Design Of CPU Core Power Supply For Notebook Computer

DC-DC converters are widely used in consumer electronic equipment like notebook computers,provide stable power supply for each module.Typically,DC-DC converter control IC manufacturers offer chip SPICE models to facilitate designers to evaluate the performance of power supply system in advance.But most SPICE simulators cannot simulate the physical effects of the layout,so designers could not anticipate layout parasitic effects impact on performance.In addition,in the context of strict cost control,how to design optimized to reduce component quantity or cost are also things designers need to consider in advance during the design phase.CPU core power supply system was chosen as the study object of this thesis,because it's a typical and complex system in laptop power supplies.The thesis focused on studying PDN(power delivery network)effects impact on the stability and the closed-loop output impedance of CPU power supply,also focused on optimizing design method of output capacitors.This paper selected Intel's Broadwell platform CPU to design and optimize the CPU core power supply system to meet Intel's IMVP(Intel Mobile voltage Positioning)specification requirements.Intel's IMVP specification is based on the principle of EAVP(Extended adaptive voltage Positioning),and a tailored specification for Intel CPU core power supply.The Intersil Company's ISL95813 was chosen in this paper as power supply chip to meet the IMVP specification.ISL95813 is working based on Intersil's R3(Robust Ripple Regulator)technology.The R3 modulator as an improved hysteresis current control modulator,has many advantages compared to traditional modulators.These include faster transient settling time,and higher control accuracy.Firstly,small-signal model and average model of VRM(Voltage Regular Module)controller were established by analyzing the behavior of each sub-circuit of VRM theoretically.Based on the small-signal diagram,the transfer function of open-loop gain and closed-loop output impedance were calculated.By further simplifying analysis,the key factors affecting the output impedance and phase margin,as well as an equivalent four-element model of VRM were found.Using result of theoretical analysis,the parameters design of main components of VRM was completed.The average model was used in HSPICE simulation combined with the S-parameters of PDN extracted by electromagnetic simulation tools to reveal the differences of system stability and closed-loop output impedance if considering PDN effects or not,design parameters were adjusted on the basis of this.Optimization of output capacitors was done by using Sigrity OptimizePI software,with VRM equivalent four-element model.Depending on the target impedance,a quantity and layout location optimized scheme of output capacitors was calculated.Finally,the measured test results showed that the average model of the power chip built in this thesis is accurate and credible,and the measured results of optimized CPU core power supply fitted well with the optimized simulation results,and were better than design specification requirements.Design and optimization process described in this thesis has been applied to the CPU core power supply design of several notebook models.Same design and optimization method also can be used on other DC-DC converter designs,facilitate the synergy of power engineers and power integrity engineer on predicting physical PDN impact on power system performance effectively.Meanwhile,according to the specific target of optimization,a reasonable optimization of the output capacitors could be done.