Switching regulator

• US 7,492,132 B2
• Filed: 07/19/2006
• Issued: 02/17/2009
• Est. Priority Date: 08/11/2005
• Status: Expired due to Fees

• Current Assignee: Renesas Electronics Corporation
• Original Assignee: Renesas Technology Corporation (Renesas Electronics Corporation)
• Inventors: Kokami, Yasuhiko, Kuroiwa, Hiroshi, Yamashita, Osamu
• Primary Examiner(s): Ullah; Akm E
• Assistant Examiner(s): Zhang; Jue
• Application Number:
  US11/488,833
• Publication Number:
  US 20070035281A1
• Time in Patent Office: 944 Days
• Field of Search: 323/222, 323/282, 323/285, 323/288, 323/224, 323/283
• 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 arranged between an output end of the inductor to generate an output voltage and a ground potential;

a first switch element to supply 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 supplied to the first switch element so that the output voltage matches a desired voltage, the control circuit having a first feedback path and a second feedback path,

wherein the first feedback path includes;

a hysteretic comparator circuit; and

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

wherein the hysteretic comparator circuit receives a first reference voltage and a potential at a connection point of the first resistor and the second capacitor, determines whether the potential satisfies a first threshold and a second threshold, and generates the PWM control signal to vary 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 circuit which receives the fractional voltage and a second reference voltage,

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

wherein the error amplifier circuit is a PI control error amplifier circuit,

wherein the first switch element includes a single power MOSFET,

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

wherein the first resistor and the second capacitor of the series circuit are external to the semiconductor integrated circuit,

wherein the third resistor and the fourth resistor of the second feedback path are external to the semiconductor integrated circuit,

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

wherein at least the second terminal is arranged between the first terminal and the third terminal,

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

wherein the first feedback path includes a second resistor arranged 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 switch MOSFET is controlled by a control voltage generated by a time constant circuit which receives a power supply activation signal.

2. The switching regulator according to claim 1,

wherein the error amplifier circuit includes:

a first current amplifier;

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

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

3. The switching regulator according to claim 2,

wherein the third capacitor of the error amplifier circuit is set to attenuate a PWM frequency component of the PWM control signal, and

wherein a cutoff frequency of the fifth resistor and the fourth capacitor is set below a closed loop band of the first feedback path.

4. The switching regulator according to claim 3,

wherein the input voltage is 5 V or above, and

wherein the output voltage is 3.3 V or below.