Four-Terminal Inductor Achieves High-Accuracy Current Measurements For POLs (Part 1): Inductor Design

by Ron Vinsant, Vishay Siliconix, Santa Clara, Calif. , How2Power Today, Feb 16 2016

Focus:
This is the first of a three-part series that will discuss the application of a single-phase synchronous rectifier capable of high currents and high efficiency combined with a four-terminal inductor used for sensing output current via the DCR of the coil. The focus here will be on current accuracy. The four-terminal inductor is based on a novel construction that allows a close tolerance on DCR and little drift with temperature. These performance parameters are used by the POL regulator’s A-D converter to allow a highly accurate read back of output current that maintains its accuracy over temperature and time. In this first segment, the four-terminal inductor and its use in measuring current are discussed. An example inductor test circuit is presented, selection of an RC pair to match the L-DCR time is discussed, the impact of the inductance tolerance on the time constant matching and accuracy of the current-sense voltage is simulated, the impact of inductor nonlinearity is discussed, and a three current probe technique for testing inductor operation is shown.

What you’ll learn:

• How to understand the benefits of a novel four-terminal inductor for current sensing in high-current, point-of-load regulators

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