Investigation On Transient Response Performance Of Point-Of-Load (POL) Converter

As the core voltage of microprocessor reduced to less than 1V and the core static current is still increasing, higher efficiency, higher power density, faster transient response and lower cost are required for future Point-Of-Load (POL) converter. In general, the research on transient response performance of POL converter purely focused on either the power stage or control strategy. However, this research project comprehensively considers the function of power stage in combination with control mode. This thesis presents a design example of a 12V input, 0.9V-3.3V adjustable output voltage with 16A maximum current POL converter, which adopts the synchronous BUCK topology and mainly covers following topics:Firstly, this thesis reviews the analysis and design of POL converter power stage. It is discussed how to choose main components, including high-side and low-side MOSFET, filter inductor in order to achieve comparatively high efficiency.Secondly, those factors contributing to transient response performance of POL converter, the value of inductor, the moment when the load-current changes, the performance of output capacitor and controller are described in detail. It is also discussed how to choose the LC filter with Mathcad software.Meanwhile, this thesis proposes a new design method to achieve Adaptive Voltage Positioning (AVP) Control, whose voltage amplifier compensation network is resistive feedback. The control loop design procedure in both large signal and small signal system is also presented. By introducing a DC gain in the voltage loop, the output voltage will not return to original value after transient response, as such, the overshoot and undershoot will be reduced. It is also analyzed in depth how to design programmable output voltage POL converter with Average Current Control to optimize the system performance. On the basis of above analysis, this thesis compares the pros and cons of both Average Current Control Mode and Finite DC Gain AVP Control, which are proved by PSpice simulation.Finally, a high power density POL converter (compliant with DOSA converter standard) is designed and the experiment results prove the aforementioned analysis.This research project on transient response performance of POL converter indicated that a programmable output voltage POL converter with good AC dynamic accuracy can be designed by selecting appropriate power stage parameters and control mode.