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MK1491-09
AMD Geode™ GX2 Clock Source
Description
The MK1491-09 is a low-cost, low-jitter,
high-performance clock synthesizer for AMD’s
Geode-based computer and portable appliance
applications. Using patented analog Phased-Locked
Loop (PLL) techniques, the device accepts a 14.318
MHz crystal input to produce multiple output clocks. It
provides selectable PCI local bus clocks, 48 MHz
clocks for Super I/O and USB, as well as multiple
Reference outputs.
The device has multiple power-down modes to reduce
power consumption.
Block Diagram
VDD
6
GND
6
Features
Packaged in 28-pin SSOP (209 mil body)
Available in Pb (lead) free packaged
Provides all critical timing for the AMD Geode
companion chip
Four selectable PCI clocks
Three LPC interface clocks
One Fixed 66 MHz clock
2 Reference clocks
48 MHz USB and 48 MHz IO support
Power down mode
Low EMI Enable pin reduces EMI radiation on PCI
clocks, LCLKS, and 66 MHz clock
Operating voltage of 3.3 V ±5%
Sel66/33#
PD#
Clocks
4 PCI (66/33 MHz)
3 LCLK (33 MHz)
66 MHz
14.31818 MHz
crystal
XI
XO
Crystal
Oscillator
USB
Clock
48/TS#
48 MHz
REFCLK1
REFCLK0/Spread#
MDS 1491-09 G
1
Revision 080204
Integrated Circuit Systems, Inc. 525 Race Street, San Jose, CA 95126 tel (408) 297-1201 www.icst.com

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MK1491-09
AMD Geode™ GX2 Clock Source
Pin Assignment
GND
XI
XO
VDD
LCLK0/33M
LCLK1/33M
GND
VDD
LCLK2/33M
Sel66/33#
GND
VDD
48M
48M/TS#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28 VDD
27 RefCLK0/Spread#
26 RefCLK1
25 VDD
24 PCICLK3/33-66M
23 PCICLK2/33-66M
22 GND
21 GND
20 PCICLK1/33-66M
19 VDD
18 PCICLK0/33-66M
17 PD#
16 66M
15 GND
PCI Frequency Select Table
Sel66/33#
0
1
PCI Frequency
33 MHz
66 MHz
EMI Control
Spread#
0
1
PCI Low EMI
ON
OFF
Spread direction is DOWN.
Pin Descriptions
Pin
Number
1, 7, 11, 15, 21, 22
2
3
4, 8, 12, 19, 25, 28
5, 6, 9
10
13
14
16
17
18, 20, 23, 24
26
27
Pin
Name
GND
XI
XO
VDD
LCLK
Sel66/33#
48M
48M/TS#
66M
PD#
PCICLK
RefCLK1
RefCLK0/
Spread#
Pin
Type
Pin Description
P Connect to Ground.
I Crystal connection. Connect to a 14.31818 MHz crystal or input clock.
O Crystal connection. Connect to a 14.31818 MHz crystal, or leave
unconnected.
P Connect to 3.3 V.
O 33 MHz low skew clock outputs.
I Selects frequency on PCICLK.
O 48 MHz clock output.
I/O 48 MHz clock output. TS# is high at power-up.
O 66 MHz clock output.
I Power-down input (see table on page 3).
O 33 to 66 MHz PCI synchronous clock outputs with low skew.
O Buffered reference output of 14.31818 MHz.
I/O Buffered reference output of 14.31818 MHz. Spread select at
power-up. For Spread#, see table above.
KEY: I = Input, TI = Tri-level, O = Output, P = Power supply connection, (T)I/O = Input on power up,
becomes an Output after 10 ms, Weak internal pull-up resistors are present on TS#, Spread#, PD#, and
Sel66/33.
MDS 1491-09 G
2
Revision 080204
Integrated Circuit Systems, Inc. 525 Race Street, San Jose, CA 95126 tel (408) 297-1201 www.icst.com

