MK1491-14
OPTi ACPI Firestar Clock Source
33W
I/O Structure
to load
I/O
The MK1491 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 page 2). Within 10ms
after power up, the inputs change to outputs and the clocks start up. In the
diagrams to the right, the 33W resistors are the normal output
termination resistors. The 10kW resistor pulls low to generate a logic
zero. Internal pull-up resistors are present on all inputs to generate a logic
one when an external pull-down resistor is not connected.
For select
= 0 (low)
10kW
33W
For select
= 1 (high)
to load
I/O
Package Outline and Package Dimensions
28 pin SSOP
Inches
Millimeters
Symbol Min
Max
Min
Max
1.73
A
b
0.061 0.068 1.55
E
H
0.008 0.012 0.203 0.305
0.007 0.010 0.190 0.254
0.385 0.400 9.780 10.160
0.150 0.160 3.810 4.064
0.230 0.245 5.840 6.223
c
D
E
H
e
h x 45°
D
.025 BSC
0.016
0.004 0.01 0.127 0.254
0.635 BSC
h
0.410
A
c
Q
Q
b
e
Ordering Information
Part/Order Number
MK1491E-14R
Marking
Low EMI Feature
Package
Temperature
MK1491E-14R
MK1491E-14R
Yes
Yes
28 pin SSOP
0-70°C
-
MK1491E-14RTR
Add Tape & Reel
External Components
The MK1491 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 as possible. A series termination resistor of 33W may be used for each clock output. See the
discussion on page 4 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 C =18pF. For tuning with other values of C , the formula 2•(C -18) gives the value of each
L
L
L
capacitor that should be connected between X1 and ground and X2 and ground.
While the information presented herein has been checked for both accuracy and reliability, MicroClock Incorporated assumes no responsibility for either its use or for the
infringement of any patents or other rights of third parties, which would result from its use. No other circuits, patents, or licenses are implied. This product is intended for use in
normal commercial applications. Any other applications such as those requiring extended temperature range, high reliability, or other extraordinary environmental requirements
are not recommended without additional processing by MicroClock. MicroClock reserves the right to change any circuitry or specifications without notice. MicroClock does not
authorize or warrant any MicroClock product for use in life support devices or critical medical instruments.
Pentium is a trademark of Intel Corporation
MDS 1491-14 B
4
Revision 061801
Integrated Circuit Systems, Inc. • 525 Race Street • San Jose •CA •95126 • (408)295-9800tel • www.icst.com
ICSI [ INTEGRATED CIRCUIT SOLUTION INC ]
