Switching regulator

• US 20070035281A1
• Filed: 07/19/2006
• Published: 02/15/2007
• Est. Priority Date: 08/11/2005
• Status: Active Grant

• Current Assignee: Renesas Electronics Corporation
• Original Assignee: Renesas Technology Corporation (Renesas Electronics Corporation)
• Inventors: Kokami, Yasuhiko, Kuroiwa, Hiroshi, Yamashita, Osamu
• Granted Patent: US 7,492,132 B2
• Time in Patent Office: Days
• US Class Current: 323/222
• CPC Class Codes: H02M 1/0022 the disturbance parameters being input voltage fluctuations
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

The present invention provides a switching regulator having good stability compatible with a good response and an enhanced protection function. A first capacitor is placed between an output end of an inductor to generate an output voltage and a ground potential. From input voltage, a current is supplied to the inductor'"'"'s input end by a first switch element. A first feedback path includes a hysteretic comparator. An output voltage added to a voltage proportional to the current flowing through the inductor is supplied to the hysteretic comparator which discriminates whether the voltage is appropriate by hysteresis characteristics and generates a PWM control signal in accordance with an output current variation. Moreover, a second feedback path is provided to feed back an error amplifier output voltage with greater gain in a low frequency domain and an attenuation loop around a PWM frequency band to the comparator'"'"'s reference voltage input terminal. Feedback voltage through the second feedback path is used as a monitoring voltage in a protection circuit.

Claims

1. A switching regulator comprising:

an inductor;

a first capacitor placed between an output end of the inductor to generate an output voltage and a ground potential;

a first switch element which supplies a current from an input voltage to an input end of the inductor;

a second switch element which is turned on when the first switch element is turned off and energizes the input end of the inductor to a predetermined potential; and

a control circuit which generates a PWM control signal which is supplied to the first switch element so that the output voltage matches a desired voltage;

wherein the control circuit comprises;

a first feedback path and a second feedback path,

wherein the first feedback path includes;

a hysteretic comparator circuit; and

a series circuit comprising a first resistor and a second capacitor placed in parallel to the inductor,

wherein the comparator circuit receives a first reference voltage and a potential at a connection point of the first resistor and the second capacitor, discriminates whether the potential is appropriate by a first threshold and a second threshold, and generates the PWM control signal which varies the current flowing through the inductor in accordance with an output current variation,

wherein the second feedback path includes;

a third resistor and a fourth resistor to generate a fractional voltage of the output voltage; and

an error amplifier which receives the fractional voltage and a second reference voltage,

wherein the error amplifier generates the first reference voltage to be input to the comparator circuit, and

wherein the error amplifier is of a PI control type.

2. The switching regulator according to claim 1,

wherein the first switch element comprises a single power MOSFET,

wherein the first resistor and the second capacitor in the first feedback path comprise external elements,

wherein the third resistor and the fourth resistor in the second feedback path comprise external elements, and

wherein the comparator circuit and the error amplifier are formed in a semiconductor integrated circuit.

3. The switching regulator according to claim 2,

wherein the semiconductor integrated circuit includes a first terminal to control the first switch element, a second terminal for the first feedback path, and a third terminal for the second feedback path, and

wherein at least the second terminal is placed between the first terminal and the third terminal.

4. The switching regulator according to claim 3,

wherein a switch MOSFET is placed between an output terminal of the error amplifier and an input terminal to which the first reference voltage is input of the comparator circuit, formed in the semiconductor integrated circuit,

wherein the first feedback path includes a second resistor placed between the connection point of the first resistor and the second capacitor and a ground potential of the circuit, and

wherein a gate of the MOSFET is controlled by a control voltage generated by a time constant circuit which receives a power supply activation signal.

5. The switching regulator according to claim 4,

wherein the error amplifier includes:

a first amplifier of a current amplification type;

a third capacitor placed between an output terminal of the first amplifier and a ground potential of the circuit; and

a series circuit comprising a fifth resistor and a fourth capacitor placed between the output terminal of the first amplifier and the ground potential of the circuit.

13. The switching regulator according to claim 5,

wherein the third capacitor in the second feedback path is set to attenuate a PWM frequency component of the PWM control signal and a cutoff frequency of the fifth resistor and the fourth capacitor is set below a closed loop band in the first feedback path.

14. The switching regulator according to claim 13,

wherein the input voltage is 5 V or above, and

wherein the output voltage is 3.3 V or below.

