Digital audio power amp simplifies infotainment system design

December 21, 2015 // By Christoph Hammerschmidt
STMicroelectronics (ST) has launched the second generation of power amplifiers for car audio applications. The new FDA801 and FDA801B 4-channel class-D amplifiers with digital input convert the digital audio source directly into high-quality, cabin-filling sound.

The digital input gives immunity to interference noise from mobile radio, improves sound quality, saves component costs, and simplifies system design. The product represents ST’s second generation class-D digital-input automotive-audio amplifiers. A range of pin-compatible products in various configurations will be available soon, ST announced.

The new power amplifiers combine high audio quality and increased energy efficiency, as well as the real-time measurement of speaker impedance via the new Digital Impedance Meter (FDA801B) – a unique feature that represents a quantum leap in automotive diagnostics compared to other available amplifiers.

In addition to simplifying circuit design, the digital input and external feedback topology make the amplifier’s frequency response independent of the load impedance and output-filter design. This allows scaling to create multiple product variants based on a common platform, without requiring detailed redesign of the amplifier. Unlike analogue-input class-D amplifiers, the FDA801/B can be used in head units as well as booster amps thanks to superior noise immunity, lower switching interference, and lower power dissipation that permits smaller heatsinks.

Key to these enhancements is ST’s fabrication process, BCD9s, which minimizes interference between circuits on the chip, lowers standby-power consumption, and cuts power-transistor dissipation raising efficiency to more than 93%.

By dissipating less power, the FDA801/B can help boost fuel economy in conventional vehicles and extend the driving range of hybrids or battery EVs. Like their predecessors, ST’s new amplifiers are compatible with fuel-saving start-stop technology, maintaining uninterrupted playback when the vehicle battery voltage dips as the engine is restarted.

Key Technical Features include:

  • 115dB Signal to Noise Ratio (SNR); 110dB dynamic range
  • Simplified digital input eliminates external DAC (Digital to Analog Converter) and external decoupling capacitor, thereby avoiding potential DC-offset problems
  • More than 40% power saving compared to standard class-D amplifiers
  • Digital Impedance Meter (DIM, in FDA801B) automatically recognizes magnitude and phase of the connected speaker and communicates it by digital bus (I2C)
  • Internal 24-bit DAC conversion and very low