Method and apparatus for phase current balancing in multi-phase constant on-time buck converter

A method in a multi-phase DC-to-DC buck converter for receiving an input voltage and delivering an output voltage to a load by splitting the load current between a plurality of DC-to-DC buck converter cells, the method comprising:

• sensing current in a respective one of the plurality of converter cells and generating a respective current sense signal;
• receiving each of the respective current sense signals and generating an average signal;
• comparing a respective current sense signal with the average signal and generating a respective current imbalance signal;
• and
• activating a respective one of the plurality of converter cells for a predetermined time interval and altering the predetermined time interval in accordance with a time integral of a respective current imbalance signal.

A multi-phase DC-to-DC buck converter for receiving an input voltage and delivering an output voltage to a load by splitting the load current between a plurality of DC-to-DC buck converter cells, the converter comprising:

• a plurality of current sense circuits each configured to sense current in a respective one of the plurality of converter cells, each of the plurality of current sense circuits configured to generate a respective current sense signal;
• an averaging circuit configured to receive each of the respective current sense signals and generate an average signal;
• a plurality of imbalance detector circuits each configured to compare a respective current sense signal with the average signal and generate a respective current imbalance signal;
• a plurality of transconductor circuits, wherein each of the plurality of transconductor circuits is configured to transform a respective current imbalance signal to current;
• a plurality of multiplier-divider circuits, wherein each of the plurality of multiplier-divider circuits is configured to multiply a respective current imbalance signal by a ratio of the input voltage and the output voltage, and to generate a normalized current imbalance signal;
• and
• a plurality of ON time generators each configured to activate a respective one of the plurality of converter cells for a predetermined time interval and to alter the predetermined time interval in accordance with a time integral of a respective normalized current imbalance signal;
• each of the ON time generators comprising:
• a source of predetermined current;
• a timing capacitor configured to integrate a sum of the predetermined current and a respective current imbalance signal and generate a ramp voltage;
• and
• a comparator for terminating the altered predetermined time interval upon the ramp voltage exceeding a threshold.

A multi-phase DC-to-DC buck converter for receiving an input voltage and delivering an output voltage to a load by splitting the load current between a plurality of DC-to-DC buck converter cells, the converter comprising:

• a plurality of current sense circuits each configured to sense current in a respective one of the plurality of converter cells, each of the plurality of current sense circuits configured to generate a respective current sense signal;
• an averaging circuit configured to receive each of the respective current sense signals and generate an average signal;
• a plurality of imbalance detector circuits each configured to compare a respective current sense signal with the average signal and generate a respective current imbalance signal;
• a plurality of transconductor circuits, wherein each of the plurality of transconductor circuits is configured to transform a respective current imbalance signal to current;
• a plurality of multiplier circuits, wherein each of the plurality of multiplier circuits is configured to multiply a respective current imbalance signal by a duty cycle of a respective one of the plurality of DC-to-DC buck converter cells, and to generate a normalized current imbalance signal;
• and
• a plurality of ON time generators each configured to activate a respective one of the plurality of converter cells for a predetermined time interval and to alter the predetermined time interval in accordance with a time integral of a respective normalized current imbalance signal;
• each of the ON time generators comprising:
• a source of predetermined current;
• a timing capacitor configured to integrate a sum of the predetermined current and a respective current imbalance signal and generate a ramp voltage;
• and
• a comparator for terminating the altered predetermined time interval upon the ramp voltage exceeding a threshold.