Methods and apparatus for current sensing in mutually coupled inductors

1. A multiphase power supply for supplying a current to a load through multiple phases of inductors, comprising:

a control system adapted to control the current through the inductors according to one or more branch inductor current signals;

multiple current sensors connected to the control system, wherein each current sensor:

comprises a series combination comprising a capacitor and a resistor, wherein the series combination is adapted to be connected in parallel with one of the inductors; and

is adapted to generate one of the branch inductor current signals according to a sensed current in the connected inductor; and

a coupling capacitor coupled between at least two of the current sensors.

2. A multiphase power supply according to claim 1 , wherein the coupling capacitor is coupled to a node between the resistor and the capacitor for each current sensor to which the coupling capacitor is coupled.

3. A multiphase power supply according to claim 1 , wherein a capacitance of the coupling capacitor is selected according to a resistance of the resistor of the current sensors to which the coupling capacitor is attached, a DC resistance of the inductors to which the coupled current sensors are attached, and a mutual coupling inductance between at least two of the inductors to which the coupled current sensors are attached.

4. A multiphase power supply according to claim 1 , wherein each current sensor further comprises a second resistor comprising a first terminal connected to a first terminal of the capacitor and a second terminal connected to a second terminal of the capacitor, wherein:

the DC impedance of the first resistor, the second resistor, and the capacitor substantially match the DC impedance of the inductor with respect to the control system; and

the resistance of the first resistor and the resistance of the second resistor are selected according to a desired voltage range of the branch inductor current signal.

5. A multiphase power supply according to claim 4 , wherein the resistance of the first resistor and the resistance of the second resistor are further selected according to a self resistance of the inductor and an anticipated current range through the inductor.

6. A multiphase power supply according to claim 1 , further comprising an output stage responsive to the control system and adapted to:

connect to the inductors; and

supply the current through the inductors according to a signal from the control system.

7. A multiphase power supply according to claim 1 , wherein the control system comprises a PWM controller.

8. A current sense network for sensing a current in a first inductor mutually coupled to a second inductor, comprising:

an inductor branch, comprising:

an inductor exhibiting a series parasitic DC resistance (DCR) and comprising an input node and an output node, wherein:

the input node is coupled to a branch voltage signal; and

the output node generates an output voltage signal responsive to the branch voltage signal;

a resistive capacitive (RC) sense circuit comprising a resistor and a capacitor in a series combination, wherein:

the RC sense circuit is coupled to the input and output nodes of the inductor branch in parallel with the inductor; and

a voltage across the capacitor generates a sense voltage signal corresponding to the sensed current flowing through the inductor branch; and

a coupling circuit coupled to the RC sense circuit and comprising at least one capacitor, wherein a capacitance of the capacitor is selected according to an inductance between the mutually coupled first inductor and second inductor.

9. A current sense network according to claim 8 , wherein the coupling circuit is coupled to a node between the resistor and the capacitor of the sense circuit.

10. A current sense network according to claim 8 , wherein a capacitance of the coupling circuit capacitor is selected according to a resistance of the resistor of the sense circuit and a DC resistance of the first inductor.

11. A current sense network according to claim 8 , wherein the sense circuit further comprises a second resistor comprising a first terminal connected to a first terminal of the sense circuit capacitor and a second terminal connected to a second terminal of the sense circuit capacitor, wherein:

the DC impedance of the first resistor, the second resistor, and the capacitor substantially match the DC impedance of the inductor branch with respect to the control system; and

the resistance of the first resistor and the resistance of the second resistor are selected according to a desired voltage range of the branch inductor current signal.

12. A current sense network according to claim 11 , wherein the resistance of the first resistor and the resistance of the second resistor are further selected according to a self resistance of the first inductor and an anticipated current range through the first inductor.

13. A method of generating a signal corresponding to a current in a first inductor mutually coupled to a second inductor, comprising:

connecting a sense circuit comprising a series combination of a capacitor and a first resistor in parallel with the first inductor;

connecting a coupling circuit to the series combination, wherein the coupling circuit includes a coupling capacitor; and

selecting a capacitance of the coupling capacitor according to an inductance of the mutual coupling between the first inductor and the second inductor.

14. A method of generating a signal according to claim 13 , wherein connecting the coupling circuit comprises connecting the coupling circuit to a node between the first resistor and the sense circuit capacitor.

15. A method of generating a signal according to claim 13 , wherein a time constant of the first resistor, the sense circuit capacitor, and the coupling capacitor substantially match a time constant of the first inductor.

16. A method of generating a signal according to claim 13 , wherein selecting the capacitance of the coupling capacitor comprises selecting the capacitance of the coupling capacitor according to a resistance of the first resistor and a DC resistance of the first inductor.

17. A method of generating a signal according to claim 13 , further comprising connecting a first terminal of a second resistor to a first terminal of the sense circuit capacitor and a second terminal of the second resistor to a second terminal of the capacitor, wherein:

a DC impedance of the first resistor, the second resistor, and the sense circuit capacitor substantially match a DC impedance of the inductor; and

the resistance of the first resistor and the resistance of the second resistor are selected according to a desired voltage range of the signal.

18. A method of generating a signal according to claim 17 , wherein the resistance of the first resistor and the resistance of the second resistor are further selected according to a self resistance of the inductor and an anticipated current range through the inductor.