SLOA326 October   2022 TAS2781

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Hybrid-Pro Boost Controller
  5. 3Hardware, Software, and Test Results
    1. 3.1 Hardware Connections
      1. 3.1.1 Schematic Connections
      2. 3.1.2 Equations
    2. 3.2 Software Settings
      1. 3.2.1 Steps To Enable Class-H Using PPC3
      2. 3.2.2 Class-H Configuration Settings
    3. 3.3 Hybrid-Pro Feature Performance Results
      1. 3.3.1 Class-H Operation
        1. 3.3.1.1 PWM Steps
        2. 3.3.1.2 Lookahead Time
        3. 3.3.1.3 Margin
        4. 3.3.1.4 Inflation Factor
      2. 3.3.2 Battery Life
      3. 3.3.3 Thermal Performance
  6. 4References

1 Introduction

Traditional audio amplifier systems consist of an audio amplifier and a boost converter with a constant output voltage to achieve the maximum power to be delivered to the speaker load.

Modern audio amplifiers with class-D architecture provide efficiencies higher than 90%. Higher efficiency results in lower power consumption and longer battery-life. This allows class-D amplifiers to be used for compact system designs across various applications like home theater, portable speaker, soundbar, car-audio, and so forth.

The dynamic nature of music, typically, needs maximum voltage for short moments, and only when the listener sets the system to maximum volume. Hence a fixed-voltage power supply is inefficient in most use cases due to larger inductors, MOSFETs, and copper area on the PCB to handle the increased thermal load. These system challenges can be solved with an envelope-tracking power-supply system. The audio signal is analyzed to determine the optimum power supply voltage for a given audio input. The power-supply voltage is adjusted by dynamically controlling the output voltage of the boost converter. The entire system operates to directly match the needs of the audio signal at all times instead of only maintaining the voltage required at the maximum power use-case. Power losses in the system are reduced and power efficiency and thermals improve significantly.

GUID-20221019-SS0I-BNHR-LZ72-D8QNN7JMKG5T-low.png Figure 1-1 Envelope Tracking

In a class-G system, the supply voltage for the class–D output is boosted when needed. The audio amplifier is able to monitor the input audio stream and determine the corresponding optimum output voltage for the amplifier. If the output voltage exceeds a certain threshold then the boost is enabled to provide additional headroom. In class-H amplifiers, the output voltage level of the boost converter for the amplifier has a more granular level. With this implementation there can be several possible supply voltages as shown in Figure 1-3. This enables the output to operate with just enough headroom to maintain low distortion while achieving higher output efficiency.

Figure 1-2 Class-G Profile
Figure 1-3 Class-H Profile

The integrated class-H controller, usually known as the Hybrid-Pro boost controller, of the TAS2781 and TAS2783 can track the envelope of the incoming audio stream and control the boost converter to adjust the power supply voltage for the audio amplifier. This envelope tracking algorithm looks ahead into the audio signal to detect a peak and prepare the boost converter to switch to a higher supply voltage. The Hybrid-Pro boost controller sends out a pulse-width modulation (PWM) signal, with duty cycle proportional to the peak, to the boost converter. The output from the audio amplifier has a programmable delay to allow the boost converter to settle to the voltage level. When the audio signal starts falling, the tracker holds the peak for a certain duration to prevent rapid voltage fluctuations. Finally, the Hybrid-Pro boost controller follows the falling audio signal using a decay envelope to enable the boost converter to switch to a lower headroom. Monitoring of the audio signal or external control of the boost converter from a microcontroller is not necessary.