Load current detection techniques for discontinuous conduction mode

1. A method for real-time load current detection for a switching converter using a discontinuous conduction mode (DCM) of operation, the method comprising:

generating a minimum DCM current threshold based on an reference current source and a duty cycle of the switching converter;

receiving a representation of inductor charge current from power switch of the switching converter at a comparator;

comparing the representation to the DCM current threshold; and

controlling the power switch using a discontinuous conduction mode of the switching converter when a peak of the representation exceeds the minimum DCM current threshold.

2. The method of claim 1 , including switching from the discontinuous conduction mode of operation of the converter when the representation does not exceed the minimum DCM current threshold.

3. The method of claim 1 , wherein the generating the minimum DCM current threshold includes mirroring the minimum DCM current threshold via a feedback path, the feedback path including a feedback resistor and a duty-cycle switch configured to operate according to a duty cycle (D) of the converter.

4. The method of claim 3 , including comparing a feedback voltage across the feedback resistor to a reference voltage across a reference resistor to provide a minimum DCM current control signal.

5. The method of claim 4 , wherein the comparing the feedback voltage to a reference voltage includes providing a reference current to the reference resistor from the reference current source.

6. The method of claim 5 , wherein the receiving the representation of an inductor charge current includes scaling the inductor current by a factor of K using a current sensor.

7. The method of claim 4 , wherein generating the minimum DCM current threshold (I th ) includes setting the minimum DCM current threshold as a function of the reference current (I ref ) provided by the adjustable current source such that,

I

th

=

I

ref

*

R

⁢

⁢

2

DR

⁢

⁢

1

.

8. A circuit for changing an operating mode of a discontinuous conduction mode voltage converter, the circuit comprising:

a first comparator configured to compare a representation of a contemporaneous current load of the voltage converter with a minimum DCM current threshold, and to provide an output signal indicative of the comparison; and

a threshold generator circuit configured to provide the minimum DCM current threshold based on a reference current and a duty cycle of the converter.

9. The circuit of claim 8 , wherein the first comparator is configured to receive a scaled representation of an inductor current of the converter from a current sensor associated with a power switch of the converter, the scaled representation having a scale factor of K.

10. The circuit of claim 9 , wherein the threshold generator circuit includes a first current mirror configured to provide the minimum DCM current threshold to a second input of the comparator.

11. The circuit of claim 10 , wherein the threshold generator circuit includes a second current mirror configured to feedback a representation of the minimum DCM current threshold to a feedback path of the threshold generator.

12. The circuit of claim 11 , wherein the feedback path includes a switch configured to operate according to a duty cycle of the converter and a feedback resistor coupled to the switch and configured to provide a feedback voltage.

13. The circuit of claim 12 , wherein the threshold generator circuit includes a second comparator configured to compare the feedback voltage with a reference voltage and to provide a DCM threshold current control signal.

14. The circuit of claim 13 , wherein the threshold generator circuit includes a reference current source configured to provide the reference current and a reference resistor configured to provide a reference voltage using the reference current.

15. The circuit of claim 13 , wherein the threshold generator circuit includes an output transistor configure to receive the DCM threshold current control signal and to generate the minimum DCM current threshold.

16. A switching converter comprising:

an input configured to receive and input voltage;

an output configured to provide an output voltage to a load;

a power switch coupled to the input;

an inductor coupled to the output, wherein the power switch and the inductor are coupled in series with each other between the input and the output;

a current sensor configured to provide a representation of current passing through the power switch; and

a control circuit configured to control the power switch in one of a plurality of modes;

wherein the control circuit includes:

a threshold generator circuit configured to provide a minimum DCM threshold based on a reference current and a duty cycle of the power switch of the switching converter; and

a first comparator configured to compare the representation with the minimum DCM threshold, and to provide an output signal indicative of the comparison; and

wherein the control circuit controls the power switch in a discontinuous current mode of the plurality of modes when the representation exceeds the minimum DCM threshold.

17. The switching converter of claim 16 , wherein the control circuit is configured to receive a scaled representation of an inductor current of the converter from the current sensor, the scaled representation having a scale factor of K.

18. The switching converter of claim 17 , wherein the threshold generator circuit includes:

a first current mirror configured to provide the minimum DCM threshold to a second input of the comparator; and

a second current mirror configured to feedback a representation of the minimum DCM threshold to a feedback path of the threshold generator.

19. The switching converter of claim 17 , wherein the feedback path includes a switch configured to operate according to a duty cycle of the converter and a feedback resistor coupled to the switch and configured to provide a feedback voltage.

20. The switching converter of claim 19 , wherein the threshold generator circuit includes:

a second comparator configured to compare the feedback voltage with a reference voltage and to provide a DCM threshold current control signal; and

a reference current source configured to generate the reference voltage in cooperation with a second resistor.