Where f
CK
is the frequency of the DPLL output clock, LDR is the loop divider ratio integer part, LDRFRAC
is the loop divider ratio fractional part,
f
CKR
is the frequency of the selected reference clock, and PRESC
is the output prescaler value.
Figure 21-2. DPLL Block Diagram
XIN
XOUT
XOSC
XIN32
XOUT32
XOSC32K
GCLK
DIVIDER
DPLLCTRLB.DIV
DPLLCTRLB.REFCLK
DIGITAL FILTER
TDC
DPLLCTRLB.FILTER
DCO
CKDIV4
CKDIV2
CKDIV1
DPLLPRESC
CLK_DPLL
RATIO
DPLLRATIO
CK
CKR
CG
When the controller is disabled, the output clock is low. If the Loop Divider Ratio Fractional part bit field in
the DPLL Ratio register (DPLLRATIO.LDRFRAC) is zero, the DPLL works in integer mode. Otherwise,
the fractional mode is activated. Note that the fractional part has a negative impact on the jitter of the
DPLL.
Example (integer mode only): assuming F
CKR
= 32kHz and F
CK
= 48MHz, the
multiplication ratio is 1500. It means that LDR shall be set to 1499.
Example (fractional mode): assuming F
CKR
= 32kHz and F
CK
= 48.006MHz, the
multiplication ratio is 1500.1875 (1500 + 3/16). Thus LDR is set to 1499 and LDRFRAC
to 3.
Related Links
GCLK - Generic Clock Controller
on page 121
OSC32KCTRL – 32KHz Oscillators Controller
on page 258
21.6.6.1. Basic Operation
Initialization, Enabling, Disabling, and Resetting
The DPLLC is enabled by writing a '1' to the Enable bit in the DPLL Control A register
(DPLLCTRLA.ENABLE). The DPLLC is disabled by writing a zero to this bit.
The DPLLSYNCBUSY.ENABLE is set when the DPLLCTRLA.ENABLE bit is modified. It is cleared when
the DPLL output clock CK has sampled the bit at the high level after enabling the DPLL. When disabling
the DPLL, DPLLSYNCBUSY.ENABLE is cleared when the output clock is no longer running.
Figure 21-3. Enable Synchronization Busy Operation
ENABLE
CK
SYNCBUSY.ENABLE
CLK_APB_OSCCTRL
The frequency of the DPLL output clock CK is stable when the module is enabled and when the Lock bit
in the DPLL Status register is set (DPLLSTATUS.LOCK).
When the Lock Time bit field in the DPLL Control B register (DPLLCTRLB.LTIME) is non-zero, a user
defined lock time is used to validate the lock operation. In this case the lock time is constant. If
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
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