ics409 Integrated Device Technology, ics409 Datasheet - Page 2

• Manufacturer Part Number: ics409
• Description: Pc Peripheral Clock
• Manufacturer: Integrated Device Technology

IDT™ / ICS™ PC PERIPHERAL CLOCK
ICS409
PC PERIPHERAL CLOCK
Pin Assignment
Pin Descriptions
External Components
Series Termination Resistor
Clock output traces over one inch should use series
termination. To series terminate a 50Ω trace (a
commonly used trace impedance), place a 33Ω resistor
in series with the clock line, as close to the clock output
pin as possible. The nominal impedance of the clock
output is 20Ω .
Decoupling Capacitor
As with any high performance mixed-signal IC, the
ICS409 must be isolated from system power supply
noise to perform optimally.
A decoupling capacitor of 0.01µF must be connected
between VDD and the PCB ground plane.
O E / L A T
V D D
1
2
3
4
5
6
7
8
Number
X 1
X 2
8 P i n ( 1 5 0 m i l ) S O I C
Pin
1
2
3
4
OE/LAT
X1
X2
VDD
40/80M
GND
25M
25M
Name
Pin
8
7
6
5
Output
Output
Output
Power
Power
Type
Input/
Input
Input
Input
Pin
2 5 M
G N D
2 5 M
4 0 / 8 0 M
Disables or latches 40/80 MHz output dependant on pin 5 level.
Crystal connection. Connect to 14.31818 MHz parallel mode crystal.
Crystal connection. Connect to 14.31818 MHz parallel mode crystal.
Connect to voltage supply.
Tri-state when OE/LAT is low.
Connect to ground.
25 MHz clock output.
25 MHz clock output.
40M or 80M selection pin and clock output (see below for operation).
2
40/80M Frequency Selection
Note: See below for operations of frequency selection
Crystal Load Capacitors
The device crystal connections should include pads for
small capacitors from X1 to ground and from X2 to
ground. These capacitors are used to adjust the stray
capacitance of the board to match the nominally
required crystal load capacitance. Because load
capacitance can only be increased in this trimming
process, it is important to keep stray capacitance to a
minimum by using very short PCB traces (and no vias)
between the crystal and device. Crystal capacitors must
be connected from each of the pins X1 and X1 to
ground.
The value (in pF) of these crystal caps should equal (C
-6pF)*2. In this equation, C
40/80M (pin 5)
Pin Description
0
1
L
= crystal load capacitance
Output Freq
40M
80M
ICS409
CLOCK SYNTHESIZER
REV D 092109
L