A Simple Sensorless Current Sharing Technique for Multiphase DC-DC Buck Converters

Multiphase buck converters are widely used to power up low-voltage high-current loads, such as microprocessors, battery chargers, hybrid vehicles, among others. For this converter, topology is necessary to guarantee a correct distribution of the total output current among phases in order to ensure proportionality in electrical losses and thermal stresses. So, a current sharing scheme is a desirable part in a multiphase buck converter. Most of the proposed current distribution schemes include sensing circuitry and a current loop for each phase. Nevertheless, by using sensors, control complexity and assembly costs increases proportionally to the number of phases. This paper presents a simple sensorless current sharing algorithm for multiphase buck converters. The proposed technique is based on simple one-time tests by turning-on each phase in order to estimate the parasitic resistance for the turned-on phase. Once the parasitic resistances are known, the duty cycles, which allow for adequate current sharing among phases, are calculated. An extra control algorithm ensures that the compensated duty cycle is applied at the switching node. This extra control loop does not require analog-to-digital converters. Analysis and experimental results of proposed control technique are shown using a five-phase dc-dc buck converter. The proposed algorithm exhibits an adequate distribution of the load current between phases.