An arrangement for measuring current through a phase section of a buck mode DC-DC
converter includes an auxiliary integrated circuit containing an auxiliary power
MOSFET and a pilot MOSFET coupled in parallel with a current path through a high
side MOSFET of a half-bridge of the converter. The pilot MOSFET has a current path
coupled to a current measurement terminal. The MOSFETs of the auxiliary circuit
are time division multiplexed with the high side MOSFET, whereby a determination
of current through the auxiliary high side MOSFET is based upon current through
the pilot device and the geometric ratio of the size of the pilot device to that
of the high side auxiliary MOSFET. The high side MOSFET is activated for a large
number of switching cycles relative to the pilot circuitry, but the pilot circuitry
is activated sufficiently often to derive a relatively accurate measure of current flow.
