Method and circuit of soft start and of power monitor for IC with multiple supplies

#The present invention relates to integrated digital circuits, and, more particularly, to a procedure for monitoring all the power supplies within an integrated circuit (IC). This monitoring is a function referred to as power monitoring.

#Integrated systems tend to have several subsystems and power sections integrated on a single chip. These devices commonly use different positive power supplies, and often use negative power supplies to power in the most efficient manner the different chip sections or the various subsystems integrated on the same chip.

#Sometimes one or more supply voltage sources are externally provided, while others are implemented internally by as many voltage regulators as there are externally generated supply voltages. In these monolithic integrated complex systems, it is very important to monitor the level of all the different supply voltages and to generate a so-called NPOR signal stating their compliance or noncompliance with their respective design values.

#FIG. 1 is a sequence of diagrams depicting the turn-on procedure for a positive verification of the internally generated supply voltages according to the present invention;

#FIG. 2 is a sequence of diagrams depicting the turn-on procedure for a negative verification of the internally generated supply voltages according to the present invention; and

#FIG. 3 is a basic block diagram for implementing the method according to the present invention.

#The system of the present invention has been successfully tested in an integrated circuit (IC) having a plurality of regulators therein. In a sample device, a first supply voltage 12V and a second supply voltage 5V are applied to respective pins from external sources. A third supply voltage 3.3V is generated internally and powers a regulator generating a fourth regulated supply voltage 2.5V and a regulator generating a fifth negative supply voltage −5V.

#The basic diagram of a circuit according to the present invention is depicted in FIG. 3. FIGS. 1 and 2 illustrate a sequence of diagrams (corresponding to an algorithm) depicting the turn-on procedures for two different situations that may occur at the turn-on of the IC.

#Referring to the diagram of FIG. 3, both the soft start function and the power monitor function are implemented according to the present invention via a single external capacitor C. The use of a single external capacitor requires only one pin of the IC. The capacitor C is charged by the current generator I towards a certain voltage, which is indicated as Vreg. At turn-on, the transistor M1 is biased in a conduction state so that the external capacitor C maintains in a discharged state.