The instrument cluster is the main means to display information and status of vehicle systems and drive conditions. What was once a basic display, now includes gauges for various parameters, indicators and status lights as well as displays and sometimes sophisticated acoustical effects.
Depending on the target customer base, the instrument cluster audio subsystem can be implemented in multiple ways. Higher-end systems prioritize higher sound pressure level (SPL), audio quality and reliability, while cost is a top priority in lower-end systems.
SPL
Higher SPL helps overcome interior noise, particularly at high road speeds. SPL is directly related to the output power delivered by the speaker and to the output power delivered by the audio amplifier. At constant speaker impedance, the power delivered to the speaker by the amplifier depends on the amplifier’s efficiency and voltage.
- In terms of efficiency, Class-D amplifiers have the upper hand (compared to Class-AB amplifiers). Class-D amplifiers can deliver substantially higher efficiency levels in the 80-90 percent range, whereas Class-AB amplifiers can deliver 30-40 percent and require more complex thermal management.
- A higher-voltage amplifier typically delivers more power and is more likely to withstand the high-voltage transients typical in automotive systems.
Audio quality
Automotive original equipment manufacturers (OEMs) increasingly demand higher audio quality to provide a tailored user experience that enhances brand recognition and affinity.
Audio quality specs depend on the amplifier’s total harmonic distortion (THD) and the signal chain’s signal-to-noise ratio (SNR) and dynamic range (DR).
Reliability
Automotive applications are known to demand higher levels of reliability compared to personal electronics applications; AEC-Q100-qualified devices offer a high level of reliability tailored for automotive applications.
In addition, Q100-qualified audio amplifiers with integrated diagnostics and protection take reliability to an even higher level. For example, audio amplifiers with integrated diagnostics can signal to an external microprocessor whether the speaker has been disconnected or has its terminals shorted to each other, to ground or to its voltage rail.
Integrated diagnostics are particularly important during car assembly to ensure that the sound system has been properly installed and that no shorts occurred during speaker installation. Also, this feature can help ensure that safety-related systems, like instrument clusters and other telematics that alert users of out-of-the-ordinary conditions, are continuously operational.
Cost
Much has been said about how Class-AB audio amplifiers are more cost-effective than their Class-D counterparts. When considering the IC by itself this may be true; but system designers must consider the cost of the whole audio solution.
For example, the fundamental differences in efficiency between Class-AB and Class-D audio amplifiers has an impact on the audio solution cost. The lower-efficiency Class-AB amplifier requires more complex and expensive thermal management. Expensive heatsinks and an additional printed circuit board (PCB) area for thermal dissipation are very common downsides to using Class-AB amplifiers.
To be fair, Class-D amplifiers require an external inductor that adds some cost to the solution, but with recently released automotive-grade, low-cost inductors, Class-D amplifier inductor cost can be minimized. With this in mind – and with instrument clusters being a very space-constrained application – Class-AB amplifiers are no longer the preferred audio solution, as Class-D amplifiers offer higher system performance at a comparable total solution cost.
The TAS5421-Q1 is designed for these applications. As a Class-D amplifier, it minimizes solution size while simplifying thermal management. Its fully integrated diagnostics and protection capabilities reduce bill-of-materials (BOM) cost and (most importantly) enhance system reliability. The TAS5421-Q1 is also compliant to the CISPR 25-L5 automotive electromagnetic interference (EMI) specification.
A higher-voltage Class-D audio amplifier, like TAS5421-Q1, is not the only topology used in instrument clusters. Other possible topologies include discrete protection/diagnostics and the use of step-up and/or step-down converters. I’ll discuss these topologies in greater detail in a future blog post, so be sure to subscribe to the Behind the Wheel blog to stay in the loop.
Additional resources:
- Keep in mind other TI audio devices for an instrument cluster, like the TAS5421-Q1 or TLV320DAC3100-Q1.
- Explore other TI devices suitable for instrument cluster applications in this system block diagram.
- Use this audio selection tool to narrow the search for the right audio amplifier for your needs.
- Join the TI E2E Audio Community to search for solutions and share knowledge with fellow engineers and TI experts.
