Setting Name
Hex Address [Bit Field]
Function
Si5397
Si5396
LOS(3,2,1,0)_FLG
0012[3:0]
0012[3:0]
LOS status monitor sticky bits for IN3, IN2, IN1, IN0.
Sticky bits will remain asserted when an LOS event oc-
curs until they are cleared. Writing a zero to a sticky bit
will clear it.
LOSXAXB_FLG
0011[1]
0011[1]
LOS status monitor sticky bits for XAXB. Sticky bits will
remain asserted when an LOS event occurs until
cleared. Writing a zero to a sticky bit will clear it.
LOS Fault Monitor Controls and Settings
LOS(3,2,1,0)_EN
002C[3:0]
002C[3:0]
LOS monitor enable for IN3, IN2, IN1, IN0. Allows disa-
bling the monitor if unused.
LOS(3,2,1,0)_TRG_THR
002E[7:0] -
0035[7:0]
002E[7:0] -
0035[7:0]
Sets the LOS trigger threshold and clear sensitivity for
IN3, IN2, IN1, IN0. These 16-bit values are determined
with the ClockBuilder Pro utility. The trigger threshold
sets the maximum period and the clear threshold sets
the minimum period.
LOS(3,2,1,0)_CLR_THR
0036[7:0] -
003D[7:0]
0036[7:0] -
003D[7:0]
5.3.2 Out of Frequency (OOF) Fault 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
directly below. An option to disable either monitor is also available. The live OOF register always displays the current OOF state and its
sticky register bit stays asserted until cleared.
en
en
Precision
Fast
OOF
Monitor
LOS
OOF
Sticky
Live
Figure 5.9. 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 of 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 XAXB pins is available. These options are all register configurable.
Si5397/96 Reference Manual
Clock Inputs
silabs.com
| Building a more connected world.
Rev. 0.9 | 31