Patent ID: 7705673

Claim:
An apparatus for detecting an over-current condition in a class D output stage having a high side FET and a low side FET coupled together between nodes of a power supply, the apparatus comprising: a narrow pulse detector coupled to a pulse-width-modulated (PWM) signal input of a deadtime control circuit operable to drive the FETs of the class D output stage, the narrow pulse detector operable to provide an output indicative of a narrow pulse condition if the pulse width of the PWM signal at the input of the deadtime control circuit falls below a predetermined width threshold; and a negative current sensor coupled to the low side FET in the class D output stage, wherein the negative current sensor includes a current sense and threshold comparator, and wherein the negative current sensor has an output coupled to over-current protection logic, and wherein during a condition of the PWM signal having a pulse width below the predetermined width threshold, the negative current sensor measures the negative current flow through the low side FET during its conduction time, compares the measured negative current to a first predetermined current threshold, and provides a signal to over-current protection logic indicative of the current exceeding or not exceeding the first predetermined current threshold.