Full-time inductor current monitoring method by sensing low side switch

An inductor current sensing device for detecting an inductor current in a Switch Mode Power Supply (SMPS), wherein the SMPS has a high-side (HS) switch and a low-side (LS) switch coupled in series and an output filter including an inductor and a capacitor coupled to a switch node formed by the HS and LS switches, wherein an inductor current is supplied by the inductor to a load, the inductor current sensing device comprising:

• a current sensing circuit coupled across the LS switch, the current sensing circuit configured to sense a current across the LS switch and generate a sensed current, wherein the sensed current includes a first current slope and a minimum current value,
• a slope sensing circuit coupled to the current sensing circuit, the slope sensing circuit having a first input configured to receive the sensed current from the current sensing circuit, wherein the slope sensing circuit is configured to convert the first current slope in the sensed current into a first constant DC slope information;
• an operator circuit coupled to the slope sensing circuit, the operator circuit having a first input configured to receive the first constant DC slope information from the slope sensing circuit, a second input configured to receive an input voltage VIN of the SMPS and a third input to receive an output voltage VOUT of the SMPS, wherein the operator circuit is configured to generate a second constant DC slope information based on the first, second and third inputs;
• and
• a current slope synthesis circuit coupled to the operator circuit and the slope sensing circuit, the current slope synthesis circuit having a first input configured to receive the first constant DC slope information, a second input configured to receive the second constant DC slope information and a third input configured to receive a control signal, wherein the current slope synthesis circuit is configured to generate a synthesis signal by integrating the first and second constant DC slope information according to the control signal, wherein the synthesis signal has a triangular waveform including a rising slope when the control signal is in a first state and a falling slope when the control signal is in a second state opposite to the first state, wherein the rising and falling slopes of the synthesis signal are respectively proportional to rising and falling slopes of the inductor current.

A method for sensing an inductor current in a Switch Mode Power Supply (SMPS), wherein the SMPS has a high-side (HS) switch and a low-side (LS) switch coupled in series and an output filter including an inductor and a capacitor coupled to a switch node formed by the HS and LS switches, wherein an inductor current is supplied by the inductor to a load, the method comprising:

• generating a sensed current by sensing a current across the LS switch, wherein the sensed current includes a first current slope and a minimum current value;
• converting the first current slope in the sensed current into a first constant DC slope information;
• generating a second constant DC slope information based on the first constant DC slope information, an input voltage VIN of the SMPS and an output voltage VOUT of the SNIPS;
• and
• generating a synthesis signal by integrating the first and second constant DC slope information according to a control signal, wherein the synthesis signal has a triangular waveform including a rising slope when the control signal is in a first state and a falling slope when the control signal is in a second state opposite to the first state, wherein the rising and falling slopes of the synthesis signal are respectively proportional to rising and falling slopes of the inductor current.

A slope sensing device for sensing a slope of an input signal and providing an output signal proportional to the input signal, the slope sensing device comprising:

• a differentiator having an input configured to receive an input signal having a triangular waveform with at least one slope, wherein the differentiator is configured to generate a differentiated signal by differentiating the input signal using a first capacitor and;
• a sample and hold circuit having a first input configured to receive the differentiated signal and a second input to receive a triggering signal, wherein the sample and hold circuit is configured to convert the differentiated signal into a constant DC slope information by sampling and held the differentiated signal when the triggering signal is on;
• and
• an integrator having an input configured to receive the constant DC slope information, wherein the integrator is configured to generate an output signal having a waveform proportional to the waveform of the input signal by using a second capacitor.