3.3.3 Loss of Lock (LOL) Fault Monitoring
The Loss of Lock (LOL) monitor asserts a LOL register bit when the DSPLL has lost synchronization with its selected input clock.
There is also a dedicated loss of lock pin that reflects the loss of lock condition. The LOL monitor functions by measuring the frequency
difference between the input and feedback clocks at the phase detector. There are four parameters that control the LOL monitor. First,
there is an
assert threshold
which sets the LOL assertion threshold. The user sets this threshold in ppm in CBPro. Then, there is a
fast assert threshold
. CBPro sets this to ~100 times the assert threshold. Then there is a
de-assert threshold
to clear the LOL, which
is set in ppm in CBPro. Then, there is a
clear delay
, which CBPro sets based upon the project plan.
Note:
A very large ppm error in a short time will assert LOL.
A block diagram of the LOL monitor is shown below. The live LOL register always displays the current LOL state and a sticky register
always stays asserted until cleared. The LOL pin reflects the current state of the LOL monitor.
DSPLL
LPF
PD
÷M
LOL
Clear
LOL
Set
Timer
LOLb
LOS
LOL
Sticky
Live
LOL Monitor
f
IN
Feedback
Clock
÷5
Figure 3.9. Si5386 LOL Status Indicator
The LOL frequency monitors have an adjustable sensitivity which is register configurable from 0.1 ppm to 10000 ppm. CBPro provides
a wide range of set and clear thresholds for the LOL function. Having two separate frequency monitors allows for hysteresis to help
prevent chattering of LOL status. An example configuration of the LOL set and clear thresholds is shown below.
Phase Detector Frequency Difference (ppm)
Hysteresis
LOL
LOCKED
Clear LOL
Threshold
Set LOL
Threshold
Lock Acquisition
0
Lost Lock
0.1
1
10,000
Figure 3.10. LOL Set and Clear Thresholds
Si5386 Rev. E Reference Manual • Clock Inputs
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
30
Rev. 1.2 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • December 9, 2021
30