Voltage regulators often have coupled output inductors because coupled
output inductors provide improvements in cost and efficiency. Coupled
inductors are often used in multi-phase voltage regulators. Feedback
control of voltage regulators often requires accurate and responsive
sensing of output current. Provided is a technique for accurately sensing
the magnitude of output current in coupled inductors. An RC circuit
(comprising a resistor and capacitor in series) is connected in parallel
with the coupled inductor. The inductor has a leakage inductance Lk and a
DC (ohmic) resistance of DCR. The resistor and capacitor are selected
such that an RC time constant is equal to an L/R time constant of Lk/DCR.
With the matching time constants, a sum of voltages on the capacitors is
accurately proportional to a sum of currents flowing in the output
inductors. Also provided is a technique for sensing current when an
uncoupled center tap inductor is present.