3.3.2 Out-of-Frequency (OOF) Detection
Each input clock is monitored for frequency accuracy with respect to an OOF reference which it considers as its 0 ppm reference. This
OOF reference can be selected as either:
• XA/XB pins
• Any input clock (IN0, IN1, IN2, IN3)
The final OOF status is determined by the combination of both a precise OOF monitor and a fast OOF monitor as shown in the figure
below. An option to disable either monitor is also available. The live OOF register always displays the current OOF state and its sticky
flag register bit stays asserted until cleared.
en
en
Precision
Fast
OOF
Monitor
LOS
OOF
Sticky
Live
Figure 3.7. OOF Status Indicator
The Precision OOF monitor circuit measures the frequency of all input clocks to within up to ±0.0625 ppm accuracy with respect to the
selected OOF frequency reference. A valid input clock frequency is one that remains within the register-programmable OOF frequency
range from ±0.0625 ppm to ±512 ppm in steps of 1/16 ppm. A configurable amount of hysteresis is also available to prevent the OOF
status from toggling at the failure boundary. An example is shown in the figure below. In this case, the OOF monitor is configured with
a valid frequency range of ±6 ppm and with 2 ppm of hysteresis. An option to use one of the input pins (IN0–IN3) as the 0 ppm OOF
reference instead of the XA/XB pins is available. These options are all register configurable.
OOF
Reference
Hysteresis
Hysteresis
OOF Declared
OOF Cleared
-6 ppm
-4 ppm
0 ppm
+4 ppm
+6 ppm
f
IN
(Clear)
(Set)
(Clear)
(Set)
Figure 3.8. Example of Precision OOF Monitor Assertion and De-assertion Triggers
The table below lists the OOF monitoring and control registers. Because the precision OOF monitor needs to provide 1/16 ppm
of frequency measurement accuracy, it must measure the monitored input clock frequencies over a relatively long period of time.
However, this may be too slow to detect an input clock that is quickly ramping in frequency. An additional level of OOF monitoring called
the Fast OOF monitor runs in parallel with the precision OOF monitors to quickly detect a ramping input frequency. The Fast OOF
responds more quickly and has larger thresholds.
Table 3.9. Out-of-Frequency Status Monitoring and Control Registers
Register Name
Hex Address
[Bit Field]
Function
OOF
0x000D[7:4]
OOF status monitor for IN3, IN2, IN1, IN0. Indicates if a valid
clock is detected or if a OOF condition is detected.
OOF_FLG
0x0012[7:4]
OOF status monitor sticky bits for IN3, IN2, IN1, IN0. Stick bits will
remain asserted when an OOF event occurs until cleared. Writing
zero to the bit will clear it.
OOF_INTR_MSK
0x0018[7:4]
Masks OOF from generating INTR interrupt for IN3 – IN0.
0: Allow OOF interrupt (default)
1: Mask (ignore) OOF for interrupt
Si5386 Rev. E Reference Manual • Clock Inputs
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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Rev. 1.2 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • December 9, 2021
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