Semiconductor device
There was a problem that it was difficult for a semiconductor device in the related art to increase the switching frequency of a step-up circuit, and it was difficult to stabilize an output current and an output voltage. A semiconductor device controls a step-up circuit including an inductor and a drive transistor to drive the inductor. The semiconductor device calculates upper and lower limits which determine the variable range of an input current, based on an output current and an input voltage, controls the switch timing of the drive transistor based on the relation between the upper and lower limits and the magnitude of the input current, and at the same time, corrects the upper and lower limits to be calculated, based on the magnitude of the difference between the output current and a target output current value as an ideal value of the output current.
1. A semiconductor device comprising:
a transistor disposed between a first node and a second node, the second node coupled to a first voltage;
an inductor that has first and second terminals, the first terminal coupled to the first node and the second terminal configured to receive a second voltage;
a drive circuit that outputs a control signal to a gate of the transistor based on a current value supplied to the inductor;
a resistor coupled to the second terminal of the inductor; and
a comparator that compares the voltage of the resistor with a predetermined value,
wherein the drive circuit detects the current value supplied to the inductor based on a result of the comparator,
wherein the drive circuit outputs the control signal to set the transistor in an ON-state during a period after the current value supplied to the inductor becomes less than a minimum current value until the current value supplied to the inductor exceeds a peak current value, and
wherein the drive circuit outputs the control signal to set the transistor in an OFF-state during a period after the current value supplied to the inductor exceeds the peak current value until the current value supplied to the inductor becomes less than the minimum current value.
2. The semiconductor device according to claim 1 , wherein the comparator includes first and second comparators,
wherein the first comparator compares the voltage of the resistor with a first predetermined value which is determined based on the peak current value,
wherein the second comparator compares the voltage of the resistor with a second predetermined value which is determined based on the minimum current value.
3. The semiconductor device according to claim 1 , wherein the drive circuit outputs a pulse width modulation (PWM) signal as the control signal.
4. The semiconductor device according to claim 1 , further comprising:
first and second output terminals; and
a capacitor disposed between the first and second output terminals.
5. The semiconductor device according to claim 4 , further comprising:
a diode disposed between the first node and the first output terminal.
6. A light emitting diode (LED) drive device, comprising:
a semiconductor device according to claim 4 ,
wherein the first and second output terminals are configured to couple to at least one LED.
7. The semiconductor device according to claim 1 , wherein the transistor is an NMOS transistor.