1.4 DSPLL Loop Bandwidth
The DSPLL loop bandwidth determines the amount of input clock jitter attenuation and wander filtering. Register configurable DSPLL
loop bandwidth settings in the range of 20 Hz to 4 kHz are available for selection. The DSPLL loop bandwidth register values are
determined using ClockBuilder Pro.
CBPro chooses the PLL parameters so that peaking in passband of the PLL is less than 0.1 dB.
Note:
After manually changing bandwidth parameters, the BW_UPDATE bit must be set high to latch the new values into operation.
This update bit will latch the new values for Loop, Fastlock, and Holdover Exit bandwidths simultaneously.
Table 1.2. DSPLL Loop Bandwidth Registers
Register Name
Hex Address
[Bit Field]
Function
BW_PLL
0x0508[7:0]-0x050D[7:0]
Determines the loop BW for the DSPLL.
Parameters are generated by ClockBuilder
Pro.
BW_UPDATE
0x0514[0]
Writing a 1 to this register bit will latch
Loop, Fastlock, and Holdover Exit BW pa-
rameter registers.
1.4.1 Fastlock
Selecting a low DSPLL loop bandwidth (e.g., 20 Hz) will generally lengthen the lock acquisition time. The Fastlock feature allows
setting a temporary Fastlock Loop Bandwidth that is used during the lock acquisition process to reduce lock time. Higher Fastlock loop
bandwidth settings will enable the DSPLLs to lock faster. Fastlock Bandwidth settings up to 4 kHz are available for selection. Fastlock
bandwidth should generally be set from 10x to 100x the loop bandwidth for optimal results. Once lock acquisition has completed,
the DSPLL’s loop bandwidth will automatically revert to the DSPLL Loop Bandwidth setting. The Fastlock feature can be enabled or
disabled independently by register control.
Note:
The BW_UPDATE_PLLx update bit will latch new values for Loop, Fastlock, and Holdover Exit bandwidths simultaneously.
Table 1.3. DSPLL Fastlock Bandwidth Registers
Register Name
Hex Address
[Bit Field]
Function
FASTLOCK_BW_PLL
0x050E[5:0]-0x0513[5:0]
Determines the Fastlock BW for the DSPLL. Parameters
are generated by ClockBuilder Pro.
FASTLOCK_AUTO_EN
0x052B[0]
Auto Fastlock Enable/Disable.
0: Disable Auto Fastlock (default)
1: Enable Auto Fastlock
FASTLOCK_MAN
0x052B[1]
Force Fastlock.
0: Normal Operation (default)
1: Force Fastlock
.
Si5386 Rev. E Reference Manual • Functional Description
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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