SLYT869 November   2025 INA180-Q1 , TAS5431-Q1

 

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  2. 12
  3. 2Real Time Diagnostics (RTD)
  4. 3Class-D amplifier selection
  5. 4Achieving RTD
  6. 5Additional considerations
  7. 6Conclusion

2 Real Time Diagnostics (RTD)

As an additional layer of safety, some vehicle manufacturers are requiring real-time diagnostics (RTD). Traditionally, Class-D speaker diagnostics check the speaker when the TCU module or Class-D amplifier turns on but will not monitor thereafter for all fault scenarios. RTD monitors the speaker at startup and continues to monitor it while the vehicle is in operation. This additional monitoring not only reduces the time between system failure and notification but also ensures prompt notification during events such as a lengthy hundred-mile drive.

Immediately alerting the driver minimizes the chance of an accident occurring while the emergency call speaker is in a faulty condition. Additionally, the system can also alert emergency service operators during an emergency phone call if a speaker fault issue is detected. If the speaker experiences a fault after a car accident (such as severed wires between the TCU module and the speaker), the system can send a message to the emergency operator that the driver will not be able to hear their commands. As a final requirement, diagnostics should never introduce errant audio in the cabin.

The Class-D amplifier must be able to diagnose four main speaker fault conditions, as shown in the following figures.

The four speaker fault conditions: open speaker or load (a); positive output shorted to a negative output (b); positive output or negative output shorted to ground (c); positive output or negative output shorted to the vehicle battery (d). Figure 2 The four speaker fault conditions: open speaker or load (a); positive output shorted to a negative output (b); positive output or negative output shorted to ground (c); positive output or negative output shorted to the vehicle battery (d).

Additionally, the Class-D amplifier should be able to operate normally even when a fault is removed without requiring host intervention. For example, it should be possible to detect an intermittent short on the speaker wires; however, the system still operates normally when the fault condition is removed.