METHOD AND APPARATUS FOR EXTERNAL CONTROL MODE STEP DOWN SWITCHING REGULATOR

• US 20090153127A1
• Filed: 12/12/2007
• Published: 06/18/2009
• Est. Priority Date: 12/12/2007
• Status: Active Grant

• Current Assignee: Monolithic Power Systems Incorporated
• Original Assignee: Monolithic Power Systems Incorporated
• Inventors: Chen, Wei
• Granted Patent: US 7,679,341 B2
• Time in Patent Office: Days
• US Class Current: 323/350
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A switching regulator integrated circuit (IC) is disclosed that includes a switch circuit that further includes a first switch and a second switch, a mode selector circuit controlled by external circuitry to select between a first mode and a second mode, and a control circuit. In response to a feedback signal from the switch circuit, when the first mode is selected, the control circuit toggles the first switch and the second switch ON and OFF alternately at a fixed first frequency. When a second mode is selected, the control circuit causes the second switch to turn OFF completely and the first switch to switch ON and OFF at a variable second frequency.

Claims

1. A switching regulator integrated circuit, comprising:

a switch circuit including a first switch and a second switch;

a mode selector circuit controlled by external circuitry to select between a first mode and a second mode; and

a control circuit electrically coupled to said mode selector circuit and to said switch circuit, wherein, in response to a feedback signal from said switch circuit, when said first mode is selected, said control circuit is operable to cause said first switch and said second switch to switch ON and OFF alternately at a fixed first frequency, when a second mode is selected, said control circuit is operable to cause said second switch to turned OFF completely and said first switch to switch ON and OFF at a variable second frequency.

2. The switching regulator integrated circuit of claim 1 wherein during said second mode said first switch switches ON and OFF at said variable second frequency until said variable second frequency approaches substantially to said fixed first frequency.

3. The switching regulator integrated circuit of claim 1 wherein said switch circuit is electrically coupled to an output circuit that further comprises:

an inductor; and

an output capacitor electrically coupled to said inductor, wherein said output circuit is operable to generate a regulated output voltage at an output node of said output circuit.

4. The switching regulator integrated circuit of claim 2 wherein said switch circuit further comprises a Schottky diode, said first switch and said Schottky diode conduct alternately in said second mode so as to provide an output current that charges and maintains said output capacitor at said regulated output voltage.

5. The switching regulator integrated circuit of claim 3 wherein during said second mode, said control circuit is operable to turn on said first switch for a fixed period of time, and then turn off said first switch completely until said regulated voltage at said output node decreases substantially to a reference voltage at which time said first switch is turned on again for said fixed period of time, whereby said first switch is toggled at said variable second frequency.

6. The switching regulator integrated circuit of claim 1 wherein said external circuitry comprises a microprocessor.

7. The switching regulator integrated circuit of claim 1 wherein said external circuitry comprises an Application Specific Integrated Circuit (ASIC).

8. The switching regulator integrated circuit of claim 1 wherein said external circuitry further comprises a storage device.

9. The switching regulator integrated circuit of claim 1 wherein said mode selector circuit, upon receiving an instruction from said external circuitry, operable to cause said control circuit to change between said first mode and said second mode.

10. The switching regulator integrated circuit of claim 8 wherein said mode selector circuit further comprises:

a frequency comparator circuit, electrically coupled to said switch circuit and said control circuit, operable to compare said first fixed frequency and said second variable frequency so as to issue a logic signal; and

a logic circuitry, electrically coupled to receive said logic signal of said frequency comparator circuit, operable to drive said control circuit and said switch circuit.

11. The switching regulator integrated circuit of claim 1 wherein said control circuit further comprises:

a pulse width modulation (PWM) controller electrically coupled to said mode control circuit, operable to drive said switch circuit in response to said mode control signal;

an oscillator circuit electrically coupled to provide said first frequency to said PWM controller; and

a plurality of comparator circuits, electrically coupled to receive said feedback signal from the output of said switch circuit, operable to drive said PWM controller.

12. The switching regulator integrated circuit of claim 1 further comprises a bootstrap circuit that comprises:

a Schottky diode electrically coupled to said control circuit; and

a boot strap capacitor electrically coupled to the cathode of said Schottky diode and to said output node of said switch circuit.

13. A method of providing an efficient and low noise control for a switching regulator integrated circuit (IC) having a mode selector circuit, a control circuit, and a switch circuit further including a high side switch and a low side switch, the method comprising the steps of:

selecting either a first mode or a second mode upon receiving an instruction from an external circuitry;

switching on and off said switching regulator alternately at a constant first frequency so as to provide a DC output voltage when said first mode is selected; and

whenever said second mode is selected, switching on and off said high side switch at a variable second frequency so as to continue providing an output current that charges and maintains an output capacitor at said DC output voltage while turning off said low side power switch completely.

14. The method of claim 13 wherein said turning off and on said high side power switch at said a variable second frequency further comprising:

turning on said high side switch for a fixed period of time; and

turning off said high side switch until said desired output voltage level drops to a reference voltage.

15. The method of claim 14 further wherein said switching on and off said high-side switch at said variable second frequency during said second mode further comprising:

monitoring said variable second frequency;

whenever said variable second frequency approaches substantially to said constant first frequency, terminating said second mode and returning to said first mode.

16. The method of claim 13 wherein said switching on and off said switching regulator alternately at said constant first frequency further comprises substantially reducing a conduction loss during a dead time.

17. The method of claim 13 further comprises:

conducting current during dead time in said first mode; and

conducting current during the off state of said high-side switch in said second mode.

18. A power supply system for a portable device, comprising:

(1) a single battery source for providing an unregulated DC input voltage;

(2) a microprocessor; and

(3) a switching regulator integrated circuit electrically coupled to receive said unregulated DC input voltage from said single battery source and to provide a regulated output voltage to said microprocessor, said switching regulator integrated circuit further comprising;

(a) a switch circuit including a first switch and a second switch;

a mode selector circuit controlled by external circuitry to select between a first mode and a second mode; and

(b) a control circuit electrically coupled to said mode selector circuit and to said switch circuit, wherein, in response to a feedback signal from said switch circuit, when said first mode is selected, said control circuit is operable to cause said first switch and said second switch to switch ON and OFF alternately at a fixed first frequency, when a second mode is selected, said control circuit is operable to cause said second switch to turned OFF completely and said first switch to switch ON and OFF at a variable second frequency

19. The power supply system of claim 18 wherein during said second mode said second switch switches until said variable second frequency approaches substantially to said fixed first frequency.

20. The power supply system of claim 18 wherein said switch circuit is electrically coupled to an output circuit that further comprises:

an inductor; and

an output capacitor electrically coupled in series to said inductor, wherein said output circuit is operable to generate a regulated output voltage at an output node of said output circuit.

21. The power supply system of claim 19 wherein said switch circuit further comprises a Schottky diode, said first switch and said Schottky diode conduct alternately so as to provide an output current that charges and maintains said output capacitor at said regulated output voltage.

22. The power supply system of claim 20 wherein during said second mode, said control circuit is operable to turn on said first switch for a fixed period of time, and then turn off said first switch completely until said regulated voltage at said output node decreases substantially to a reference voltage at which time said first switch is turned on again for said fixed period of time, whereby said first switch is toggled at said variable second frequency.