Introduction
The STA538 is a digital stereo class-D audio amplifier. It includes an audio DSP, a ST proprietary high-efficiency class-D driver and CMOS power output stage. It is intended for high-efficiency digital-to-power-audio conversion for portable applications. The STA538 also provides output capabilities for FFXTM. In conjunction with a power device, the STA538 provides high-quality digital amplification.

FEATUREs
■ Up to 96 dB dynamic range
■ Sample rates from 8 kHz to 192 kHz
■ FFXTM class-D driver
■ 1.5 V to 1.95 V digital power supply
■ 1.5 V to 3.6 V analog power supply
■ 18-bit audio processing and class-D FFXTM modulator
■ Digital volume control:
   – +36 dB to 105 dB in 0.5 dB steps
   – Software volume update
■ Individual channel and master gain/attenuation
■ Automatic invalid input detect mute
■ 2-channel I2S input/output data interface
■ Digitally controlled POP-free operation
■ Input and output channel mapping
■ 250 mΩ output CMOS Rdson
■ > 90% efficiency
■ 2 x 1.3 W (10% THD) on 4 Ω at 3.6 V
■ 2 x 0.7 W (10% THD) on 8 Ω at 3.3 V
■ Stereo headphone plus mono speaker application:
   – 50 mW stereo into 32 Ω headphone, 1.2 W mono into 4 Ω speaker at 3.3 V
   – 100 mW stereo into 16 Ω headphone, 1.2 W mono into 4 Ω speaker at 3.3 V