Thermal shutdown unit, switch controller including the same, and control method of thermal shutdown protection operation

A thermal shutdown unit controlling a thermal shutdown protection operation of a controller controlling an operation of an SMPS, comprising;

• at least one diode;
• a shutdown comparator comparing a temperature sensing voltage generated in the at least one diode with a thermal shutdown reference voltage to control the thermal shutdown protection operation;
• and
• a thermal shutdown reference voltage selection circuit outputting the thermal shutdown reference voltage and varying the thermal shutdown reference voltage according to an operation state of the SMPS,
• wherein the temperature sensing voltage is varied according to heat generated in the controller, the operation state of the SMPS includes an overload state and a start-up state, the thermal shutdown reference voltage selection circuit sets the thermal shutdown reference voltage to a third thermal shutdown reference voltage when the SMPS is in the overload state and to a second thermal shutdown reference voltage when the SMPS is in the start-up state, and the third thermal shutdown reference voltage indicates a temperature that is lower than a temperature indicated by the second thermal shutdown reference voltage.

A switch controller controlling a switching operation of a power switch controlling an operation of an SMPS, comprising:

• a PWM controller controlling turn-off of a power switch according to a feedback voltage corresponding to an output voltage and a sensing voltage corresponding to a current flowing through the power switch, and turning on the power switch according to a clock signal determining a switching frequency of the power switch;
• and
• a thermal shutdown unit varying a thermal shutdown reference voltage controlling a thermal shutdown protection operation of the switch controller according to an operation state of the SMPS, and generating a thermal shutdown signal and transmitting it the thermal shutdown signal to the PWM controller if a temperature sensing voltage corresponding to a temperature of the switch controller reaches the thermal shutdown reference voltage,
• wherein the PWM controller turns off the power switch according to the thermal shutdown signal, and the thermal shutdown unit sets the thermal shutdown reference voltage to a third thermal shutdown reference voltage when the SMPS is in an overload state and to a second thermal shutdown reference voltage when the SMPS is in a start-up state, and the third thermal shutdown reference voltage indicates a temperature that is lower than a temperature indicated by the second thermal shutdown reference voltage.