Switched power converter with dual mode PWM / COT control
A power converter includes a switched power stage configured to generate an output voltage from an input voltage and a controller configured to generate a pulsed control signal for switching the switched power stage in dependence upon a voltage error signal. The voltage error signal is a difference between a reference voltage and an output voltage. The controller comprises a digital pulse width modulation control path and a digital constant on-time control path. The controller is configured to toggle between a light load mode in which the digital constant-on-time control path is activated and a high load mode in which the digital PWM control path is activated. The constant-on time control path is designed digitally.
1 . A power converter comprising:
a switched power stage configured to generate an output voltage from an input voltage and
a controller configured to generate a pulsed control signal for switching the switched power stage in dependence upon a voltage error signal, the voltage error signal being a difference between a reference voltage and the output voltage;
wherein the controller comprises a digital pulse width modulation control path and a digital constant on-time control path, and wherein the controller is configured to toggle between a light load mode in which the digital constant-on-time control path is activated, and a high load mode in which the digital PWM control path is activated.
2 . The power converter according to claim 1 further comprising an analog to digital converter configured to sample the voltage error signal by employing oversampling at a significantly higher rate compared to a nominal switching rate of a PWM signal generated in the digital PWM control path and configured to provide a digitized voltage error control signal to the digital constant on-time control path and the digital PWM control path.
3 . The power converter according to claim 1 , wherein the digital PWM control path is configured to trigger a restart of a new nominal PWM period of a PWM signal when a threshold based on a duty ratio within a PWM period exceeds a threshold.
4 . The power converter according to claim 3 , wherein the threshold is based on a difference or a derivative of the duty ratio.
5 . The power converter according to claim 3 , wherein the digital PWM control path is configured to prevent a re-occurrence of a restart of the new nominal PWM for a specific period of time.
6 . The power converter according to claims 2 , wherein the constant on-time control path is configured to trigger a pulse of the pulsed control signal when the digitized voltage error exceeds a threshold.
7 . The power converter according to claim 6 , wherein the constant-on time control path comprises a comparator configured to compare the digitized voltage error with a threshold, and configured to trigger a new nominal PWM period according to a sign of the digitized control error.
8 . The power converter according to claim 6 , wherein the constant-on time control path comprises a comparator configured to compare the digitized voltage error with a threshold, and configured to trigger a pulse of pre-set constant on-time according to a sign of the digitized control error.
9 . The power converter according to claim 1 , wherein the controller comprises a comparator to detect when a pre-determined threshold has been exceeded for toggling between the light load mode and the high load mode.
10 . The power converter according to claim 9 , wherein the pre-determined threshold is based on one of current, average inductor current exceeding one half of ripple current value, or voltage.
11 . The power converter according to claim 10 , wherein the pre- determined threshold employs hysteresis.
12 . The power converter according to claim 1 , wherein the controller comprises an adaptive filter configured to determine an optimum point for toggling between the light load mode and the high load mode.
13 . The power converter according to claim 1 , wherein the controller comprises an efficiency estimator configured to determine an optimum point for toggling between the light load mode and the high load mode based on a maximum value of a steady state duty cycle.
14 . The power converter according to claim 1 , wherein the controller is further configured to toggle between phases in a multiphase-configuration by adding or dropping phases.
15 . A control method for a power converter comprising a switched power stage configured to generate an output voltage from an input voltage according to a pulsed control signal controlling a switching of the switched power stage in dependence upon a voltage error signal, the voltage error signal being a difference between a reference voltage and the output voltage, the method comprising:
toggling between a light load mode in which a digital constant-on-time control path is activated and a high load mode in which a digital PWM control path is activated.