Abstract: To reduce the Electro-Magnetic Interference (EMI) impact of the power management unit on other modules of the chip, a Buck converter based on spread spectrum technology is proposed. This converter employs a segmented linear control method to achieve a adjustable switching frequency range, thereby effectively reducing the peak value of the noise spectrum. In addition, an oscillator that is insensitive to process, supply voltage, and temperature variations is designed to ensure the stability of the switching frequency range and reduce output voltage ripple. To enhance system stability, a Type III compensator and power stage driver circuit are also designed. The Buck converter is implemented using a 0.18 μm BCD process, with an input voltage range of 3.5 - 5.0 V and an output voltage of 1.2 V. Simulation results show that the EMI noise spectrum peak value is reduced by 12.13 dB, with output voltage ripple remaining below 10 mV in the 0 - 500 mA load range. The system efficiency reaches a maximum of 84.15%.