# US 9,520,840 B2 · Current limiter

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- Number: US 9,520,840 B2
- Document ID: US9520840B2
- Status: Granted
- Kind: B2
- Application number: 14/597,940
- Filed: 2015-01-15
- Published: 2016-07-21
- Granted: 2016-12-13
- Earliest claimed: 2015-01-15
- Assignees: NXP B.V.
- Applicants: NXP B.V.
- Inventors: Mattheus Johan Koerts; Fred Mostert; Fre Jorrit Jorritsma
- Web page: https://patentgrep.com/patent/US9520840B2

## CPC

- H03F 1/523: {for amplifiers using field-effect devices (H03F1/526 takes precedence)}
- H03F 1/52: Circuit arrangements for protecting such amplifiers {(monitoring arrangements G01R31/28; increasing reliability in communication systems, e.g. using redundancy H04B1/74)}
- H03F 3/183: with semiconductor devices only
- H03F 3/211: {using a combination of several amplifiers (H03F3/60 takes precedence)}
- H03F 3/2171: {with field-effect devices (H03F3/2173 - H03F3/2178 take precedence)}
- H03F 3/2173: {of the bridge type}
- H03F 2200/03: the amplifier being designed for audio applications
- H03F 2200/351: Pulse width modulation being used in an amplifying circuit
- H03F 2203/21139: An impedance adaptation circuit being added at the output of a power amplifier stage
- H03F: AMPLIFIERS

## Abstract

A current limiter for Class-D amplifiers measures and stores a position of an over-current event. By comparing the stored position, output signals can be selectively inverted. As a result, the Class-D amplifier remains in a defined modulation scheme even during period of current limiting.

## Claims

### Claim 1

A current limiter for a class D amplifier, the current limiter comprising:
an over-current protection (OCP) block coupled to both a first side and a second side of the class D amplifier, wherein the OCP block further comprises:
a plurality of over-current detecting (OCD) inputs;
a plurality of OCP count blocks coupled to the plurality of OCD inputs;
an OCP minimum position block coupled to the plurality of OCP count blocks; and
a plurality of comparators coupled to the OCP minimum position block and configured to receive a plurality of running event position signals.

### Claim 2 (depends on 1)

The current limiter of claim 1, wherein at least one OCD input of the plurality of OCD inputs further comprises a spike filter, wherein at least one spike filter is coupled between a respective OCD input and a respective OCP count block.

### Claim 3 (depends on 1)

The current limiter of claim 1, wherein at least one OCP count block of the plurality of OCP count blocks is configured to measure an OCD event position.

### Claim 4 (depends on 3)

The current limiter of claim 3, wherein at least one OCP count block of the plurality of OCP count blocks is configured to store the measured OCD event position.

### Claim 5 (depends on 1)

The current limiter of claim 1, wherein the OCP minimum position block is configured to select an OCD event position from the plurality of OCP count blocks.

### Claim 6 (depends on 5)

The current limiter of claim 5, wherein the OCP minimum position block is configured to select the most stringent OCD event position.

### Claim 7 (depends on 1)

The current limiter of claim 1, wherein at least one comparator of the plurality of comparators is configured to compare a selected OCD event position from the OCP minimum position block with a particular running event position.

### Claim 8 (depends on 7)

The current limiter of claim 7, wherein at least one comparator of the plurality of comparators is configured to generate an invert signal that flags which output of a respective block in the class D amplifier needs to be inverted.

### Claim 9

A method of limiting currents for a class D amplifier, the method comprising:
detecting an over-current event;
storing a position of the over-current event as an OCD position;
comparing the stored OCD position to a PWM carrier position; and
inverting a PWM signal when the PWM carrier position is equal to the stored OCD position.

### Claim 10 (depends on 9)

The method of claim 9, further comprising:
measuring a plurality of OCD positions.

### Claim 11 (depends on 10)

The method of claim 10, further comprising:
comparing the plurality of measured OCD positions to a threshold; and
selecting a most stringent OCD position from the plurality of measured OCD positions.

### Claim 12 (depends on 10)

The method of claim 10, further comprising:
measuring the plurality of OCD positions with a sample and hold technique.

### Claim 13 (depends on 9)

The method of claim 9, further comprising:
using a spike filter on input data before detecting the over-current event.

### Claim 14 (depends on 9)

The method of claim 9, further comprising:
comparing a selected OCD position with a particular running event position.

### Claim 15 (depends on 9)

The method of claim 9, further comprising:
holding the stored OCD position for two PWM carrier edges.

### Claim 16 (depends on 9)

The method of claim 9, further comprising:
comparing a duty cycle to a predetermined threshold.

### Claim 17 (depends on 16)

The method of claim 16, further comprising:
determining, when the duty cycle exceeds the predetermined threshold, that a short circuit is present.