LOW-TO-MEDIUM POWER SINGLE CHIP DIGITAL CONTROLLED DC-DC REGULATOR FOR POINT-OF-LOAD APPLICATIONS

• US 20120153917A1
• Filed: 12/20/2011
• Published: 06/21/2012
• Est. Priority Date: 12/20/2010
• Status: Active Grant

• Current Assignee: Arizona State University, Ira A. Fulton Schools Of Engineering, California Institute of Technology
• Original Assignee: Arizona State University, Ira A. Fulton Schools Of Engineering, California Institute of Technology
• Inventors: Bakkaloglu, Bertan, Adell, Philippe C., Vermeire, Bert, Liu, Tao
• Granted Patent: US 9,024,606 B2
• Time in Patent Office: Days
• US Class Current: 323/283
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/0012 Control circuits using digital or numerical techniques in DC/DC converters H02M3/157, H02M3/33515; in DC-AC converters H02M7/53873
• 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 DC-DC converter for generating a DC output voltage includes: a digitally controlled pulse width modulator (DPWM) for controlling a switching power stage to supply a varying voltage to an inductor; and a digital voltage feedback circuit for controlling the DPWM in accordance with a feedback voltage corresponding to the DC output voltage, the digital voltage feedback circuit including: a first voltage controlled oscillator for converting the feedback voltage into a first frequency signal and to supply the first frequency signal to a first frequency discriminator; a second voltage controlled oscillator for converting a reference voltage into a second frequency signal and to supply the second frequency signal to a second frequency discriminator; a digital comparator for comparing digital outputs of the first and second frequency discriminators and for outputting a digital feedback signal; and a controller for controlling the DPWM in accordance with the digital feedback signal.

Claims

1. A DC-DC converter configured to generate a DC output voltage, the DC-DC converter comprising:

a digitally controlled pulse width modulator configured to control a switching power stage to supply a varying voltage to an inductor; and

a digital voltage feedback circuit configured to control the digitally controlled pulse width modulator in accordance with a feedback voltage corresponding to the DC output voltage, the digital voltage feedback circuit comprising;

a first voltage controlled oscillator configured to convert the feedback voltage into a first frequency signal and to supply the first frequency signal to a first frequency discriminator;

a second voltage controlled oscillator configured to convert a reference voltage into a second frequency signal and to supply the second frequency signal to a second frequency discriminator;

a digital comparator configured to compare digital outputs of the first and second frequency discriminators and to output a digital feedback signal; and

a controller configured to control the digitally controlled pulse width modulator in accordance with the digital feedback signal.

2. The DC-DC converter of claim 1, further comprising:

a triangular current source coupled to the inductor; and

a read-out circuit for measuring a voltage across the inductor, the read-out circuit comprising;

a low-pass filter having a first terminal coupled to a first end of the inductor and a second terminal coupled to a second end of the inductor, the low-pass filter supplying an inductor voltage corresponding to the voltage across the inductor; and

a third voltage controlled oscillator configured to convert the inductor voltage into a third frequency signal and to supply the third frequency signal to a third frequency discriminator, the third frequency discriminator being coupled to the digital comparator to compare the digital outputs of the second and third frequency discriminators;

wherein the controller is configured to measure an inductance of the inductor based on a magnitude of a voltage waveform of the inductor voltage, the voltage waveform being generated when a triangular current waveform is applied to the inductor, and

wherein the controller is further configured to control the digitally controlled pulse width modulator in accordance with the measured inductance.

3. The DC-DC converter of claim 2, wherein the controller is further configured to measure a resistance of the inductor based on a slope of the voltage waveform of the inductor voltage.

4. The DC-DC converter of claim 3, wherein the controller is further configured to compute a magnitude of a current flowing through a load coupled to the DC output voltage, the magnitude of the current being computed in accordance with the voltage across the inductor and the measured resistance of the inductor.

5. The DC-DC converter of claim 2, wherein the low-pass filter is a first order low pass filter.

6. The DC-DC converter of claim 5, wherein the low-pass filter comprises:

an op-amp; and

a feedback resistor and a feedback capacitor coupled in parallel between the output of the op-amp and an inverting input of the op-amp.

7. The DC-DC converter of claim 6, further comprising a DC-offset control circuit, the DC-offset control circuit comprising:

a feedback resistor and a feedback capacitor coupled in parallel between a reference voltage source and a non-inverting input of the op-amp.

8. The DC-DC converter of claim 2, wherein the low-pass filter is a Sallen-Key or Tow-Thomas biquad filter.

9. The DC-DC converter of claim 1, wherein the DC-DC converter is a buck converter, a boost converter, or a buck-boost converter.

10. The DC-DC converter of claim 1, further comprising a CIC decimator coupled between the digital comparator and the controller and configured to decimate the digital feedback signal received from the digital comparator and to supply the decimated digital feedback signal to the controller.

11. The DC-DC converter of claim 1, further comprising a plurality of CIC decimators, each of the CIC decimators being coupled between a corresponding one of the frequency discriminators and the digital comparator and configured to decimate the digital outputs received from the frequency discriminators and to supply the decimated digital outputs to the digital comparator.

12. The DC-DC converter of claim 1, wherein the digitally controlled pulse width modulator is configured to have an output duty cycle controlled by a plurality of most significant bits and a plurality of least significant bits, and

wherein the digitally controlled pulse width modulator comprises:

a counter configured to supply the most significant bits; and

a delay locked loop configured to supply the least significant bits.

13. A method of operating a DC-DC converter comprising an inductor, the method comprising, during power up of the DC-DC converter:

supplying a triangular current to the inductor;

measuring a voltage waveform across the inductor;

computing an inductance of the inductor based on a magnitude of the voltage waveform;

computing a resistance of the inductor based on a slope of the voltage waveform; and

configuring a controller to apply driving waveforms to the inductor in accordance with the computed inductance and the computed resistance.

14. The method of claim 13, wherein the measuring the voltage waveform across the inductor comprises:

low-pass filtering an inductor voltage measured across the inductor;

converting the filtered inductor voltage to a first frequency signal corresponding to the inductor voltage;

converting the first frequency signal into a first digital signal corresponding to the frequency of the first frequency signal;

converting a first reference voltage to a second frequency signal corresponding to the first reference voltage;

converting the second frequency signal into a second digital signal corresponding to the frequency of the second frequency signal; and

comparing the first digital signal to the second digital signal to produce the measured voltage waveform across the inductor.

15. The method of claim 14, further comprising decimating the first digital signal and the second digital signal,

wherein the comparing the first digital signal to the second digital signal comprises comparing the decimated first digital signal and the decimated second digital signal.

16. The method of claim 14, further comprising decimating the measured voltage waveform.

17. The method of claim 13, further comprising, during operation of the DC-DC converter:

converting an output voltage of the DC-DC converter to a third frequency signal corresponding to the output voltage;

converting the third frequency signal to a third digital signal corresponding to the frequency of the third frequency signal;

converting a second reference voltage to a fourth frequency signal corresponding to the second reference voltage;

converting the fourth frequency signal into a fourth digital signal corresponding to the frequency of the fourth frequency signal; and

comparing the third digital signal to the fourth digital signal to produce a digital feedback signal.

18. The method of claim 13, further comprising, during operation of the DC-DC converter:

measuring a current sense voltage across the inductor; and

computing a load current flowing through a load coupled to an output of the DC-DC converter in accordance with the measured current sense voltage and the computed resistance.