1. Function description
     1. LPTIM outputs PWM signal
2. Use environment
     Software development environment: KEIL MDK-ARM V5.26.2.0
     Hardware environment: Developed based on N32L43XM-STB
3. Instructions for use
     System Configuration;
         1. Clock source:
             HSE=8M, PLL=108M, AHB=108M, APB1=27M, APB2=54M, LPTIM CLK=LSI
         2. Port configuration:
             PC1 is selected as LPTIM output
         3. LPTIM:
             LPTIM 4 frequency division LSI, output PWM signal
     Instructions:
         1. Open the debug mode after compiling, and you can observe the PC1 pin PWM signal
4. Matters needing attention
     without