Method and circuits for inductor current measurement in MOS switching regulators

• US 6,377,034 B1
• Filed: 12/11/2000
• Issued: 04/23/2002
• Est. Priority Date: 12/11/2000
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Ivanov, Vadim V.
• Primary Examiner(s): Vu, Bao Q.
• Application Number:
  US09/733,282
• Time in Patent Office: 498 Days
• Field of Search: 323/222, 323/224, 323/268, 323/280, 323/286, 323/287, 323/285, 323/290
• US Class Current: 323/287
• CPC Class Codes: G05F 3/245 producing a voltage or current as a predetermined function of the temperature
• CPC Class Codes: G05F 3/262 using field-effect transistors only
• CPC Class Codes: H03K 2217/0027 Measuring means of, e.g. currents through or voltages across the switch

Abstract

An inductor current measurement circuit (25) accurately measures current supplied to an inductor (17) by a first transistor (2) and/or a second transistor (3). The first transistor (2) has a drain coupled to an input voltage conductor (8), a gate coupled to a switching signal (4), and a source coupled to a the first terminal of an inductor 17. A first sense transistor (7) has a gate and a drain connected to the gate and train, respectively, of the first transistor (2), and a source coupled to a first input of a first amplifier (13) and a drain of a third transistor (12) having a source coupled to a second supply voltage conductor (9), and a gate connected to the gate of a fourth transistor (15). The source of the fourth transistor (15) is connected to the second supply voltage conductive (9) and its drain is connected to an output terminal (18) and a second terminal coupled to the second supply voltage conductor (9). The first transistor (2) and second transistor (3) are included in a DC-DC converter. A second sense transistor (10) has a gate connected to the gate of the second transistor (3) and a drain connected to the drain of the second transistor (3) and to the first terminal of the inductor (17). The source all the second sense transistor (10) is coupled to the output terminal (18). The first and second transistors are operated so that one is on while the other is off, such that the current through the output terminal represents the current through the inductor regardless of which of the first and second transistors supplies the inductor current.

Claims

1. A circuit for measuring current in an inductor, the current being supplied to the inductor by a first transistor or a second transistor, the first and second transistors each having a first electrode, a second electrode, and a control electrode the first transistor having its second electrode coupled to a first conductor, its control electrode coupled to a switching signal and its first electrode coupled to the second electrode of the second transistor and to a terminal of the inductor, the second transistor having its first electrode coupled to a second conductor, the measuring circuit comprising:

(a) a first sense transistor having its control electrode and its second electrode coupled to the control electrode and second electrode, respectively, of the first transistor;

(b) a second sense transistor having its control electrode and its second electrode coupled to the control electrode and second electrode, respectively, of the second transistor;

(c) a first circuit including a third transistor having its second electrode coupled to the first electrode of the first sense transistor and its first electrode coupled to a second conductor, a fourth transistor having its control electrode and its first electrode coupled to the control electrode and the source electrode, respectively, of the third transistor and its first electrode coupled to the summing node, and a first differential amplifier having first and second inputs coupled to the first electrodes of the first transistor and the first sense transistor, respectively, and an output coupled to the control electrode is of the third and forth transistors; and

(d) a second circuit including a fifth transistor having its first electrode coupled to the first electrode of the second sense transistor and to a first input of a second differential amplifier having a second input coupled to the second conductor and an output coupled to the control electrode of the fifth transistor, the fifth transistor having its first electrode coupled to the summing node.

2. A circuit for measuring current in an inductor, the current being supplied to the inductor by a first transistor or a second transistor, the first transistor having a drain coupled to a first conductor, a gate coupled to a switching signal and a source coupled to a drain of the second transistor and to a terminal of the inductor, the second transistor having a source coupled to a second conductor, the measuring circuit comprising:

(a) a first sense transistor having a gate and drain coupled to the gate and drain, respectively, of the first transistor;

(b) a second sense transistor having a gate and drain coupled to the gate and drain, respectively, of the second transistor;

(c) a first circuit including a third transistor having a drain coupled to the source of the first sense transistor and a source coupled to a second conductor, a fourth transistor having a gate and source coupled to the gate and the source, respectively, of the third transistor and a drain coupled to the summing node, and a first differential amplifier having first and second inputs coupled to the sources of the first transistor and the first sense transistor, respectively, and an output coupled to the gates of the third and forth transistors; and

(d) a second circuit including a fifth transistor having a source coupled to the source of the second sense transistor and to pay first input of a second differential amplifier having a second input coupled to the second conductor and an output coupled to a gate of the fifth transistor, the fifth transistor having a drain coupled to the summing node.

3. The current measuring circuit of claim 2 wherein the first and second transistors, first and second sense transistors, and third, fourth and fifth transistors are N-channel transistors.

4. The current measuring circuit of claim 2 wherein the first transistor and the first sense transistor are P-channel transistors.

5. The current measuring circuit of claim 3 wherein the first transistor is a high-side transistor of a switching voltage converter circuit including the inductor, and the second transistor is a low-side transistor of the switching voltage converter circuit.

6. The current measuring circuit of claim 2 including synchronizing circuitry connected to turn the second transistor off while the first transistor is on and vice versa.

