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Si53xx-RM
Rev. 0.52
83
7.4.2.2. Detailed Automatic Clock Selection Description (Si5367, Si5368, Si5369)
The prioritization of clock inputs for automatic switching is shown in Table 41. For example, if
CK_CONFIG_REG
= 0 and the desired clock priority order is CKIN4, CKIN3, CKIN2, and then CKIN1 as the
lowest priority clock, the user should set
CK_PRIOR1
[1:0] = 11,
CK_PRIOR2
[1:0] = 10,
CK_PRIOR3
[1:0] = 01, and
CK_PRIOR4
[1:0] = 00.
If
CK_CONFIG_REG
= 1 and the desired clock priority is CKIN1/CKIN3 and then CKIN2/CKIN4, the user should
set
CK_PRIOR1
[1:0] = 00 and
CK_PRIOR2
[1:0] = 01 (
CK_PRIOR3
[1:0] and
CK_PRIOR4
[1:0] are ignored in this
case).
The following discussion describes the clock selection algorithm for the case of four possible input clocks
(
CK_CONFIG_REG
= 0) in the default priority arrangement (priority order CKIN1, CKIN2, CKIN3, CKIN4).
Automatic switching mode selects CKIN1 at powerup, reset, or when in revertive mode with no alarms present on
CKIN1. If an alarm condition occurs on CKIN1 and there are no active alarms on CKIN2, the device switches to
CKIN2. If both CKIN1 and CKIN2 are alarmed and there is no alarm on CKIN3, the device switches to CKIN3. If
CKIN1, CKIN2, and CKIN3 are alarmed and there is no alarm on CKIN4, the device switches to CKIN4. If alarms
exist on CKIN1, CKIN2, CKIN3, and CKIN4, the device enters digital hold mode. If automatic mode is selected and
the frequency offset alarms (
FOS1_INT
,
FOS2_INT
,
FOS3_INT
,
FOS4_INT
) are disabled, automatic switching is
not initiated in response to FOS alarms. The loss-of-signal alarms (
LOS1_INT
,
LOS2_INT
,
LOS3_INT
,
LOS4_INT
)
are always used in making automatic clock selection choices. In non-revertive mode, once CKIN2 is selected,
CKIN2 selection remains as long as it is valid even if alarms are cleared on CKIN1.
7.4.3. Hitless Switching with Phase Build-Out (Si5324, Si5326, Si5327, Si5368, Si5369, Si5374)
Silicon Laboratories switching technology performs phase build-out, which maintains the phase of the output when
the input clock is switched. This minimizes the propagation of phase transients to the clock outputs during input
clock switching. All switching between input clocks occurs within the input multiplexer and phase detector circuitry.
The phase detector circuitry continually monitors the phase difference between each input clock and the DSPLL
output clock, f
OSC
. The phase detector circuitry can lock to a clock signal at a specified phase offset relative to f
OSC
so that the phase offset is maintained by the PLL circuitry.
At the time a clock switch occurs, the phase detector circuitry knows both the input-to-output phase relationship for
the original input clock and for the new input clock. The phase detector circuitry locks to the new input clock at the
new clock's phase offset so that the phase of the output clock is not disturbed. The phase difference between the
two input clocks is absorbed in the phase detector's offset value, rather than being propagated to the clock output.
The switching technology virtually eliminates the output clock phase transients traditionally associated with clock
rearrangement (input clock switching).
Note that hitless switching between input clocks applies only when the input clock validation time is
VALTIME
[1:0] = 01 or higher.
Table 41. Input Clock Priority for Auto Switching
Selected Clock
CK_PRIORn[1:0]
CK_CONFIG_REG = 0
CK_CONFIG_REG = 1
00
CKIN1
CKIN1/CKIN3
01
CKIN2
CKIN2/CKIN4
10
CKIN3
Not Used
11
CKIN4
Not Used
Summary of Contents for Si5316 Series
Page 2: ...Si53xx RM 2 Rev 0 52 ...
Page 110: ...Si53xx RM 110 Rev 0 52 Figure 48 sfout_5 LVPECL Figure 49 sfout_6 CML ...
Page 111: ...Si53xx RM Rev 0 52 111 Figure 50 sfout_7 LVDS ...
Page 127: ...Si53xx RM Rev 0 52 127 Figure 66 155 52 MHz In 622 08 MHz Out Loop BW 7 Hz Si5324 ...
Page 128: ...Si53xx RM 128 Rev 0 52 Figure 67 19 44 MHz In 156 25 MHz Out Loop BW 80 Hz ...
Page 129: ...Si53xx RM Rev 0 52 129 Figure 68 19 44 MHz In 156 25 MHz Out Loop BW 5 Hz Si5324 ...
Page 131: ...Si53xx RM Rev 0 52 131 Figure 70 61 44 MHz In 491 52 MHz Out Loop BW 7 Hz Si5324 ...
Page 132: ...Si53xx RM 132 Rev 0 52 Figure 71 622 08 MHz In 672 16 MHz Out Loop BW 6 9 kHz ...
Page 133: ...Si53xx RM Rev 0 52 133 Figure 72 622 08 MHz In 672 16 MHz Out Loop BW 100 Hz ...
Page 134: ...Si53xx RM 134 Rev 0 52 Figure 73 156 25 MHz In 155 52 MHz Out ...
Page 139: ...Si53xx RM Rev 0 52 139 Figure 78 86 685 MHz In 173 371 MHz Out ...
Page 140: ...Si53xx RM 140 Rev 0 52 Figure 79 86 685 MHz In 693 493 MHz Out ...
Page 142: ...Si53xx RM 142 Rev 0 52 Figure 81 10 MHz In 1 GHz Out ...
Page 174: ...Si53xx RM 174 Rev 0 52 Figure 99 Si5374 Si5375 DSPLL A ...
Page 175: ...Si53xx RM Rev 0 52 175 Figure 100 Si5374 Si5375 DSPLL B ...
Page 176: ...Si53xx RM 176 Rev 0 52 Figure 101 Si5374 Si5375 DSPLL C ...