48 MHz Tiny USB Clock Source

MDS 5OSK481 B

2

Revision 111805

Integrated Circuit Systems, Inc.

PRELIM INAR Y INFORM A T ION

ICS5OSK481

Pin Assignment

Pin Descriptions

External Components

Decoupling Capacitor

As with any high-performance mixed-signal IC, the

ICS5OSK481 must be isolated from system power

supply noise to perform optimally.

A decoupling capacitor of 0.01µF must be connected

between each VDD and the PCB ground plane.

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.

PCB Layout Recommendations

For optimum device performance and lowest output

phase noise, the following guidelines should be

observed.

1) The 0.01µF decoupling capacitors should be

mounted on the component side of the board as close

to the VDD pin as possible. No vias should be used

between the decoupling capacitors and VDD pins. The

PCB trace to VDD pins should be kept as short as

possible, as should the PCB trace to the ground via.

2) To minimize EMI, the 33

Ω series termination resistor

(if needed) should be placed close to the clock output.

3) An optimum layout is one with all components on the

same side of the board, minimizing vias through other

signal layers. Other signal traces should be routed

away from the ICS5OSK481. This includes signal

traces just underneath the device, or on layers adjacent

to the ground plane layer used by the device.

OE

GN D

CLK

ICLK

1

2

3

5

4

VDD

Pin

Number

Pin

Name

Pin

Type

Pin Description

1

ICLK

Input

25 MHz clock input. Connect to a parallel resonant fundamental crystal or

input clock.

2

GND

Power

Connect to ground.

3

CLK

Output

PLL output clock. Internal pull-down resistor.

4

VDD

Power

Connect to 3.3 V.

5

OE

Input

Output Enable pin. Internal pull-up resistor. OE=0 outputs tristate with weak

pull-down.