ACS8522 데이터 시트보기 (PDF) - Semtech Corporation

부품명

상세내역

제조사

ACS8522

Synchronous Equipment Timing Source for Stratum 3/4E/4 and SMC Systems

Semtech Corporation 

ADVANCED COMMUNICATIONS

FINAL

Figure 3 Inactivity and Irregularity Monitoring

Inactivities/Irregularities

ACS8522 SETS LITE

DATASHEET

Reference

Source

Leaky

Bucket

Response

Alarm

Programmable Fall Slopes

bucket_size

upper_threshold

lower_threshold

(all programmable)

Leaky Bucket Timing

The time taken (in seconds) to raise an inactivity alarm on

a reference source that has previously been fully active

(Leaky Bucket empty) will be:

(cnfg_upper_threshold_n) / 8

where n is the number of the Leaky Bucket Configuration.

If an input is intermittently inactive then this time can be

longer. The default setting of cnfg_upper_threshold is 6,

therefore the default time is 0.75 s.

The time taken (in seconds) to cancel the activity alarm on

a previously completely inactive reference source is

calculated, for a particular Leaky Bucket, as:

[2 (a) x (b - c)]/ 8

where:

a = cnfg_decay_rate_n

b = cnfg_bucket_size_n

c = cnfg_lower_threshold_n

(where n = the number of the relevant Leaky Bucket

Configuration in each case).

The default setting is shown in the following:

[21 x (8 - 4)] /8 = 1.0 secs

Frequency Monitoring

The ACS8522 performs input frequency monitoring to

identify reference sources which have drifted outside the

acceptable frequency range measured with respect either

to the output clock or to the XO clock.

The sts_reference_sources out-of-band alarm for a

particular reference source is raised when the reference

source is outside the acceptable frequency range. With

the default register settings a soft alarm is raised if the

drift is outside ±11.43 ppm and a hard alarm is raised if

the drift is outside ±15.24 ppm. Both of these limits are

programmable from 3.8 ppm up to 61 ppm.

The ACS8522 DPLL has a programmable lock and

capture range frequency limit up to ±80 ppm (default is

±9.2 ppm).

Selection of Input Reference Clock Source

Under normal operation, the input reference sources are

selected automatically by an order of priority. But, for

special circumstances, such as chip or board testing, the

selection may be forced by configuration.

Automatic operation selects a reference source based on

its pre-defined priority and its current availability. A table

is maintained which lists all reference sources in the order

of priority. This is initially defined by the default

configuration and can be changed via the Serial interface

by the Network Manager. In this way, when all the defined

sources are active and valid, the source with the highest

programmed priority is selected but, if this source fails,

the next-highest source is selected, and so on.

Restoration of repaired reference sources is handled

carefully to avoid inadvertent disturbance of the output

clock. For this, the ACS8522 has two modes of operation;

Revertive and Non-revertive.

Revision 5/November 2006 © Semtech Corp.

Page 12

www.semtech.com

Share Link: