MDS 409 C

2

Revision 111005

www.icst.com

ICS409

Pin Assignment

40/80M Frequency Selection

Note: See below for operations of frequency selection

Pin Descriptions

External Components

Series Termination Resistor

Clock output traces over one inch should use series

termination. To series terminate a 50

Ω trace (a

commonly used trace impedance), place a 33

Ω resistor

in series with the clock line, as close to the clock output

pin as possible. The nominal impedance of the clock

output is 20

Ω.

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.

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)

been 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

capacitance in pF. Example: For a crystal with a 15 pF

1

2

3

OE / L A T

4

GN D

40/ 80M

25M

25 M

X2

VD D

8

7

6

5

X1

8 P i n (150 m il) S O IC

40/80M (pin 5)

Output Freq

0

40M

1

80M

Pin

Number

Pin

Name

Pin

Type

Pin Description

1

OE/LAT

Input

Disables or latches 40/80 MHz output dependant on pin 5 level.

2

X1

Input

Crystal connection. Connect to 14.31818 MHz parallel mode crystal.

3

X2

Input

Crystal connection. Connect to 14.31818 MHz parallel mode crystal.

4

VDD

Power

Connect to voltage supply.

5

40/80M

Input/

Output

40M or 80M selection pin and clock output (see below for operation).

Tri-state when OE/LAT is low.

6

GND

Power

Connect to ground.

7

25M

Output

25 MHz clock output.

8

25M

Output

25 MHz clock output.