Silicon Laboratories SI5375 - Manual (Page 52)

S i 5 3 x x - R M
52 Rev. 1.2
5.2. PLL Self-Calibration
An internal self-calibration (ICAL) is performed before operation to optimize loop parameters and jitter
performance. While the self-calibration is being performed, the DSPLL is being internally controlled by the self-
calibration state machine, and the LOL alarm will be active for narrowband parts.
Any of the following events will trigger a self-calibration:
 Power-on-reset (POR)
 Release of the external reset pin RST (transition of RST from 0 to 1)
 Change in FRQSEL, FRQTBL, BWSEL, or RATE pins
 Internal DSPLL registers out-of-range, indicating the need to relock the DSPLL.
In any of the above cases, an internal self-calibration will be initiated if a valid input clock exists (no input alarm)
and is selected as the active clock at that time. For the Si5316, Si5323 and Si5366, the external crystal or
reference clock must also be present for the self-calibration to begin. If valid clocks are not present, the self-
calibration state machine will wait until they appear, at which time the calibration will start. All outputs are on during
the calibration process.
After a successful self-calibration has been performed with a valid input clock, no subsequent self-calibrations are
performed unless one of the above conditions are met. If the input clock is lost following self-calibration, the device
enters digital hold mode. When the input clock returns, the device relocks to the input clock without performing a
self-calibration. (Narrow band devices only).
5.2.1. Input Clock Stability during Internal Self-Calibration (Si5316, Si5322, Si5323, Si5365, Si5366)
An exit from reset must occur when the selected CKINn clock is stable in frequency with a frequency value that is
within the operating range that is reported by DSPLLsim. The other CKINs must also either be stable in frequency
or squelched during a reset.
5.2.2. Self-Calibration caused by Changes in Input Frequency (Si5316, Si5322, Si5323, Si5365, Si5366)
If the selected CKINn varies by 500 ppm or more in frequency since the last calibration, the device may initiate a
self-calibration.
5.2.3. Recommended Reset Guidelines (Si5316, Si5322, Si5323, Si5365, Si5366)
Follow the recommended RESET guidelines in Table 11 and Table 12 when reset should be applied to a device.