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MK1491-09
AMD Geode™ GX2 Clock Source
Power Down Control Table
PD#
0
1
Functions
All clocks are stopped low.
All clocks are running.
Power-on Default Conditions
Pin #
14
27
17
10
Function
TS#
Spread#
PD#
Sel66/33
Default
Condition
H All outputs enabled.
H Spread disabled.
H PCI clocks set to 33.3 MHz. Refer to Power Down Control Table above.
H PCI frequency = 66 MHz.
MDS 1491-09 G
3
Revision 080204
Integrated Circuit Systems, Inc. 525 Race Street, San Jose, CA 95126 tel (408) 297-1201 www.icst.com

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MK1491-09
AMD Geode™ GX2 Clock Source
External Components
The MK1491-09 requires some inexpensive external
components for proper operation. Decoupling
capacitors of 0.1µF should be connected on each VDD
pin to ground, as close to the MK1491-09 as possible.
A series termination resistor of 33may be used for
each clock output. See the discussion below for other
external resistors required for proper I/O operation. The
14.318 MHz oscillator has internal caps that provide
the proper load for a parallel resonant crystal with
CL=18 pF. For tuning with other values of CL, the
formula 2*(CL-18) gives the value of each capacitor that
should be connected between X1 and ground and X2
and ground.
I/O Structure
The MK1491-09 provides more functionality in a 28-pin
package by using a unique I/O technique. The device
checks the status of all I/O pins during power-up. This
status (pulled high or low) then determines the
frequency selections and power down modes (see the
tables on pages 2 and 3). Within 10ms after power up,
the inputs change to outputs and the clocks start up. In
the diagrams below, the 33resistors are the normal
output termination resistors. The 10kresistor pulls
low to generate a logic zero when needed. Weak
internal pull-up resistors are present on TS#, Spread#,
PD#, and Sel66/33 to pull the pin to high when left
floating.
For select
= 0 (low)
I/O
10 k
33
To load*
Do not stuff for
“1” selection
*Note: Do not use a TTL load. This will overcome the
10 kpull-down and force the input to a logic 1.
MDS 1491-09 G
4
Revision 080204
Integrated Circuit Systems, Inc. 525 Race Street, San Jose, CA 95126 tel (408) 297-1201 www.icst.com

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MK1491-09
AMD Geode™ GX2 Clock Source
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the MK1491-09. These ratings,
which are standard values for ICS commercially rated parts, are stress ratings only. Functional operation of
the device at these or any other conditions above those indicated in the operational sections of the
specifications is not implied. Exposure to absolute maximum rating conditions for extended periods can
affect product reliability. Electrical parameters are guaranteed only over the recommended operating
temperature range.
Item
Supply Voltage, VDD (referenced to VSS)
All Inputs and Outputs (referenced to VSS)
Ambient Operating Temperature
Storage Temperature
Junction Temperature
Soldering Temperature (10 seconds max)
Spread Spectrum Enabled for PCI and LPC Clocks
Rating
4.6 V
-0.5 V to VDD+0.5 V
0 to +70°C
-65 to +150°C
125°C
260°C
30 kHz min., 33 kHz max.
DC Electrical Characteristics
Unless stated otherwise, VDD = 3.3 V, Ambient Temperature 0 to +70°C
Parameter
Symbol
Conditions
Min.
Operating Voltage
VDD
3.13
Input High Voltage
Input Low Voltage
Output High Voltage
Output Low Voltage
Operating Supply Current
VIH
VIL
VOH
VOL
IDD
IOH = -12 mA
IOL = 12 mA
VDD = 3.3 V
2
VSS
2.4
Clock Disable Mode
Supply Current
Internal Pull-up Resistor
All inputs except XI
Input Capacitance
CIN All inputs except XI
Typ.
3.3
5
Max.
3.46
VDD
0.8
0.4
60
0.5
Units
V
V
V
V
V
mA
mA
k
pF
MDS 1491-09 G
5
Revision 080204
Integrated Circuit Systems, Inc. 525 Race Street, San Jose, CA 95126 tel (408) 297-1201 www.icst.com