High bandwidth constant on-time PWM control

A method to dynamically adjust bandwidth in a variable frequency modulation control circuit, the method comprising:

• provide a feedback control circuit configured to generate a control output signal from both a predetermined reference and a control input signal, wherein the control input signal corresponds to a pulse-width modulated output delivered to a load through an inductor;
• provide a frequency modulation circuit configured to generate, in response to a frequency control input signal, a frequency control output signal corresponding to a switching frequency of at least one switch circuit, wherein the switch circuit is configured to generate the pulse-width modulated output;
• generate from the control output signal of the frequency modulation circuit a transient control signal in response to a transient in the frequency control output signal;
• and,
• apply the transient control signal to the control output signal to generate a frequency control input signal,
• wherein the transient control signal is generated such that the frequency control input signal causes the frequency modulation circuit to maintain a predetermined relationship between the switching frequency and a crossover frequency, where the crossover frequency corresponds to a frequency of a closed-loop circuit at unity gain, the closed-loop circuit including at least the feedback control circuit and the frequency modulation circuit.

A variable frequency modulation control circuit comprising:

• a feedback control circuit configured to generate a control output signal from both a predetermined reference and a control input signal, wherein the control input signal corresponds to a pulse-width modulated output delivered to a load through an inductor;
• a frequency modulation circuit configured to generate, in response to a frequency control input signal, a frequency control output signal corresponding to a switching frequency of at least one switch circuit, wherein the switch circuit is configured to generate the pulse-width modulated output;
• means for generating from the control output signal of the frequency modulation circuit a transient control signal in response to a transient in the frequency control output signal;
• and,
• means for applying the transient control signal to the control output signal to generate the frequency control input signal,
• wherein the means for generating the transient control signal is configured to generate the transient control signal such that the frequency control input signal causes the frequency modulation circuit to maintain a predetermined relationship between the switching frequency and a crossover frequency, where the crossover frequency corresponds to frequency of a closed-loop circuit at unity gain, the closed-loop circuit including at least the feedback control circuit and frequency modulation circuit.