1 Introduction

Embedded electronics are becoming ever more present in automotive applications, particularly as a means of limiting risk to drivers. With this increasing dependence on electronic systems comes an increasing need to monitor the functioning of these systems to detect potentially critical errors. The purpose of load-diagnostic circuitry is to diagnose potential faults which can occur in electrical circuitry throughout an automobile.

One example application of this circuitry is to support eCall system functionality. The emergency call (eCall) system represents an emerging application in which emergency responders are immediately alerted after an accident through the car phone. The responder is then able to speak with the victim through the audio systems embedded in the car. In the event of an accident, the audio systems of the car can sustain serious damage, preventing a victim from being able to hear instructions issued by emergency responders utilizing the eCall system.

After an accident, there are various faults which can cause the speaker system to fail. Damage from a serious accident can result in short circuits to battery or ground, short circuits across the speaker, or disconnection of the speaker from the audio amplifier. If a failure occurs, it is important that the emergency responders be notified that the victim is unable to hear them. In this instance, load diagnostics are needed to detect potential fault conditions to verify the level of functionality of the system.

While many audio amplifiers have internal diagnostic circuitry, amplifiers such as the TPA3111D1-Q1 have only a basic fault-detection system to detect short-circuit conditions. External circuitry is necessary for these amplifiers to determine the nature of the fault which has occurred. The object of the design presented within this application note is to provide a possible external fault diagnostic circuit topology as an alternative to chips possessing internal fault diagnostics.

The circuit and design presented in this application note has not been tested to any industry standards. It is the responsibility of the reader to perform standard industry testing to assure safety when using the design in part or in whole in any form. Texas Instruments does not provide any guarantees, written or implied, about the safety of the design.