DCR inductor current-sensing in four-switch buck-boost converters

Patent metadata

Field	Value
Publication number	US-10084381-B2
Application number	US-201715654568-A
Country	US
Kind code	B2
Filing date	Jul 19, 2017
Priority date	Sep 24, 2014
Publication date	Sep 25, 2018
Grant date	Sep 25, 2018

Abstract

An inductor current-sensing circuit for measuring a current in an inductor includes (a) a first RC network coupled between a first terminal of the inductor and a reference voltage source; and (b) a second RC network coupled between a second terminal of the inductor and the reference voltage source. The first RC network and the second RC network each have a time constant substantially equal to the ratio between the inductance and the DC resistance of the inductor. The inductor which current is being measured may be a primary inductor of a four-switch buck boost converter receiving an input voltage and providing an output voltage.

First claim

We claim:

1. An inductor current-sensing circuit for measuring a current in an inductor having an inductance and an equivalent DC resistance, comprising:
a sensing resistor connected in series with the inductor;
a first RC network coupled between a first terminal of the sensing resistor and a reference voltage source, the reference voltage source providing a virtual ground reference;
a second RC network coupled between a second terminal of the sensing resistor and the virtual ground reference; and
a decoupling capacitor connecting the virtual ground reference to a system ground reference.

2. The inductor current-sensing circuit of claim 1 , wherein the first RC network and the second RC network each have a time constant substantially equal to a ratio between the inductance and the DC resistance.

3. The inductor current-sensing circuit of claim 1 , wherein the first RC network comprises:
a sensing capacitor having a first terminal and a second terminal, the second terminal being coupled to the reference voltage source;
a first resistor coupled between the first terminal of the sensing resistor and the first terminal of the sensing capacitor;
a blocking capacitor having a first terminal and a second terminal, the second terminal of the blocking capacitor being coupled to one terminal of the inductor; and
a second resistor coupled between the first terminal of the sensing capacitor and the first terminal of the blocking capacitor.

4. The inductor current-sensing circuit of claim 3 , wherein the second RC network comprises:
a sensing capacitor having a first terminal and a second terminal, the second terminal being coupled to the reference voltage source;
a first resistor coupled between the second terminal of the sensing resistor and the first terminal of the sensing capacitor of the second RC network;
a blocking capacitor having a first terminal and a second terminal, the second terminal of the blocking capacitor of the second RC network being coupled to one terminal of the inductor; and
a second resistor coupled between the first terminal of the sensing capacitor of the second RC network and the first terminal of the blocking capacitor of the second RC network.

5. The inductor current-sensing circuit of claim 4 , wherein a ratio in resistance value between the second resistor of the second RC network and the first resistor of the second resistor network less one is substantially a ratio in resistance value between the sensing resistor and the equivalent DC resistance of the inductor.

6. The inductor current-sensing circuit of claim 4 , wherein the blocking capacitor in each of the first and the second RC networks has a capacitance that is greater than a capacitance of the sensing capacitor in the corresponding one of the first and second RC networks.

7. The inductor current-sensing circuit of claim 1 , wherein the inductor is a primary inductor of a four-switch buck boost converter receiving an input voltage and providing an output voltage.

8. The inductor current-sensing circuit of claim 7 , wherein the virtual ground reference refers to the output voltage when the four-switch buck boost converter operates in a buck mode.

9. The inductor current-sensing circuit of claim 7 , wherein the virtual ground reference refers to the input voltage when the four-switch buck boost converter operates in a boost mode.

10. The inductor current-sensing circuit of claim 7 , wherein the virtual ground reference refers to an average of a voltage across a first terminal of the sensing resistor and one terminal of the inductor, when the four-switch buck boost converter operates in a buck-boost mode.

11. The inductor current-sensing circuit of claim 1 , further comprising an additional sensing capacitor connected between the first RC network and the second RC network.

12. The inductor current-sensing circuit of claim 11 , wherein the additional sensing capacitor has a greater capacitance than a capacitance of the sensing capacitor in each of the first and the second RC networks.

13. A method for measuring a current in an inductor having an inductance and an equivalent DC resistance, comprising:
connecting a sensing resistor in series with the inductor;
coupling a first RC network between a first terminal of the sensing resistor and a reference voltage source, the reference voltage source providing a virtual ground reference;
coupling a second RC network between a second terminal of the sensing resistor and the virtual voltage reference;
measuring a voltage between a node in the first RC network and a node in the second RC network; and
connecting a decoupling capacitor between the virtual ground reference and a system ground reference.

14. The method of claim 13 , wherein the first RC network and the second RC network each have a time constant substantially equal to a ratio between the inductance and the DC resistance.

15. The method of claim 13 , wherein the first RC network comprises:
a sensing capacitor having a first terminal and a second terminal, the second terminal being coupled to the reference voltage source;
a first resistor coupled between the first terminal of the sensing resistor and the first terminal of the sensing capacitor;
a blocking capacitor having a first terminal and a second terminal, the second terminal of the blocking capacitor being coupled to one terminal of the inductor; and
a second resistor coupled between the first terminal of the sensing capacitor and the first terminal of the blocking capacitor.

16. The method of claim 13 , wherein the second RC network comprises:
a sensing capacitor having a first terminal and a second terminal, the second terminal being coupled to the reference voltage source;
a first resistor coupled between the second terminal of the sensing resistor and the first terminal of the sensing capacitor of the second RC network;
a blocking capacitor having a first terminal and a second terminal, the second terminal of the blocking capacitor of the second RC network being coupled to one terminal of the inductor; and
a second resistor coupled between the first terminal of the sensing capacitor of the second RC network and the first terminal of the blocking capacitor of the second RC network.

17. The method of claim 16 , wherein measuring the voltage comprises measuring across the first terminal of the sensing capacitor in the first RC network and the first terminal of the sensing capacitor in the second RC network.

18. The method of claim 16 , wherein ratio in resistance value between the second resistor of the second RC network and the first resistor of the second resistor network less one is substantially a ratio in resistance value between the sensing resistor and the equivalent DC resistance of the inductor.

19. The method of claim 16 , wherein the blocking capacitor in each of the first and the second RC networks has a capacitance that is greater than a capacitance of the sensing capacitor in the corresponding one of the first and the second RC networks.

20. The method of claim 13 , wherein the inductor is a primary inductor of a four-switch buck boost converter receiving an input voltage and providing an output voltage.

21. The method of claim 20 , wherein the virtual ground reference refers to the output voltage when the four-switch buck boost converter operates in a buck mode.

22. The method of claim 20 , wherein the virtual ground reference refers to the input voltage when the four-switch buck boost converter operate

Assignees

• Linear Tech Corp
• Linear Tech Llc

Inventors

• Zhang Xu
• Li Jian
• Shi Zhouyuan
• Gu Yi Ding

Classifications

• H02M2001/0009

  Electricity · mapped topic

• H02M3/1582 Primary

  Buck-boost converters (H02M3/1584 takes precedence) · CPC title

• H02M1/0009

  Devices or circuits for detecting current in a converter · CPC title