Slope compensation module

A switched-mode power supply (SMPS) controller having a slope compensation module, comprising:

• a voltage reference;
• an error amplifier coupled with the voltage reference and comprising an output;
• and
• a voltage comparator comprising a first input;
• a slope compensation module having an input coupled to an output of the error amplifier, and an output, wherein the slope compensation module comprises:
• a slope compensation capacitor coupled between the output of the error amplifier and the first input of the voltage comparator;
• a slope compensation switch coupled in parallel with the slope compensation capacitor;
• and
• a programmable constant current source coupled to an output side of the slope compensation capacitor;
• wherein a second input of the voltage comparator is adapted for coupling to a current-to-voltage circuit that measures a current signal;
• a period generator;
• and
• a reset dominant latch comprising
• a set input coupled to an output of the period generator,
• a reset input coupled to an output of the voltage comparator, and
• an output that is coupled to and controls opening and closing the slope compensation switch,
• the output of the reset dominant latch also provides a control signal;
• the period generator provides a plurality of pulses at a pulse period to the set input of the reset dominant latch, wherein each time a pulse is received at the set input of the reset dominant latch the output thereof goes to a second logic level from a first logic level;
• when the output of the reset dominant latch is at the second logic level the slope compensation switch opens and the slope compensation capacitor charges through the programmable constant current source to a circuit common, thereby generating a linearly decreasing ramp voltage for modulating a feedback error voltage from the error amplifier into a slope compensated feedback error voltage;
• when the slope compensated feedback error voltage that is coupled to the first input of the voltage comparator is less than a voltage representing the current through the SMPS inductor at the second input of the voltage comparator, the output of the reset dominant latch returns to the first logic level and the slope compensation switch closes thereby discharging the slope compensation capacitor and returning the first input of the voltage comparator to the feedback error voltage from the error amplifier.

An analog pulse width modulation (PWM) generator, comprising:

• a capacitor having an input coupled to a first voltage reference;
• a switch coupled in parallel with the input and an output of the capacitor;
• a programmable constant current source coupled to the output of the capacitor;
• a first voltage comparator having a first input coupled to the output of the capacitor, a second input coupled to a second voltage reference and an output that controls opening and closing of the switch;
• a second voltage comparator having a first input coupled to the output of the capacitor, a second input adapted for coupling to a voltage from a switched-mode power supply (SMPS) and an output that provides a pulse width modulated (PWM) control signal for controlling a power switch of a switched-mode power supply;
• wherein when a voltage at the output of the capacitor is less than a voltage from the first voltage reference the switch will open, whereby the capacitor and the programmable constant current source modulate a voltage from the first voltage reference with a linear negatively sloping voltage waveform;
• wherein a voltage difference between the first and second voltage references determines a period of the PWM control signal, and a voltage difference between the voltage from the SMPS and the voltage at the second node of the capacitor determines a duty cycle of the PWM control signal.

A method for providing slope compensation in a switched-mode power supply (SMPS) controller comprising an error amplifier with an output, a voltage comparator with a first input, a slope compensation capacitor coupled between the output of the error amplifier and the first input of the voltage comparator, a slope compensation switched coupled in parallel with the slope compensation capacitor, and a programmable constant current source coupled to an output side of the slope compensation capacitor and to the slope compensation switch, said method comprising the steps of:

• providing a reference voltage;
• comparing the reference voltage to output feedback voltage from the SMPS controller with the error amplifier that provides an error voltage that is the difference between the reference voltage and the voltage from the SMPS filter network;
• comparing a slope compensated error voltage from the slope compensation capacitor to a voltage representation of current measured in a SMPS inductor;
• providing a reset dominant latch having a set input coupled to an output of a period generator, a reset input coupled to an output of the voltage comparator, and an output that controls opening and closing of the slope compensation switch and for supplying a control signal;
• and
• providing a plurality of pulses at a pulse period from the period generator to the set input of the reset dominant latch, wherein each time a pulse is received at the set input of the reset dominant latch the output thereof goes to a second logic level from a first logic level;
• opening the slope compensation switch when the output of the reset dominant latch is at the second logic level;
• generating a linearly decreasing ramp voltage for modulating the feedback error voltage from the error amplifier into a slope compensated feedback error voltage;
• and
• returning the output of the reset dominant latch to the first logic level and closing the slope compensation switch when the slope compensated error voltage is less than the voltage representing the current through the SMPS inductor.