Methods and apparatus for a spread spectrum switching regulator
View Patent ↗A spread spectrum switching regulator generally includes an reactive circuit portion coupled to the input terminal, a switching element coupled to the reactive circuit portion, and a control circuit portion coupled between the switching element and the output terminal. The switching element has a drive signal characterized by a duty cycle, and the reactive circuitry portion is configured to produce an output voltage at the output terminal responsive to the duty cycle of the drive signal. The control circuit portion is configured to spread the input power across multiple frequencies by adjusting the drive signal of the switching element, thereby reducing input current noise through spread spectrum techniques. The drive signal is responsive to a pseudo-randomly generated ramp signal.
1. A spread spectrum switching regulator having an input terminal and an output terminal, the switching regulator comprising:
a reactive circuit portion coupled to the input terminal;
a switching element coupled to the reactive circuit portion, the switching element configured to accept a drive signal having a duty cycle and to effect switching of the reactive circuit portion to produce an output voltage at the output terminal responsive to the duty cycle; and
a control circuit portion coupled between the switching element and the output terminal, the control circuit portion configured to adjust the drive signal in accordance with a ramp signal; and
a ramp generator coupled to the control circuit portion, wherein the ramp generator is configured to produce the ramp signal with a ramp slope and a frequency that is pseudo-randomly selected.
2. The switching regulator of claim 1 , wherein the switching regulator is configured to operate in a continuous mode (CCM), and wherein the ramp slope and frequency are selected such that the duty cycle of the switching element remains substantially constant.
3. The switching regulator of claim 1 , wherein the control circuit includes an oscillator configured to produce the selectable frequency, and the ramp generator configured to produce the selectable ramp slope.
4. The regulator of claim 1 , wherein the control circuit portion further includes a comparator configured to compare the ramp signal and an error signal to produce the drive signal.
5. The regulator of claim 4 , wherein the control circuit portion further includes an operational amplifier configured to compare the output voltage with a reference voltage to produce the error signal.
6. The regulator of claim 1 , wherein the reactive circuit portion is configured such that the output voltage is less than the input voltage.
7. The regulator of claim 1 , wherein the reactive circuit portion is configured such that the output voltage is greater than the input voltage.
8. The regulator of claim 7 , wherein the reactive circuit portion includes:
an inductive element coupled between the input terminal and a first node, wherein the first node is coupled to the switching element;
a diode element coupled between the first node and the output terminal; and
a capacitive element coupled between the output voltage and a ground node.
9. A spread spectrum switching regulator having an input terminal and an output terminal, the switching regulator comprising:
a reactive circuit portion coupled to the input terminal;
a switching element coupled to the reactive circuit portion, the switching element configured to accept a drive signal having a duty cycle and to effect switching of the reactive circuit portion to produce an output voltage at the output terminal responsive to the duty cycle; and
a control circuit portion coupled between the switching element and the output terminal, the control circuit portion configured to produce a ramp signal having a selectable frequency and a selectable ramp slope, and to adjust the drive signal in accordance with the ramp signal, wherein the control circuit portion further includes a pseudo-random number generator configured to pseudo-randomly select the frequency.
10. The switching regulator of claim 9 , wherein the reactive circuit portion is characterized by an input power, and wherein the control circuit portion is configured to select the frequency and the ramp slope such that the input power is spread across multiple frequencies.
11. A spread spectrum switching regulator having an input terminal and an output terminal, the switching regulator comprising:
a reactive circuit portion coupled to the input terminal;
a switching element coupled to the reactive circuit portion, the switching element configured to accept a drive signal having a duty cycle and to effect switching of the reactive circuit portion to produce an output voltage at the output terminal responsive to the duty cycle; and
a control circuit portion coupled between the switching element and the output terminal, the control circuit portion configured to produce a ramp signal having a selectable frequency and a selectable ramp slope, and to adjust the drive signal in accordance with the ramp signal, wherein the switching regulator is configured to operate in a discontinuous mode (DCM), and wherein the ramp slope and the frequency are selected such that the ramp slope remains substantially proportional to the square root of the frequency.
12. A method for reducing noise in a switching regulator of the type having an input terminal, an output terminal, and an reactive circuit portion coupled to the input terminal, wherein the reactive circuit portion has an input voltage and an input power, the method comprising:
providing a switching element coupled to the reactive circuit portion, the switching element configured to accept a drive signal having a duty cycle;
providing a control circuit portion between the switching element and the output terminal;
generating a ramp signal having a pseudo-randomly selected frequency and a ramp slope; and
generating the drive signal by comparing the ramp signal to an error signal, wherein the error signal is based on the difference between the output voltage and a reference voltage.
13. The method of claim 12 , wherein, during step of generating the ramp signal, the ramp slope remains substantially proportional to the square root of the ramp frequency.
14. The method of claim 12 , wherein generating the ramp signal includes modulating the ramp slope pseudo-randomly.
15. A method for reducing noise in a switching regulator of the type having an input terminal, an output terminal, and an reactive circuit portion coupled to the input terminal, wherein the reactive circuit portion has an input voltage and an input power, the method comprising:
providing a switching element coupled to the reactive circuit portion, the switching element configured to accept a drive signal having a duty cycle;
providing a control circuit portion between the switching element and the output terminal;
generating a ramp signal having a frequency and a ramp slope, wherein generating the ramp signal includes generating a pseudo-random ramp frequency; and
generating the drive signal by comparing the ramp signal to an error signal, wherein the error signal is based on the difference between the output voltage and a reference voltage.
16. The method of claim 15 , wherein the duty cycle of the switching element remains substantially constant during the step of generating the drive signal.
17. A spread spectrum boost regulator comprising:
an input terminal;
an output terminal;
an reactive circuit portion coupled to the input terminal, the reactive circuit portion including an inductive element coupled between the input terminal and a first node, a diode element coupled between the first node and the output terminal, and a capacitive element coupled between the output voltage and a ground node;
a switching element coupled to the first node, the switching element responsive to a drive signal having a duty cycle, wherein the reactive circuitry portion is configured to produce, in response to the duty cycle of the drive signal; the output voltage;
a control circuit portion coupled between the switching element and the output terminal, the control circuit including an oscillator coupled to a ramp generator, wherein the oscillator is configured to produce an oscillator signal having an oscillator frequency, and the ramp generator is configured to produce a ramp signal having a ramp slope at the oscillator frequency, and wherein the ramp slope and the oscillator frequency may be pseudo-randomly selected to adjust the drive signal.
18. The regulator of claim 17 , wherein the control circuit portion further includes a comparator configured to compare the ramp signal and an error signal to produce the drive signal.
19. The regulator of claim 18 , wherein the control circuit portion further includes an operational amplifier configured to compare the output voltage with a reference voltage to produce the error signal.
20. The switching regulator of claim 19 , wherein the ramp slope is selected such that it remains substantially proportional to the square root of the oscillator frequency.