9.4.4.1 DCO Frequency Step Size
Equation 16 shows the formula to compute the DPLLy_FDEV register value required to meet the specified DCO frequency step size in ppb (part-per-billion) when DCO mode is enabled for the REF-DPLL (when DPLLy_DCO_SEL_REF_TCXOB = 1).
Equation 16. DPLLy_FDEV = ( Reqd_ppb / 10
9 ) × DEN
REF / ( f
INx / R
INx ) × f
VCOy / ( P1
PLLy × PR
REF )
where
- y: PLL index (1 or 2)
- DPLLy_FDEV: Frequency deviation value (0 to 238–1)
- Reqd_ppb: Required DCO frequency step size (in ppb)
- DENREF: REF-DPLLy feedback divider denominator value (1 to 240)
- fINx: Reference input frequency (x = 0, 1, 2, 3)
- RINx: Reference input divide value (1 to 216–1) (x = 0, 1, 2, 3)
- fVCOy: VCOy frequency
- P1PLLy = PLLy primary post-divide value (4 to 9, 11, 13)
- PRREF: REF-DPLLy feedback prescaler divide value (2 to 17)
Equation 17 shows the formula to compute the DPLLy_FDEV register value required to meet the specified DCO frequency step size (in ppb) when DCO mode is enabled for the TCXO-DPLL (when DPLLy_DCO_SEL_REF_TCXOB = 0).
Equation 17. DPLLy_FDEV = ( Reqd_ppb / 10
9 ) × DEN
TCXO / ( f
TCXO × D / M ) × f
VCOy / ( P1
PLLy × PR
TCXO )
where
- DENTCXO: TCXO-DPLLy feedback divider denominator value (fixed, 240)
- fTCXO: TCXO/OCXO input frequency
- DTCXO: TCXO/OCXO input doubler (1 = disabled, 2 = enabled)
- MTCXO: TCXO/OCXO input divide value (1 to 32)
- PRTCXO: TCXO-DPLLy feedback prescaler divide value (2 to 17)