CLASS-D AMPLIFIER CIRCUIT

• US 20180076781A1
• Filed: 09/15/2017
• Published: 03/15/2018
• Est. Priority Date: 09/15/2016
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: KOYAMA, Yasuyuki
• Granted Patent: US 10,367,459 B2
• Time in Patent Office: Days
• CPC Class Codes: H03F 1/523 for amplifiers using field-effect devices H03F1/526 takes precedence
• CPC Class Codes: H03F 2200/03 the amplifier being designed for audio applications
• CPC Class Codes: H03F 2200/171 A filter circuit coupled to the output of an amplifier
• CPC Class Codes: H03F 2200/351 Pulse width modulation being used in an amplifying circuit
• CPC Class Codes: H03F 2200/426 the amplifier comprising circuitry for protection against overload
• CPC Class Codes: H03F 2200/462 the current being sensed
• CPC Class Codes: H03F 3/187 in integrated circuits
• CPC Class Codes: H03F 3/2171 with field-effect devices H03F3/2173 - H03F3/2178 take precedence
• CPC Class Codes: H03F 3/2173 of the bridge type

Abstract

A bridge output stage is coupled to an electroacoustic conversion element via an inductor L. Driving circuits drive the output stage according to pulse signals S_2H and S_2L that correspond to an audio signal S₁. An overcurrent detection circuit asserts an overcurrent detection signal S_3L when a current I_ML that flows through a transistor M_L to be monitored that forms the output stage is continuously larger than a first threshold value for a first period of time or when the current I_ML that flows through the transistor M_L to be monitored is larger than a second threshold value that is higher than the first threshold value after a predetermined second period of time elapses after the transistor M_L to be monitored turns on.

Claims

1. A Class-D amplifier circuit comprising:

a bridge output stage coupled to an electroacoustic conversion element via an inductor;

a driving circuit structured to drive the output stage according to a pulse signal that corresponds to an audio signal; and

an overcurrent detection circuit structured to assert an overcurrent detection signal (i) when a current that flows through a transistor to be monitored that forms the output stage exceeds a first threshold value for a predetermined first period of time, or (ii) when a current that flows through the transistor to be monitored exceeds a second threshold value that is higher than the first threshold value after a predetermined second period of time elapses after the transistor to be monitored turns on.

2. The Class-D amplifier circuit according to claim 1, wherein the transistor to be monitored is turned off according to an assertion of the overcurrent detection signal.

3. The Class-D amplifier circuit according to claim 1, wherein, when a predetermined number of cycles of assertions of the overcurrent detection signal consecutively occur, switching of the output stage is suspended.

4. The Class-D amplifier circuit according to claim 1, structured to be capable of outputting the overcurrent detection signal to an external circuit.

5. The Class-D amplifier circuit according to claim 1, wherein the overcurrent detection circuit comprises:

a first comparator structured to compare a current detection signal that corresponds to a current that flows through the transistor to be monitored with a first threshold voltage that corresponds to the first threshold value, and to generate a first comparison signal indicating a comparison result;

a second comparator structured to compare the current detection signal with a second threshold voltage that corresponds to the second threshold value, and to generate a second comparison signal indicating a comparison result; and

a judgment circuit structured to generate the overcurrent detection signal based on the first comparison signal and the second comparison signal.

6. The Class-D amplifier circuit according to claim 5, wherein the current detection signal corresponds to a voltage drop across the transistor to be monitored.

7. The Class-D amplifier circuit according to claim 1, wherein a high-side transistor and a low-side transistor are both set to be the transistor to be monitored.

8. The Class-D amplifier circuit according to claim 1, wherein the output stage is configured as a full-bridge circuit.

9. The Class-D amplifier circuit according to claim 1, monolithically integrated on a single semiconductor substrate.

10. An audio output device comprising:

an electroacoustic conversion element;

the Class-D amplifier circuit according to claim 1; and

a filter circuit comprising an inductor arranged between the Class-D amplifier circuit and the electroacoustic conversion element.

11. An electronic device comprising:

an electroacoustic conversion element;

the Class-D amplifier circuit according to claim 1; and

a filter circuit comprising an inductor arranged between the Class-D amplifier circuit and the electroacoustic conversion element.

12. A control method for a Class-D amplifier circuit coupled to an electroacoustic conversion element via an inductor, the control method comprising:

generating a pulse signal that corresponds to an audio signal;

driving an output stage of the audio Class-D amplifier according to the pulse signal; and

asserting an overcurrent detection signal (i) when a current that flows through a transistor to be monitored that forms the output stage exceeds a first threshold value for a predetermined first period of time, or (ii) when a current that flows through the transistor to be monitored exceeds a second threshold value that is higher than the first threshold value after a predetermined second period of time elapses after the transistor to be monitored turns on.

13. The control method according to claim 12, further comprising suspending switching of the output stage when a predetermined number of cycles of assertions of the overcurrent detection signal consecutively occur.