Low power mode detection circuit for a DC/DC converter

A DC/DC converter for generating a voltage at an output which is lower than a voltage supplied to an input comprising:

• an NMOS transistor coupled between the voltage supply and the series connection of an inductor and a capacitor, voltage across the capacitor being the output voltage;
• an NMOS synchronous rectifier transistor connected in parallel to the series connected inductor and capacitor, the synchronous rectifier having a parasitic diode coupled in parallel thereto;
• a control circuit coupled to the NMOS transistor and the NMOS synchronous rectifier transistor and providing a drive signal between substantially the supply voltage and substantially a reference voltage;
• and
• a voltage detector circuit coupled across the NMOS synchronous rectifier transistor detecting polarity of a voltage across the NMOS synchronous rectifier transistor and generating a control signal to place the converter in a low power mode when the polarity across the synchronous rectifier indicates that reverse current flow is possible.

A voltage converter comprising:

• a first switching transistor coupled to a first voltage supply, an inductor, and a capacitor, voltage across the capacitor being an output voltage;
• a rectifier coupled to the inductor to allow a collapse of the magnetic field of the inductor to charge the capacitor;
• a voltage comparator coupled across the rectifier and detecting a polarity of voltage across the rectifier;
• a control circuit responsive to an output of the voltage comparator indicative of a polarity reversal across the rectifier during the decay of the inductor magnetic field, to generate a control signal which places the voltage converter in a low power mode.