Sensing current of a DC-DC converter

1. A current sensor for a DC (‘Direct Current’)-DC converter, the DC-DC converter comprising:

a directly coupled inductor comprising a plurality of coil elements; and

a plurality of power-switching phases, each power-switching phase coupled to a different one of the plurality of coil elements, each phase comprising: a high-side switch and a low-side switch, wherein the high-side switch is configured, when activated, to couple a voltage source to one of the coil elements and the low-side switch is configured, when activated, to couple the coil element to a ground voltage, wherein each switch of the DC-DC converter is configured to be alternately activated and no two switches are activated at the same time;

the current sensor comprising:

a single current amplifier comprising a plurality of inputs and an output, wherein the output provides a current sensing signal;

a single RC network (Resistor-Capacitor network') coupled to one of the power-switching phases and a first input of the current amplifier, the RC network comprising a resistor in series with a capacitor; and

a resistive ladder comprising: for each of the other power-switching phases, a resistor coupled in parallel to the resistor of the RC network and coupled to a second input of the current amplifier.

2. The current sensor of claim 1 wherein the DC-DC converter further comprises a filter and a load coupled to the directly coupled inductor and each switch of the DC-DC converter is configured to be alternately activated by:

activating the high-side switch of a first power-switching phase, including coupling the voltage source to a first coil element, energizing a magnetic core of the directly coupled inductor, and providing, via the first coil element, output current to the filter and load;

activating the low-side switch of the first power-switching phase, including coupling the first coil element to the ground voltage and providing, via a second coil element and the energized magnetic core, output current to the filter and load;

activating the high-side switch of a second power-switching phase, including coupling the voltage source to the second coil element, re-energizing the magnetic core of the directly coupled inductor, and providing, via the second coil element, output current to the filter and load; and

activating the low-side switch of the second power-switching phase, including coupling the second coil element to the ground voltage and providing, via the first coil element and the energized magnetic core, output current to the filter and load.

3. The current sensor of claim 1 wherein each switch of the DC-DC converter is configured to be alternately activated and no two switches are activated at the same time by:

activating each high-side switch for a period of time according to:

D

N

where D represents a duty cycle and N represents the number of power-switching phases; and

activating each low-side switch for a period of time according to:

(

1

-

D

)

N

.

4. The current sensor of claim 1 wherein the number of power-switching phases is inversely proportional to the duty cycle of activating the switches and thereby inversely proportional to the inductance of the directly coupled inductor.

5. The current sensor of claim 1 wherein the DC-DC converter further comprises a filter and a load coupled to the directly coupled inductor and current ripple experienced by the filter and the load comprises:

1

f

*

⁢

L

OL

*

(

1

-

V

OUT

V

IN

)

*

V

OUT

N

,

where f represents the frequency of alternatively activating each switch, L OL represents the open loop inductance of the directly coupled inductor, N represents the number of power-switching phases, V IN represents the voltage of the voltage source and V OUT represents the voltage experienced at the filter and load.

6. The current sensor of claim 1 wherein each high-side switch and each low-side switch comprises a Field Effect Transistor.

7. A method of sensing current of a DC (‘Direct Current’)-DC converter, the DC-DC converter comprising:

a directly coupled inductor comprising a plurality of coil elements; and

a plurality of power-switching phases, each power-switching phase coupled to a different one of the plurality of coil elements, each phase comprising: a high-side switch and a low-side switch, wherein the high-side switch is configured, when activated, to couple a voltage source to one of the coil elements and the low-side switch is configured, when activated, to couple the coil element to a ground voltage, wherein each switch of the DC-DC converter is configured to be alternately activated and no two switches are activated at the same time; and

the method comprises:

measuring a current sensing signal provided by a current sensor, wherein the current sensor comprises:

a single current amplifier comprising a plurality of inputs and an output, wherein the output provides the current sensing signal;

a single RC network (‘Resistor-Capacitor network’) coupled to one of the power-switching phases and a first input of the current amplifier, the RC network comprising a resistor in series with a capacitor; and

a resistive ladder comprising: for each of the other power-switching phases, a resistor coupled in parallel to the resistor of the RC network and coupled to a second input of the current amplifier.

8. The method of claim 7 wherein the DC-DC converter further comprises a filter and a load coupled to the directly coupled inductor and each switch of the DC-DC converter is configured to be alternately activated by:

activating the high-side switch of a first power-switching phase, including coupling the voltage source to a first coil element, energizing a magnetic core of the directly coupled inductor, and providing, via the first coil element, output current to the filter and load;

activating the low-side switch of the first power-switching phase, including coupling the first coil element to the ground voltage and providing, via a second coil element and the energized magnetic core, output current to the filter and load;

activating the high-side switch of a second power-switching phase, including coupling the voltage source to the second coil element, re-energizing the magnetic core of the directly coupled inductor, and providing, via the second coil element, output current to the filter and load; and

activating the low-side switch of the second power-switching phase, including coupling the second coil element to the ground voltage and providing, via the first coil element and the energized magnetic core, output current to the filter and load.

9. The method of claim 7 wherein each switch of the DC-DC converter is configured to be alternately activated and no two switches are activated at the same time by:

activating each high-side switch for a period of time according to:

D

N

where D represents a duty cycle and N represents the number of power-switching phases; and

activating each low-side switch for a period of time according to:

(

1

-

D

)

N

.

10. The method of claim 7 wherein the number of power-switching phases is inversely proportional to the duty cycle of activating the switches and thereby inversely proportional to the inductance of the directly coupled inductor.

11. The method of claim 7 wherein the DC-DC converter further comprises a filter and a load coupled to the directly coupled inductor and current ripple experienced by the filter and the load comprises:

1

f

*

⁢

L

OL

*

(

1

-

V

OUT

V

IN

)

*

V

OUT

N

,

where f represents the frequency of alternatively activating each switch, L OL represents the open loop inductance of the directly coupled inductor, N represents the number of power-switching phases, V IN represents the voltage of the voltage source and V OUT represents the voltage experienced at the filter and load.

12. The method of claim 7 wherein each high-side switch and each low-side switch comprises a Field Effect Transistor.