7. A switching voltage converter circuit comprising:

(a) an inductor;

(b) a first transistor and a second transistor, the first transistor having a drain coupled to a first conductor, a gate coupled to a switching signal and a source coupled to a drain of the second transistor and to a first terminal of the inductor, the second transistor having a source coupled to a second conductor, a second terminal of the inductor being coupled to an output conductor of the switching voltage converter circuit;

(c) an error amplifier having a first input coupled to the output conductor, a second input coupled to a reference voltage, and an output coupled to a first input of a summing circuit;

(d) a duty cycle modulator circuit having an input coupled to an output of the summing circuit and an output coupled to a driver circuit connected to synchronously drive the gates of the first transistor and second transistor so that one of the first and second transistors is off while the other is on and vice versa;

(e) an inductor current measuring circuit including

I. a first sense transistor having a gate and drain coupled to the gate and drain, respectively, of the first transistor,

ii. a second sense transistor having a gate and drain coupled to the gate and drain, respectively, of the second transistor,

iii. a first circuit including a third transistor having a drain coupled to the source of the first sense transistor and a source coupled to the second conductor, a fourth transistor having a gate and source coupled to the gate and the source, respectively, of the third transistor and a drain coupled to a current summing conductor coupled to a second input of the summing circuit 34A, and a first differential amplifier having first and second inputs coupled to the sources of the first transistor and the first sense transistor, respectively, an output of the first differential amplifier being coupled to gates of the third and fourth transistors, and

iv. a second circuit including a fifth transistor having a source coupled to the source of the second sense transistor and to a first input of a second differential amplifier having a second input coupled to the second conductor and an output coupled to a gate of the fifth transistor, the fifth transistor having a drain coupled to the summing node.

8. An electric motor controller circuit for controlling an electric motor including an inductive winding comprising:

(a) a first transistor and a second transistor, the first transistor having a drain coupled to a first conductor, a gate coupled to a switching signal and a source coupled to a drain of the second transistor and to a first terminal of the winding, the second transistor having a source coupled to a second conductor, a second terminal of the winding being coupled to an output conductor of the electric motor controller circuit;

(b) an error amplifier having a first input coupled to the output conductor, a second input coupled to a reference voltage, and an output coupled to a first input of a summing circuit;

(c) a duty cycle modulator circuit having an input coupled to an output of the summer and an output coupled to driver circuit connected to synchronously drive the gates of the first transistor and second transistor so that one of them is off while the other is on and vice versa;

(d) an current measuring circuit for measuring current in the inductive winding, the current measuring circuit including

I. a first sense transistor having a gate and drain coupled to the gate and drain, respectively, of the first transistor,

ii. a second sense transistor having a gate and drain coupled to the gate and drain, respectively, of the second transistor,

iii. a first circuit including a third transistor having a drain coupled to the source of the first sense transistor and a source coupled to the second conductor, a fourth transistor having a gate and source coupled to the gate and the source, respectively, of the third transistor and a drain coupled to a current summing conductor coupled to a second input of the current summing circuit, and a first differential amplifier having first and second inputs coupled to the sources of the first transistor and the first sense transistor, respectively, an output although first differential amplifier being coupled to gates of the third and forth transistors, and

iv. a second circuit including a fifth transistor having a source coupled to the source of the second sense transistor and to a first input of a second differential amplifier having a second input coupled to the second conductor and an output coupled to a gate of the fifth transistor, the fifth transistor having a drain coupled to the summing node.

9. A method for measuring current in an inductor, the current being supplied to the inductor by a first transistor or a second transistor, the first transistor having a drain coupled to a first conductor, a gate coupled to a switching signal and a source coupled to a drain of the second transistor and to a terminal of the inductor, the second transistor having a source coupled to a second conductor, the measuring method comprising:

(a) operating a first feedback circuit to maintain a source of a first sense transistor having a gate and drain coupled to the gate and the drain, respectively, of the first transistor at the same voltage as the source of the first transistor, and operating a first current mirror circuit to mirror the current in the first sense transistor so as to cause a first mirrored current to flow in a current summing conductor; and

(b) operating a second feedback circuit to maintain the source of a second sense transistor having a gate and a drain coupled to the gate and the drain of the second transistor, respectively, of the second transistor at the same voltage as the source of the second transistor, and operating a second current mirror circuit so as to cause a second mirrored current to flow in the current summing conductor, the sum of the first and second mirrored current representing the current through the inductor.

10. The method of claim 9 wherein step (a) includes coupling a first input of a first differential amplifier to the source of the first transistor, coupling a second input of the first differential amplifier to the source of the first sense transistor, and coupling an output of the first differential amplifier to gate electrodes of a third transistor and a fourth transistor having sources connected to a common conductor and coupling a drain of the of the fourth transistor to the current summing conductor, and wherein step (b) includes coupling the drain of the second transistor to a first input of a second differential amplifier by means of the second sense transistor, the second differential amplifier having a second input coupled to a source of the second transistor and an output coupled to a gate of a fifth transistor, and coupling the fifth transistor between the current summing conductor and the first input of the second differential amplifier.