STMicroelectronics /STM32U545 /RCC /RCC_PLL3FRACR

Fractional part of the multiplication factor for PLL3 VCO This bitfield is set and reset by software to control the fractional part of the VCO multiplication factor. It can be written at any time, allowing dynamic fine-tuning of the PLL3 VCO. VCO output frequency = F_{ref3_ck} x (PLL3N + (PLL3FRACN / 2¹³)), with: PLL3N must be between 4 and 512. PLL3FRACN can be between 0 and 2¹³ - 1. The input frequency F_{ref3_ck} must be between 4 and 16 MHz. In order to change the FRACN 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.