A current limiter for DC/DC regulators with compensation against process and temperature variations

A low-voltage current limiter suitable for both linear and switching regulators is presented. Although the approach relies on absolute values of sense resistance and MOSFET threshold voltage on subsequent I/V and V/I conversions of the sensed current, a reference current in the process and temperature (PT) compensator is derived in such a manner that the dependence of clamping threshold I _TH on PT-spread is first-order canceled out. Furthermore, the current sensor embodies a transconductor build up with either p-MOSFET depletion-mode device or a level-shifter with enhancement-mode transistors, meeting low-dropout requirements. For nominal value of 750 mA, Monte Carlo data express boundaries for I _TH of 523 and 1,075 mA, accounting for broad PT-variation, as well as operating voltages and mismatching. A linear regulator with 400 mA-current rate and 250 mV-dropout incorporating the limiter on its depletion p-MOSFET version was integrated on a smart-power process. The limiter occupies an area of 0.052 mm² and consumes only 65 μA. Experimental data attest the clamper functionality and accuracy against PT-variations. From samples of distinct lots, I _TH spans from 615 to 996 mA. Owing to its simplicity and open-loop operation in case of switchers, the limiter reacts upon overcurrent in only 20 ns, making it compatible with converters functioning in MHz range and under low duty-cycles. Moreover, the limiter suits supply voltages as low as 1 V.