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Class G amplifier targets compact and high definition car audio

The TDA7901 amplifier developed by STMicroelectronics implements a Class G audio mode of operation. The Class G topology is to play both ways. This is a power supply modification that takes advantage of the fact that music and voice signals have a high crest factor, with most of the signal content being at lower amplitudes. Crest factor, sometimes called peak-to-average ratio, is the difference in decibels between the peak and average levels of a signal.

Here, Class G works based on an integrated step-down controller that automatically adjusts the voltage rail according to the level of the audio signal. Thus, efficiency is optimized at each output level. According to ST, the TDA7901 is nearly as efficient as a Class-D amplifier when delivering the normal listening level of audio power (1W).

Due to its Class G approach, the “output power” dissipated under average listening conditions can be reduced more than in standard Class AB devices. Power dissipation is much lower than that of a typical Class AB amplifier; therefore, the heat sink requirement is also optimized.

The TDA7901 is a single-chip quad-bridge amplifier that incorporates a full-featured digital-to-analog converter (DAC), digital input for direct connection to I2S and MOSFET output stages. Integrating the buck controller into the IC helps reduce system size and weight, reduces material BOM, simplifies circuit design, and avoids developing firmware to control the voltage rail.

Applications and Specifications

The new amplifier is suitable for many in-car infotainment systems (IVI), such as head units, smart cockpit systems, external amplifiers, etc. It features comprehensive in-game diagnostics, including real-time charging current monitoring via I2S or I2C interfaces, enabling ASIL-A certification of safety-related applications such as warning tone generators and acoustic vehicle alert systems. A digital impedance meter is also provided, ensuring that systems containing the TDA7901 can meet the demanding requirements of automotive OEMs.

Numbers aren’t everything, but the part, which also provides immunity to any input disturbance, helps deliver audio performance that reaches 117dB S/N ratio with over 117dB of dynamic range and a low noise. In addition, it offers a flat frequency response up to 80 kHz and supports HD (high definition) audio.

With his I2Digital S input and quad-bridge-tied-load (BTL) output, the TDA7901 delivers 4x 43W of audio power (at 4Ω load and outputs saturated at 14.4V, according to ST). The amplifier’s wide supply voltage range, extending from 4.5 to 18.5 V, prevents disturbances caused by start-stop motor operation and general automotive electrical transients. Car manufacturers have adopted the “start-stop” function as a means of reducing fuel consumption.

A diagnostic board communicates the status of each loudspeaker via the I2Bus C. A digital impedance meter (DIM) function measures the value of the load. The same me2The C-Bus allows the part to control multiple device configurations.

Meet multiple requirements

STMicroelectronics emphasizes that the TDA7901 guarantees EMI performance that meets the requirement of the restrictive CISPR 25 standard. CISPR is responsible for developing and maintaining the standards used to measure the emissions produced by vehicles and their components. CISPR 25 deals with “Radio disturbance characteristics for the protection of receivers used in vehicles”.

To meet environmental requirements, ST offers these devices in different qualities of ECOPACK packaging, depending on their level of environmental compliance. ST products are classified according to the following ECOPACK grades (ECOPACK is an ST brand):

  • ECOPACK or ECOPACK1: Compliant with the RoHS directive, have a lead-free second level interconnection (with a reliability suitable for soldering at higher temperatures) and comply with the ELV directive.
  • ECOPACK2: ECOPACK1 + free of brominated, chlorinated and antimony flame retardants.
  • ECOPACK3: ECOPACK2+ halogen-free without RoHS derogations.

The TDA7901 is expected to enter production in the second half of 2022, in a Power-SO36 package that helps reduce overall system space occupancy and cost. Pricing starts at $7.90 for orders of 1,000 pieces.