Project Analog - February 2009 - (Page 16) figurE 1 aN EvaluaTioN BoarD WiTh aN EighT-PhasE DEsigN hElPs oPTimizE PoWEr coNsumPTioN WiThouT chaNgiNg ExTErNal comPoNENTs. recently took on this task. These new devices integrate innovative digital technology into mixed-signal multiphase synchronous buck controllers to manage core voltage and load requirements in VR11.x processors, GPUs, and memory modules. By taking advantage of these new digital control techniques, these new controllers promise to significantly boost efficiency, increase performance, reduce thermal management issues, improve monitoring and control, and reduce component count. One way these new controllers improve power efficiency is by using an architecture comprised of up to eight interleaved synchronous buck phases. Currently available controllers typically offer four or, in a few exceptions, six phase control. By allowing designers to digitally configure the switching frequency of up to eight phases and storing those parameters in nonvolatile memory, these new devices can be used to optimize power consumption without altering external components. In addition, by spreading the power across a larger number of phases, designers can use smaller inductors, saving precious board space, and gain faster transient response. An evaluation board has an eight-phase design shown in Figure 1. But these new controllers don’t just increase the number of phases. They also add the ability to shed or turn off phases as current drops. Moreover, a new adjustable gate drive capability allows designers to reduce MOSFET gate drive voltage in low current conditions. Using eightphase capability for high-current conditions, and phase shedding and adjustable gate drive innovations for mid-to low current conditions, these new buck controllers are the first to offer over 90% power efficiency across virtually all load conditions. Figure 2 shows a model of the efficiency gains from the use of phase shedding and variable gate drive in comparison to 9- and 12-V fixed-drive designs. In addition, Figure 3 displays the measured efficiency of an eight-phase design transitioning to six phases and one phase (1.4-V output, 300-kHz Contents Viewpoint Selecting the Right dc/dc Converter Selecting the Right Battery System Understanding the Buck Switchmode Power Converter Analog news Microchip analog page Sample center microchipDIRECT Reference designs/ app notes Technical training figurE 2 PhasE shEDDiNg aND variaBlE gaTE DrivE EfficiENcy gaiNs arE comParED To fixED DrivE DEsigNs. 16 · PRojeCt ANAlog · VolUme 3 / NUmBeR 1 http://www.microchip.com http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=79&redirects=analog http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=79&redirects=analog http://sample.microchip.com/Default.aspx?testCookies=true http://www.microchipdirect.com/catalogselection.aspx?returnURL=default.aspx http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1469&filter1=function&redirects=appnotes http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1469&filter1=function&redirects=appnotes http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1423
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