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

Abstract

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 mm 2 and consumes only 65 lA. 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 dutycycles. Moreover, the limiter suits supply voltages as low as 1 V.

An improvement of the current–voltage conversion technique in over-current sensing circuit for low-power low dropout linear voltage regulators

“…Although the results in the [3,8,9] are obtained from experiment measurements, and the results in this paper are only acquired from the simulations. However, based on the Monte Carlo analysis, the worst case of this work which is shown in Fig.…”