Multi-mode controlled power converter

1. A switched power converter comprising a switchable power stage for generating an output voltage according to a switching signal and an input voltage via a switching element, the switching signal being generated by a multi-mode controller, said multi-mode controller controlling a digital control path for generating a pulse width modulation switching signal and a constant-on-time control path for generating a constant-on-time switching signal, wherein the switching signal for controlling the switching element is generated in the digital control path when the multi-mode controller is run in a high load mode and wherein the switching signal is generated in the constant-on-time control path when the multi-mode controller is run in a light load mode, and wherein the digital control path is disconnected from power supply when the multi-mode controller is run in light load mode, wherein the constant-on-time control path further comprises a minimum-off-time circuit configured to compute a sum of constant-on-time and a minimum-off-time, and wherein the multimode controller is configured to activate the digital control path when the sum of the constant-on-time and the minimum-off-time is not greater than a normal period of the pulse width modulation switching signal.

2. The switched power converter according to claim 1 , wherein the multi-mode controller is configured to determine executing the light load mode or the high load mode from a load current or by monitoring the output voltage.

3. The switched power converter according to claim 1 , wherein the digital control path comprises an error amplifier for amplifying a difference between the output voltage and a reference voltage for generating an error signal; an analog to digital converter to convert the error signal into a digitized error signal; a PID compensator to generate a pulse width modulation duty cycle according to the digitized error signal; and digital pulse width modulator for generating the pulse width modulation switching signal.

4. The switched power converter according to claim 3 , wherein the error amplifier, the analog to digital converter, the PID compensator and the digital pulse width modulator are adjustable with respect to bandwidth by the multi-mode controller.

5. The switched power converter according to claim 1 , further comprising a multiplexer for multiplexing the switching signal between the constant-on-time switching signal and the pulse width modulation switching signal, said multiplexer controlled by the multi-mode controller.

6. The switched power converter according to claim 1 , wherein the constant-on-time path comprises a comparator and a constant-on-time circuit, wherein the comparator is configured to compare the output voltage with a reference voltage and wherein the comparator is connected to the multi-mode controller and the constant-on-time circuit.

7. The switched power converter according to claim 1 , wherein the switchable power stage comprises a third switching element to short-circuit an inductor for draining an excessive inductor current.

8. The switched power converter according to claim 1 , further comprising a driver with zero current detection to drive the switching element according to the switching signal.

9. A method for controlling a switched power converter comprising a switchable power stage switched according to a switching signal, the method comprising:

generating a pulse width modulation switching signal in a digital control path when running the switched power converter in a high load mode;

disconnecting the digital control path from a power supply, and generating a constant-on-time switching signal in a constant-on-time control path when running the switched power converter in a light load mode;

computing a sum of constant-on-time and a minimum-off-time with a minimum-off time circuit in the constant-on-time control path; and

activating the digital control path when the sum of the constant on-time and the minimum off-time determined in the constant-on-time control path is not greater than a normal period of the pulse width modulation switching signal.