Output Short Circuit and Load Detection

• US 20090322426A1
• Filed: 06/30/2008
• Published: 12/31/2009
• Est. Priority Date: 06/30/2008
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Krogsgaard, Klaus, Nyboe, Flemming
• Granted Patent: US 7,889,011 B2
• Time in Patent Office: Days
• US Class Current: 330/251
• CPC Class Codes: H03F 1/52 Circuit arrangements for protecting such amplifiers monitoring arrangements G01R31/28; increasing reliability in communication systems, e.g. using redundancy H04B1/74
• 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

One embodiment of an apparatus for testing an amplifier includes an amplifier having a driver and a filter, the filter being connected between an output of the driver and an output of the amplifier. The filter is operable to produce a demodulated output signal from a higher frequency modulated signal at the driver output. The apparatus also includes a voltage level detector connected to the driver output and a control circuit operable to detect at least one fault based on a voltage level measured at the driver output by the voltage level detector.

Claims

1. An apparatus for testing an amplifier, the apparatus comprising:

an amplifier comprising a driver and a filter, the filter being connected between an output of the driver and an output of the amplifier, the filter being operable to produce a demodulated output signal from a higher frequency modulated signal at the driver output;

a voltage level detector connected to the driver output; and

a control circuit operable to detect at least one fault based on a voltage level measured at the driver output by the voltage level detector.

2. The apparatus of claim 1, wherein the control circuit is operable to test the amplifier when power has been applied to the driver and before an input signal has been applied to the driver.

3. The apparatus of claim 1, further comprising a gate driver connected to a control input of the driver, wherein the control circuit is operable to test the amplifier when power has been applied to the gate driver and before an input signal has been applied to the driver.

4. The apparatus of claim 3, wherein the control circuit is operable to detect whether a short to a lower power supply rail prevents the voltage level at the driver output from rising due to the power applied to the gate driver.

5. The apparatus of claim 1, further comprising a pulldown switch connected between the driver output and a lower power supply rail.

6. The apparatus of claim 5, further comprising a resistor connected between the pulldown switch and the lower power supply rail.

7. The apparatus of claim 5, wherein the pulldown switch comprises a transistor having a gate connected to the control circuit, the control circuit being operable to turn on the transistor to pull the driver output down to the lower power supply rail and to determine whether the driver output is held above a reference voltage level by a short to an upper power supply rail.

8. The apparatus of claim 1, wherein the voltage level detector comprises a comparator having a first input connected to the driver output, a second input connected to a reference voltage source, and an output connected to the control circuit.

9. The apparatus of claim 5, further comprising:

a second driver and second filter, the second filter being connected between an output of the second driver and a second output of the amplifier, wherein a load may be connected between the amplifier output and the second amplifier output; and

a second voltage level detector connected to the output of the second driver, wherein the control circuit is operable to detect the load connected between the amplifier output and the second amplifier output by turning on the pulldown switch and measuring a voltage level on at least one of the driver output and second driver output.

10. The apparatus of claim 1, wherein the control circuit is operable to disable the amplifier if the at least one fault is detected.

11. The apparatus of claim 1, the driver comprising a plurality of transistors connected in series between an upper and a lower power supply rail, where the driver output comprises a node between the plurality of transistors.

12. A method of testing an amplifier, the method comprising:

applying power to a high side gate driver and output transistors in a class D amplifier;

measuring a voltage level at a test node at an output of an output stage driver and an input of an output filter, and;

determining a presence of at least one type of fault associated with the class D amplifier based at least in part on the voltage level measured at the test node.

13. The method of claim 12, wherein the measuring and determining is performed without an input signal applied to the output stage driver.

14. The method of claim 12, further comprising disabling the class D amplifier if the presence of at least one type of fault is detected.

15. The method of claim 12, the determining comprising identifying whether a short to a lower power supply rail exists and prevents the voltage level at the test node from being pulled above a reference voltage by the high side gate driver.

16. The method of claim 12, further comprising pulling the test node down toward a lower power supply rail, the determining comprising identifying whether a short to an upper power supply rail exists and prevents the voltage level at the test node from being pulled below a reference voltage.

17. The method of claim 12, the amplifier comprising a second test node at an output of a second output stage driver and an input of a second output filter, the output filter and the second output filter being connected in an H bridge, the method further comprising pulling the test node down to a lower power supply rail and determining whether a voltage level at the second test node falls below a reference voltage.

18. The method of claim 17, further comprising determining whether a voltage level at the test node falls below a second reference voltage, wherein the second reference voltage is lower than the reference voltage.

19. The method of claim 18, further comprising pulling the second test node down toward the lower power supply rail and determining whether the voltage level at the second test node falls below the reference voltage.

20. An audio device comprising:

a class D amplifier having a driver and a filter, the filter being connected between an output of the driver and an output of the amplifier, the filter being operable to produce a demodulated output signal from a higher frequency modulated signal at the driver output;

a voltage level detector connected to the driver output;

a pulldown switch connected between the driver output and a lower power supply rail, and;

a control circuit operable to detect at least one fault based on a voltage level measured at the driver output by the voltage level detector, wherein the control circuit is operable to detect whether a short to the lower power supply rail prevents the voltage level at the driver output from rising above a reference voltage level due to power applied to the driver, and wherein the control circuit is further operable to turn on the pulldown switch to pull the driver output down to the lower power supply rail and to determine whether the driver output is held above the reference voltage level by a short to an upper power supply rail.

21. An apparatus for testing an amplifier, the apparatus comprising:

an amplifier comprising a driver and a filter, the filter being connected between an output of the driver and an output of the amplifier, the filter being operable to produce a demodulated output signal from a higher frequency modulated signal at the driver output;

a voltage level comparator having a first input connected to the driver output, a second input connected to a reference voltage source, and an output connected to the control circuit;

a gate driver connected to a control input of the driver;

a control circuit operable to detect at least one fault based on a voltage level measured at the driver output by the voltage level comparator;

a pulldown switch connected between the driver output and a lower power supply rail, the pulldown switch comprising a transistor having a gate connected to the control circuit;

a resistor connected between the pulldown switch and the lower power supply rail;

a second driver and second filter, the second filter being connected between an output of the second driver and a second output of the amplifier, wherein a load may be connected between the amplifier output and the second amplifier output; and

a second voltage level detector connected to the output of the second driver, wherein the control circuit is operable to detect the load connected between the amplifier output and the second amplifier output by turning on the pulldown switch and measuring a voltage level on at least one of the driver output and second driver output.