Buck DC/DC converter, controller thereof and controlling method thereof, and electronic device

A controller, for a synchronous rectification type buck DC/DC converter including a high-side transistor and a low-side transistor, the controller comprising:

• a pulse modulator, generating a pulse modulation signal, wherein a first level and a second level of the pulse modulation signal are taken such that an output of the buck DC/DC converter is pulse-modulated to approach a target state, the first level instructing the high-side transistor to be turned on and the low-side transistor to be turned off, and the second level instructing the high-side transistor to be turned off and the low-side transistor to be turned on;
• an overcurrent detection circuit, comparing a low-side current flowing through the low-side transistor with a predetermined overcurrent threshold value to generate an overcurrent detection signal that is asserted when the low-side current is greater than the overcurrent threshold value;
• a switch control circuit, at least based on the overcurrent detection signal and the pulse modulation signal, generating a control pulse that takes a first level during a period when the high-side transistor should be on and the low-side transistor should be off, and takes a second level during a period when the high-side transistor should be off and the low-side transistor should be on;
• and
• a driver circuit, driving the high-side transistor and the low-side transistor in response to the control pulse, wherein
• when the overcurrent detection signal is negated, the pulse modulation signal is output as the control pulse,
• when the overcurrent detection signal is asserted, the control pulse is set as the second level,
• when the pulse modulation signal is at the first level and while the overcurrent detection signal is negated, the control pulse is set to the first level during a fixed on time, and
• when the pulse modulation signal is at the second level and while the overcurrent detection signal is negated, the pulse modulation signal is output as the control pulse.

A controlling method for a synchronous rectification type buck DC/DC converter including a high-side transistor and a low-side transistor, the controlling method comprising:

• generating a pulse modulation signal, wherein a first level and a second level of the pulse modulation signal are taken such that an output of the buck DC/DC converter is pulse-modulated to approach a target state, the first level instructing the high-side transistor to be turned on and the low-side transistor to be turned off, and the second level instructing the high-side transistor to be turned off and the low-side transistor to be turned on;
• comparing a low-side current flowing through the low-side transistor with a predetermined overcurrent threshold value to generate an overcurrent detection signal that is asserted when the low-side current is greater than the overcurrent threshold value;
• at least based on the overcurrent detection signal and the pulse modulation signal, generating a control pulse that takes a first level during a period when the high-side transistor should be on and the low-side transistor should be off, and takes a second level during a period when the high-side transistor should be off and the low-side transistor should be on;
• and
• driving the high-side transistor and the low-side transistor in response to the control pulse, wherein
• (i) in a first mode, the control pulse corresponds to the pulse modulation signal, and
• (ii) in a second mode, the control pulse takes the second level for the period during which the overcurrent detection signal is asserted and takes the first level during a fixed on time after the overcurrent detection signal is negated.

A controlling method for a synchronous rectification type buck DC/DC converter including a high-side transistor and a low-side transistor, the controlling method comprising:

• generating a pulse modulation signal, wherein a first level and a second level of the pulse modulation signal are taken such that an output of the buck DC/DC converter is pulse-modulated to approach a target state, the first level instructing the high-side transistor to be turned on and the low-side transistor to be turned off, and the second level instructing the high-side transistor to be turned off and the low-side transistor to be turned on;
• comparing a low-side current flowing through the low-side transistor with a predetermined overcurrent threshold value to generate an overcurrent detection signal that is asserted when the low-side current is greater than the overcurrent threshold value;
• at least based on the overcurrent detection signal and the pulse modulation signal, generating a control pulse that takes a first level during a period when the high-side transistor should be on and the low-side transistor should be off, and takes a second level during a period when the high-side transistor should be off and the low-side transistor should be on;
• and
• driving the high-side transistor and the low-side transistor in response to the control pulse, wherein
• the generating of the control pulse includes:
• outputting the pulse modulation signal as the control pulse when the overcurrent detection signal is negated;
• setting the control pulse to the second level when the overcurrent detection signal is asserted;
• setting the control pulse to the first level during the fixed on time when the pulse modulation signal is at the first level and while the overcurrent detection signal is negated;
• outputting the pulse modulation signal as the control pulse when the pulse modulation signal is at the second level and while the overcurrent detection signal is negated.