November 2006

ASM5P23S04A

rev 1.4

3.3 ‘SpreadTrak’ Zero Delay Buffer

2 of 15

Notice: The information in this document is subject to change without notice.

ASM5P23S04A Configurations

Device

Feedback From

Bank A Frequency

Bank B Frequency

ASM5P23S04A-1

Bank A or Bank B

Reference

Reference

ASM5P23S04A-1H

Bank A or Bank B

Reference

Reference

ASM5P23S04A-2

Bank A or Bank B

Reference

Reference /2

ASM5P23S04A-2H

Bank A or Bank B

Reference

Reference /2

‘SpreadTrak’

Many systems being designed now utilize a technology

called Spread Spectrum Frequency Timing Generation.

ASM5P23S04A is designed so as not to filter off the

Spread Spectrum feature of the Reference Input, assuming

it exists. When a zero delay buffer is not designed to pass

the Spread Spectrum feature through, the result is a

significant amount of tracking skew which may cause

problems in the systems requiring synchronization.

Zero Delay and Skew Control

For applications requiring zero input-output delay, all

outputs must be equally loaded.

To close the feedback loop of the ASM5P23S04A, the FBK

pin can be driven from any of the four available output pins.

The output driving the FBK pin will be driving a total load of

7pF plus any additional load that it drives. The relative

loading of this output (with respect to the remaining

outputs) can adjust the input output delay. This is shown in

the above graph.

For applications requiring zero input-output delay, all

outputs including the one providing feedback should be

equally loaded. If input-output delay adjustments are

required, use the above graph to calculate loading

differences between the feedback output and remaining

outputs. For zero output-output skew, be sure to load

outputs equally.

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

0

-500

-1000

-1500

500

1000

1500

Output Load Difference: FBK Load - CLKA/CLKB Load (pF)

REF Input to CLKA/CLKB Delay Vs Difference in Loading between FBK pin and CLKA/CLKB pins