ground
PCI [1–7] 9, 11, 12, 14,
15, 17, 18
O 3.3 V, Type 5, 33-MHz PCI clock outputs
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
Power for the 3V66, 48MHz, PCI, REF outputs and CORE logic
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
CDC925
133-MHz CLOCK SYNTHESIZER/DRIVER FOR PC MOTHERBOARDS
WITH 3-STATE OUTPUTS
SCAS633 – JUL Y 28, 1999
4
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
spread spectrum clock (SSC) implementation for CDC925
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
Non-SSC
SSC
δ of f
nom
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 –0.34% (compared to –0.5% on the CDC924).
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
CDC925 is shown in Figure 2.
51015202530354045
Period of Modulation Signal – µs
9.97
9.98
9.99
10
10.01
10.02
10.03
Period of Output Frequency – ns
Figure 2. SSC Modulation Profile
CDC925
133-MHz CLOCK SYNTHESIZER/DRIVER FOR PC MOTHERBOARDS
WITH 3-STATE OUTPUTS
SCAS633 – JUL Y 28, 1999
5
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
functional block diagram
2*REF
14.318 MHz
(2,3)
SEL133/100
PWR_DOWN
PCI_STOP
SPREAD
XOUT
XIN
SEL1
SEL0
Control
Logic
28
33
32
3–State
Test
48–MHz Inactive
SEL133/100
Xtal
Oscillator
6
5
48 MHz
PLL
CPU
PLL
Spread
Logic
Sync Logic & Power Down Logic
/2 /2
34
37
36
35
1*48MHz
48 MHz
(30)
3*APIC
16.67 MHz
(53, 54, 55)
1*PCI_F
33 MHz
(8)
7*PCI
33 MHz
(9,11,12,14,
15,17,18)
4*AGP (3V66)
66 MHz
(21,22,25,26)
2*CPU_DIV2
50/66 MHz
(49,50)
4*CPU
100/133 MHz
(41,42,45,46)
/3
/4
STOP
STOP
CPU_STOP
/3
/4
/2
STOP
CDC925
133-MHz CLOCK SYNTHESIZER/DRIVER FOR PC MOTHERBOARDS
WITH 3-STATE OUTPUTS
SCAS633 – JUL Y 28, 1999
6
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
absolute maximum ratings over operating free-air temperature range (unless otherwise noted)
†
Supply voltage range, VDD –0.5 V to 4.6 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input voltage range, VI (see Note 1) –0.5 V to 4.6 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Voltage range applied to any output in the high-impedance state or power-off state,
V
O
(see Note 1) –0.5 V to VDD + 0.5 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Current into any output in the low state, IO 2 × I
OL
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input clamp current, I
IK
(V
I
< 0) –18 mA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output clamp current, I
OK
(V
O
< 0) –50 mA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating free-air temperature range, T
A
–0°C to 85°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Storage temperature range, T
stg
–65°C to 150°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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.
DISSIPATION RATING TABLE
T
≤ 25°C DERATING FACTOR
†
T
= 70°C T
= 85°C
PACKAGE
A
POWER RATNG ABOVE TA = 25°C
A
POWER RATING
A
POWER RATING
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
θJA
) and uses a board-mounted device
at 80.2°C/W.
recommended operating conditions (see Note 2)
MIN NOM
†
MAX UNIT
pp
3.3 V 3.135 3.465
Suppl
y v
oltage, V
DD
2.5 V 2.375 2.625
V
High-level input voltage, V
IH
2
VDD +
0.3 V
V
Low-level input voltage, V
IL
GND –
0.3 V
0.8 V
Input voltage, V
I
0 V
DD
V
CPUx, CPU_DIV2x –12
p
APICx –12
High-level output current, I
OH
48MHz, REFx –14
mA
PCIx, PCI_F, 3V66x –18
CPUx, CPU_DIV2x 12
p
APICx 12
Low-level output current, I
OL
48MHz, REFx 9
mA
PCIx, PCI_F, 3V66x 12
Reference frequency, f
(XIN)
‡
Test mode 130 MHz
Crystal frequency, f
(XTAL)
§
Normal mode 13.8 14.318 14.8 MHz
Operating free-air temperature, T
A
0 85 °C
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
(XIN)
= 130 MHz. If XIN is driven externally, XOUT is floating.
§
This is a series fundamental crystal with fO = 14.31818 MHz.
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