PL135-37

Low Power, 1.62V to 3. 63V, 10M Hz to 40M Hz, 1:3 O scillat or Fanout Buffer

Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1(408) 944 -0800 • fax +1(408) 474-1000 • www.micrel.com Rev 03/18/11 Page 2

PIN DESCRIPTION

Name

SOP-8L

Type

Description

XIN

1

I

Crystal input

OE

2

I

Output enable input. This pin has internal pull-up resistor. All outputs will be

tri-stated when pulled low.

CLK1

3

O

Output clock

GND

4

P

Ground connection

CLK2

5

O

Output clock

VDD

6

P

Power supply

CLK0

7

O

Output clock

XOUT

8

I

Crystal output

* Note: This pin includes an internal 60KΩ pull up.

LAYOUT RECOMMENDATIONS

The following guidelines are to assist you with a performance optimized PCB design:

Signal Integrity and Termination Considerations

- Keep traces short!

- Trace = Inductor. With a capacitive load this equals

ringing!

- Long trace = Transmission Line. Without proper ter-

mination this will cause reflections (looks like ringing).

- Design long traces as “striplines” or “microstrips” with

defined impedance.

- Match trace at one side to avoid reflections bouncing

back and forth.

Decoupling and Power Supply Considerations

- Place decoupling capacitors as close as possible to

the VDD pin(s) to limit noise from the power supply

- Multiple VDD pins should be decoupled separately

for best performance.

- Addition of a ferrite bead in series with V DD can

help prevent noise from other board sources

- Value of decoupling capacitor is frequency de-

pendant. Typical value to use is 0.1

F.

Typical CMOS termination

Place Series Resistor as close as possible to CMOS output

CMOS Output Buffer

(Typical buffer impedance 20Ω)

To CMOS Input

Series Resistor

Use value to match output buffer impedance to

50Ω trace. Typical value 30Ω

50Ω line

Crystal Tuning Circuit

Series and parallel capacitors used to fine tune the crystal load to the circuit load.

CST – Series Capacitor, used to lower circuit load to match crystal load. Raises frequency offset.

This can be eliminated by using a crystal with a Cload of equal or greater value than the oscillator.

CPT – Parallel Capacitors, Used to raise the circuit load to match the crystal load. Lowers

frequency offset.

Crystal

XIN

1

8

XOUT

Cpt

Cpt

Cst