fractional part of the multiplication factor for PLL3 VCO
Set and reset by software to control the fractional part of the multiplication factor of the VCO. These bits can be written at any time, allowing dynamic fine-tuning of the PLL3 VCO.
The software must set correctly these bits to insure that the VCO output frequency is between its valid frequency range, that is:
- 128 to 560 MHz if PLL3VCOSEL = 0
- 150 to 420 MHz if PLL3VCOSEL = 1
VCO output frequency = Fref3_ck x (PLL3N + (PLL3FRACN / 213)), with
- PLL3N between 8 and 420
- PLL3FRACN can be between 0 and 213- 1
- The input frequency Fref3_ck must be between 1 and 16 MHz.
To change the PLL3FRACN value on-the-fly even if the PLL is enabled, the application must proceed as follows:
- Set the bit PLL3FRACEN to 0
- Write the new fractional value into PLL3FRACN
- Set the bit PLL3FRACEN to 1.