Automatic transition between PFM and PWM modes in a switching regulator

A method of transitioning a switching regulator from a Pulse Width Modulation mode to a Pulse Frequency Modulation mode, the method comprising:

• determining a current threshold setting for a load current and a pulse filter trip point, wherein the current threshold setting is determined to be one of an upper threshold and a lower threshold, and wherein the switching regulator is in the Pulse Width Modulation mode when the load current is above the upper threshold;
• measuring a dead-time of the switching regulator to estimate the load current in the Pulse Width Modulation mode;
• and
• transitioning to the Pulse Frequency Modulation mode, when the dead-time is greater than the pulse filter trip point, for estimating the load-current, wherein the load current is estimated in the Pulse Frequency Modulation mode by deriving a slope of a waveform of an output voltage of the switching regulator during the dead-time, and wherein the pulse filter trip point is modified to increase the dead-time after tentative transition to the Pulse Frequency Modulation mode.

A circuit for automatically transitioning from a Pulse Width Modulation mode to a Pulse Frequency Modulation mode and vice-versa, the circuit comprising:

• a zero crossing detector configured to receive a voltage from a switching regulator;
• a multiplexer configured to receive a control signal for selecting a pulse filter trip point from a plurality of pulse filter trip points;
• a pulse filter configured to receive outputs of the zero crossing detector and the multiplexer configured for selecting the pulse filter trip point, wherein the pulse filter measures a duration of dead-time in an output voltage of the switching regulator, based on the outputs of the zero crossing detector and the multiplexer configured for selecting the pulse filter trip point;
• a current sense circuit configured to receive a voltage from an LC filter circuit, wherein the voltage from the LC filter circuit is dependent on the output voltage of the switching regulator, and wherein an output of the current sense circuit is indicative of a load current of the switching regulator;
• a multiplexer configured to receive a control signal for selecting a current threshold setting, wherein the current threshold setting is selected as one of an upper threshold and a lower threshold;
• a current comparator circuit configured to compare outputs of the current sense circuit and the multiplexer configured for selecting the current threshold setting;
• and
• a digital control logic configured to:
• provide control signal to the multiplexer configured for selecting the pulse filter trip point;
• provide control signal to the multiplexer configured for selecting the current threshold setting;
• and
• generate a mode select signal for selecting one of a Pulse Width Modulation mode and a Pulse Frequency Modulation mode of operation, wherein the digital control logic generates the control signals and the mode select signal based on outputs of the pulse filter and the current comparator circuit.