They are almost identical, both offering a digital (I2S) front end, digital core, 24bit DAC (100dB resolution), a Class-D trans-resistance PWM output stage and internal feedback before the required external LC output filter.
“Thanks to interpolation and noise-shaping, the digital signal processing allows to reach up a good audio performance in a small device area,” said ST. “The internal PLL uses the clock frequency of the bit stream to generate the internal clock for the digital part and PWM for the outputs.”
Sampling rates between 8 and 96kHz can be selected, where lower rates consume less memory space when storing warning tones.
Configuration is though a I2C bus, and in-play diagnostics includes clipping detection, thermal warning, over-current protection and open-load detection.
Of the two, FDA903S (the other is FDA803S) has real-time load current monitoring through a digital admittance meter, with the intention of introducing functional safety grade self-diagnostics towards ASIL-A certification.
Both devices come in 5 x 5mm QFN32 exposed pad packages that dump heat into the PCB and are intended to work without an additional heatsink.
EVAL-FDA903S is the associated evaluation board.
The combined FDA803S FDA903S product page can be found here. Data briefs are available but, as it becoming common with complex automotive parts, full data sheets are not openly available.