6. A switching regulator comprising:

an inductor;

a first capacitor placed between an output end of the inductor to generate an output voltage and a ground potential;

a first switch element which supplies a current from an input voltage to an input end of the inductor;

a second switch element which is turned on when the first switch element is turned off and energizes the input end of the inductor to a predetermined potential; and

a control circuit which generates a PWM control signal which is supplied to the first switch element so that the output voltage matches a desired voltage;

wherein the control circuit comprises;

a first feedback path, a second feedback path, and a protection circuit,

wherein the first feedback path includes;

a hysteretic comparator circuit;

a series circuit comprising a first resistor and a second capacitor placed in parallel to the inductor; and

a second resistor placed between a connection point of the first resistor and the second capacitor and a ground potential of the circuit,

wherein the comparator circuit receives a first reference voltage and a feedback voltage from a connection point of the first resistor, the second resistor, and the second capacitor, discriminates whether the feedback voltage is appropriate by a first threshold and a second threshold, and generates the PWM control signal which varies the current flowing through the inductor in accordance with an output current variation,

wherein the second feedback path includes;

a third resistor and a fourth resistor to generate a fractional voltage of the output voltage; and

an error amplifier which receives the fractional voltage and a second reference voltage,

wherein the error amplifier generates the first reference voltage to be input to the comparator circuit,

wherein the protection circuit includes;

a level shift means to level shift the fractional voltage only by a first voltage; and

a first voltage comparator circuit which receives the level shifted fractional voltage and the first reference voltage,

wherein the level shifted voltage is set higher than the first reference voltage during normal operation of the switching regulator and set lower than the first reference voltage when a load short-circuit occurs with the first capacitor, and

wherein the first switch element is turned off by an output signal of the first voltage comparator circuit during the load short circuit.

7. The switching regulator according to claim 6,

wherein the protection circuit further comprises:

a second voltage comparator circuit which receives a third reference voltage corresponding to a maximum allowable voltage of the fractional voltage and the output voltage,

wherein the first switch element is turned off by an output signal of the second voltage comparator circuit when the output voltage has exceeded the maximum allowable voltage.

8. The switching regulator according to claim 7

wherein the protection circuit further comprises:

a third voltage comparator circuit which receives a feedback voltage from the comparator circuit and a fourth reference voltage; and

a first latch circuit which holds an output signal of the third voltage comparator circuit,

wherein the fourth reference voltage is set greater than the feedback voltage during the normal operation, a signal change when the feedback voltage has exceeded the fourth reference voltage is latched by the first latch circuit, and the first switch element is turned off by an output signal of the first latch circuit.

9. The switching regulator according to claim 8,

wherein a switch MOSFET is placed between the output terminal of the error amplifier and an input terminal to which the first reference voltage is input of the comparator circuit,

wherein the first feedback path includes a second resistor placed between the connection point of the first resistor and the second capacitor and a ground potential of the circuit, and

wherein a gate of the MOSFET is controlled by a control voltage generated by a time constant circuit which receives a power supply activation signal.

10. The switching regulator according to claim 9,

wherein the protection circuit further comprises:

a fourth voltage comparator circuit which receives the fractional voltage and a fifth reference voltage, a logic circuit which receives an output signal of the fourth voltage comparator circuit and its delayed signal, and a second latch circuit which holds an output signal of the logic circuit,

wherein the fifth reference voltage is set greater than the fractional voltage during the normal operation, a pulse rising at a time delayed by a delay circuit behind a signal change when the fractional voltage has dropped below the fifth reference voltage is latched by the second latch circuit, and the supply of the power supply activation signal is stopped by an output signal of the second latch circuit.

11. The switching regulator according to claim 10,

wherein the output signals of the first voltage comparator circuit, the second voltage comparator circuit, and the first lath circuit pass through a logical sum (OR) circuit and are delivered to turn the first switch element off and stop the supply of the power supply activation signal.

12. The switching regulator according to claim 11,

wherein the protection circuit further comprises:

a fifth voltage comparator circuit which receives the input voltage and a sixth reference voltage,

wherein the sixth reference voltage is set at a minimum allowable voltage of the input voltage, a signal change when the input voltage has dropped below the sixth reference voltage is delivered to the delay circuit and the logic circuit, and a pulse rising at a time thus delayed is latched by the second latch circuit and further delivered to stop the supply of the power supply activation signal.

15. The switching regulator according to claim 6,

wherein the error amplifier is a PI control type.

16. The switching regulator according to claim 15,

wherein the error amplifier includes:

a first amplifier of a current amplification type;

a third capacitor placed between the output terminal of the first amplifier and a ground potential of the circuit; and

a series circuit comprising a fifth resistor and a fourth capacitor placed between the output terminal of the first amplifier and the ground potential of the circuit;

17. The switching regulator according to claim 16,

wherein the third capacitor in the second feedback path is set to attenuate the PWM frequency component of the PWM control signal and the cutoff frequency of the fifth resistor and the fourth capacitor is set below the closed loop band in the first feedback path.

18. The switching regulator according to claim 17,

wherein the input voltage is 5 V or above, and

wherein the output voltage is 3.3 V or below.