Using Power Delivery Path Resistance For Precision CPU Current Monitoring

Focus:

To monitor CPU current (and power), typical CPU voltage regulator (VR) designs use the VR inductor’s winding equivalent series resistance (ESR) and/or VR switching transistor’s on- resistance as current sensors. When processor current is constant or varies slowly, the inductor current (or MOSFET current magnitude) signal practically replicates the CPU current waveform and such sensing techniques provide reasonable accuracy. But in very dynamic modes with high current slew rates, the effect of LC-filtering results in latencies and level errors. This article describes a current monitoring technique that addresses this issue by performing nonintrusive, real-time current monitoring of the actual CPU current. The article begins by discussing the threat posed by power viruses, and why this requires power monitoring at the point of load. Then the current monitoring concept is explained: CPU current can be derived as a sum of the currents flowing through the power plane and cavity cap array. Models of the power delivery network are presented, sources of error are discussed, details of implementation are explained, and experimental results are presented to verify the technique.

What you’ll learn:

• How to perform nonintrusive, real-time current monitoring of CPU current
• How to overcome errors in CPU current monitoring due to effects of LC filtering

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Author & Publication:

Viktor Vogman, Power Conversion Consulting, Olympia, Wash., How2Power Today, Feb 15 2019

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