Low-voltage High-current Multi-phase Digital Dc-dc Converter

Digital Power has been paid much attention in recent years because of their universal, flexibility and programmable characteristics. On the other hand, with the rapid progress on microprocessors, the challenge for low voltage high current VRM design has increased. In this paper, the digital control method is applied to the VRM design, and some meaningful work has been done in both system modeling and circuit implementation.First, the multiphase buck DC-DC converter is analyzed in system level. After the power stage is modeled, a digital PID controller is derived, and the AVP is achieved in voltage control mode. Simulink is used to model and simulate the controller's behavior. The simulated results demonstrate that AVP control improve the dynamic performance of the converter.Then, the design of sub-modules is discussed in detail. By following the standard ASIC design flow, the controller's circuit and layout is implemented. A full custom buck driver circuit is designed, and a MOS-only voltage reference and a clock generator based on current driver delay cell are proposed, the voltage reference was implemented with Chartered 0.35um CMOS process and had been tested.At last, a complete Voltage Regulator Module is designed, with the controller implemented by FPGA, and the driver and ADC integrated on board. Under the 12V ATX power input and at the switch frequency of 1MHz, the converter's output voltage is 0-1. 6V, identified by 8 bit VID code. The startup time is less than 1ms, and the set point error and voltage ripple are both below 10mV. When the load current has a step transit of 40A, the output voltage changes about 80mV. The experimental results coincide with the expected specification.Finally, the whole design work is concluded and some further research directions are given.