117dB audio amplifier uses Class-G output stage
Author: EIS Release Date: Apr 27, 2022
STMicroelectronics is using Class-G analogue audio technology to create 117dB S/N ratio, >117dB dynamic range (A-weighted), automotive amplifier.
Class-G amplifiers are similar to traditional Class-AB amplifiers except that, to increase electrical efficiency, the output devices are supplied from a low voltage rail when output signals are small, and a higher voltage rail during loud passages.
In this case, an integrated buck controller automatically varies the rail voltage depending on the audio-signal level, resulting in “smooth, analogue sound with near-class-D efficiency at normal listening levels,” according to the company. “Because the power dissipation is much lower compared with a conventional Class-AB amplifier, the heatsink requirement is optimised.”
Four loudspeaker-driving mosfet bridge-tied load audio output amplifiers are included in the part, called TDA7901 (see diagram): 4 x 43W of “audio power”, said ST, with 4Ω loads and the outputs saturated at 14.4V.
THe data brief (there is no public data sheet) quotes 4 x 27W into 4Ω (14.4V 1kHz 10%THD) and 4 x 47W 2Ω (14.4V 1kHz 10%THD)
Bandwidth is 80kHz and the supply can vary across 4.5 – 18.5V.
While the outputs are analogue, inputs are digital I2S, with a programmable PLL that can at 64x sample rate for all input configurations. Audio is 24bit.
As the devices is for automotive use and the company is proposing it for in-vehicle information systems and smart cockpits, which could include warning-tone generators and AVAS (acoustic vehicle alerting systems) diagnostics including a digital load impedance meter and real-time load-current monitoring through I2C is included towards ASIL-A safety certification. The same bus can be used to configure the IC.
“TDA7901 guarantees EMI performance in line with the CISPR25-restrictive standard requirement,” added ST. AEC-Q100 qualification is “ongoing”.
Packaging is power-SO36, with 1°C/W max junction-to-case thermal resistance, and production is scheduled for the second half of this year.