Conventional class-D audio amplifiers operate the PWM output section open-loop, which makes the amplifier susceptible to power-supply variations. Even advanced class-D amplifiers will have an only -40-dB spec on PSRR at 60 Hz. The Freescale FSA95601 uses an innovative digital feedback technique to achieve remarkable performance. It achieves THD (total harmonic distortion) of -120 dB and IMD (intermodulation distortion) of -110 dB. Open-loop systems require very fast transitions at the output of the switching power stage to achieve reasonable distortion performance. Fast switching transitions are detrimental to EMI performance. The Freescale FSA95601 allows for slower transitions at the switching-power-stage output. Overall, this chip set represents a significant advancement in system-level class-D audio amplifiers.

Due to its immunity to power-supply variations, the first application for this chip set is in the automotive industry. The chips target applications requiring 50 to 100W (bridged) per channel. In addition, the chip set offers advanced protection features such as undervoltage, overvoltage, and overtemperature warning, and it provides advanced turn-on/off audio click and pop suppression. The FSA95601 includes around 100 MIPS of 24-bit-word-length digital signal processing per channel. The digital-domain conversion technique from pulse-code-modulation input signals to the digital pulse-width-modulation output signals is patented. In fact, the government has granted the chip set nine patents so far, and another three patents are pending.