System and method for high precision current sensing

• US 9,088,208 B2
• Filed: 07/21/2010
• Issued: 07/21/2015
• Est. Priority Date: 01/27/2010
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Isham, Robert H., Wang, Jue
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): LEE III, HENRY E
• Application Number:
  US12/840,958
• Publication Number:
  US 20110181253A1
• Time in Patent Office: 1,826 Days
• Field of Search: 323/301, 323/247
• US Class Current: 1/1
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

An apparatus for sensing an input current through an inductor includes an RC circuit connected in parallel with the inductor across first and second input pins of an integrated circuit. A voltage monitoring circuit monitors a first voltage at the first input pin of the integrated circuit and monitors a second voltage at the second input pin of the integrated circuit. An op-amp compares the first voltage with the second voltage and generates a control output responsive to the comparison. A current sink circuit responsive to the indication controls the first voltage to substantially equal the second voltage.

Claims

1. An apparatus for sensing an input current of a voltage regulator supplied through an inductor, the apparatus comprising:

an RC circuit configured for connection in parallel with the inductor;

an integrated circuit including first and second input pins, the RC circuit also connected across the first and second input pins, the integrated circuit further including,

a voltage monitoring circuit for monitoring a first voltage at the first input pin of the integrated circuit and for monitoring a second voltage at the second input pin of the integrated circuit;

an op-amp for comparing the first voltage with the second voltage and generating a control output responsive to the comparison; and

a current sink circuit operable responsive to the control output to sink a current for controlling the first voltage to substantially equal the second voltage, wherein the value of the current that the current sink circuit sinks is proportional to the input current through the inductor.

2. The apparatus of claim 1, wherein the voltage monitoring circuit further comprises:

a current mirror for generating the first voltage and the second voltage, the current mirror comprising;

first voltage generation circuitry for monitoring the first voltage at the first input pin;

second voltage generation circuitry for monitoring the second voltage at the second input pin;

bias circuitry for generating a bias voltage for the first voltage generation circuitry and the second voltage generation circuitry.

3. The apparatus of claim 1, wherein the current sink circuit is configured to sink a current from the first input pin in a first mode of operation responsive to a determination that the first voltage exceeds the second voltage, and is configured not to sink the current from the first input pin in a second mode of operation responsive to a determination that the first voltage substantially equals the second voltage.

4. The apparatus of claim 1, wherein at least one additional current sink circuit is connected to the output of the operational amplifier.

5. The apparatus of claim 1, wherein the RC circuit further comprises:

a first resistor connected to a first end of the inductor;

a capacitor in series with the first resistor and connected to the second end of the inductor; and

a second resistor connected between the connection of the first resistor and the capacitor and the first input pin.

6. The apparatus of claim 5 wherein the current through the first resistor and the second resistor into the first input pin is proportional to the current through the inductor.

17. The apparatus of claim 3, wherein the current sink further comprises:

a resistor;

a transistor connected between the first input pin and resistor; and

wherein when the transistor is controlled by the control output of the operational amplifier to attempt to have the first voltage associated with the first input pin substantially equal the second voltage associated with the second input pin.

7. An apparatus, comprising:

a voltage regulation circuit for generating an output voltage responsive to an input voltage, the voltage regulation circuit comprising;

switching transistors; and

an output filter including an output inductor and a capacitor;

an input inductor connected between an input power supply and the voltage regulation circuit;

current sensing circuitry for sensing an input current through the input inductor of the voltage regulator, the current sensing circuitry comprising;

an RC circuit connected in parallel with the inductor across first and second input pins of an integrated circuit;

a voltage monitoring circuit for monitoring a first voltage at the first input pin of the integrated circuit and for monitoring a second voltage at the second input pin of the integrated circuit;

a comparing circuit for comparing the first voltage with the second voltage and generating a control output responsive to the comparison; and

a current sink circuit responsive to the control output for controlling the first voltage to substantially equal the second voltage, wherein the current sink circuit is configured to sink a current having a value indicating the value of the input current through the input inductor.

8. The apparatus of claim 7, wherein the voltage monitoring circuit further comprises:

a current mirror for generating the first voltage and the second voltage, the current mirror comprising;

first voltage generation circuitry for monitoring the first voltage at the first input pin; and

second voltage generation circuitry for monitoring the second voltage at the second input pin; and

bias circuitry for generating a bias voltage for the first voltage generation circuitry and the second voltage generation circuitry.

9. The apparatus of claim 7, wherein the current sink circuit is configured to sink a current from the first input pin in a first mode of operation responsive to a determination that the first voltage exceeds the second voltage, and is configured not to sink the current from the first input pin in a second mode of operation responsive to a determination that the first voltage substantially equals the second voltage.

10. The apparatus of claim 7, wherein at least one additional current sink circuit is connected to the output of the operational amplifier.

11. The apparatus of claim 7, wherein the RC circuit further comprises:

a first resistor connected to a first end of the inductor;

a capacitor in series with the first resistor and connected to a second end of the inductor; and

a second resistor connected between the connection of the first resistor and the capacitor and the first input pin.

12. The apparatus of claim 11, wherein the current through the first resistor and the second resistor into the first input pin is proportional to the current through the inductor.

18. The apparatus of claim 9, wherein the current sink further comprises:

a resistor;

a transistor connected between the first input pin and resistor; and

wherein when the transistor is configured to be controlled by the control output of the operational amplifier to attempt to have the first voltage associated with the first pin substantially equal the second voltage associated with the second pin.

13. A method for sensing an input current through an inductor,

the method comprising:

generating a first voltage and a second voltage, the difference between the two voltages being representative of an input current through the inductor using an RC circuit connected in parallel with the inductor across a first and second input pins of an integrated circuit;

monitoring the first voltage at the first input pin of the integrated circuit and the second voltage at the second input pin of the integrated circuit;

comparing the first voltage with the second voltage;

generating a control output responsive to the comparison; and

sinking a current from the first input pin responsive to the control output to adjust the first voltage to be approximately equal to the second voltage, wherein the value of the current being sinked indicates the value of the input current through the inductor.

14. The method of claim 13, wherein the step of monitoring further comprises the step of generating the first voltage responsive to the monitored first voltage and the second voltage responsive to the monitored second voltage.

15. The method of claim 13, wherein the step of sinking further comprises the step of driving a current sink responsive to the control output in a first mode of operation to initiate sinking the current from the first input pin.

16. The method of claim 13, further comprising the step of limiting a current from a current sink responsive to the control output in a second mode of operation.

19. The method of claim 13, further comprising:

sinking a current from the first input pin in a first mode of operation responsive to the control output indicating that the first voltage exceeds the second voltage; and

controlling sinking of the current from the first input pin in a second mode of operation responsive to the control input indicating that the first voltage substantially equals the second voltage.

20. An integrated circuit operable to sense an input current of a voltage regulator, the integrated circuit comprising:

a first input pin and a second input pin, the first and second input pins adapted to have an input inductor coupled across the first and second input pins and an RC circuit coupled in parallel with the input inductor across the first and second input pins;

a voltage detection circuit operable to detect a first voltage on the first input pin of the integrated circuit and to detect a second voltage on the second input pin of the integrated circuit, the voltage detection circuit operable to generate a control signal responsive to the difference between the first and second voltages; and

a current sensing circuit operable responsive to the control signal to sink a sense current from the first input pin, the sense current having a value that causes the first voltage to be approximately equal to the second voltage and the value of the sense current indicating the value of a current through the input inductor.