Temperature and supply voltage independent DC-DC current sensing

#The present document relates to a current sensing circuit. In particular, the present document relates to a current sensing circuit which provides reliable indications of the current through a transistor.

#Power converters and in particular switched mode power converters typically make use of one or more power switches which are commutated between an on-state and an off-state in an alternating manner at a commutation cycle rate. The one or more power switches may be controlled in dependence of the current flowing through the one or more power switches. By way of example, a power switch may be commutated from an on-state to an off-state, subject to the detection that the current through the power switch has reached a pre-determined peak current.

#In order to be able to accurately control the states of a power switch based on the current flowing through the power switch, current measurement means are desirable which are configured to provide an accurate indication of the current flowing through the power switch. Such an indication should be substantially independent of the operational conditions of the power switch, such as the temperature and/or the supply voltage at which the power switch is operated. The present document describes such current measurement means (also referred to herein as current sensing circuits).

#The invention is explained below in an illustrative manner with reference to the accompanying drawings, wherein

#FIG. 1 shows a circuit diagram of a power switch and an example current sensing circuit;

#FIGS. 2a and 2b show circuit diagrams of a power switch and an example current sensing circuit which exhibits increased reliability with regards to changing operational conditions of the power switch;

#As outlined above, the present document addresses the technical problem of sensing the current through a power switch in a reliable manner, for different operational conditions of the power switch.

#Current sense circuits may be used in integrated circuits. If a potentially large output current, or load current, is to be driven by an on-chip switch, a current sense circuit may be used to detect the relative or absolute value of this current. The current level may be monitored to prevent damage to the switch, or to the integrated circuit from either a short circuit or an overload. Alternatively or in addition, the current level may be monitored for controlling the switching state of the power switch.

#The power switch may be used e.g. within a buck converter which converts an input voltage to a lower output voltage. The power switch may be implemented as a transistor (e.g. a metal oxide semiconductor, MOS, field effect transistor, FET), which is driven by a pulse-width-modulated control voltage. The switch is turned on and off by the pulse-width-modulated control voltage. As indicated above, it may be important to sense the current through the power switch (when the power switch is turned on) with a minimum efficiency loss, short settling time and good stability against process variations.