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

3.2.2 Class-H Configuration Settings

The Configuration Window in Figure 3-2 provides the following options:

  1. TAS278x Class-H Controls
    • IOVDD Voltage: Default = 1.8 V
    • Hybrid-Pro Feedback (HPFB) PWM steps
      Table 3-1 HPFB PWM Steps Configuration
      Options Description Comments
      16 steps 0 V to IOVDD voltage divided into 16 steps with 192-kHz control frequency Provides smoother control signal at the FB pin of boost converter
      8 steps 0 V to IOVDD voltage divided into 8 steps with 384-kHz control frequency Requires higher cutoff frequency for the external LPF than that used for 16 steps, 192-kHz setting
    • Open-Drain or Push-Pull: The PWR_CTRL pin can be configured in either open-drain or push-pull output. When two devices drive the same external resistive network of the boost converter, the open-drain output is needed. Push-pull gives better efficiency but can be used only with one device associated with a boost converter. When only one TAS278x device is controlling the boost converter, select the push-pull output by deselecting the open-drain checkbox. Check the Open-drain box to interface multiple TAS278x devices to the boost converter.
  2. Boost Converter Configuration

    Table 3-2 shows the configuration options for the boost converter.

    Table 3-2 Boost Converter Options
    Option Description
    Min Voltage Expected boost minimum output voltage
    Max Voltage Expected boost maximum output voltage
    FB Reference Voltage FB reference voltage of the boost converter, which is normally listed in the data sheet
    R1 Resistance Boost FB pullup resistor value, used to calculate the pulldown resistor on the FB pin (R2) as well as the LPF (R3, C1, R4, C2) (refer to Figure 3-2)
    Boost Interface Overview This section shows the hardware circuit connections between TAS278x and boost converter as the recommended circuit for the Hybrid-Pro control application design. The section includes second-order LPF and matching resistor values. These values are calculated based on inputs provided in the configuration window.
    TAS278x Output Voltage versus Boost Voltage PPC3 suite plots the audio output amplitude versus boost output voltage for the TAS278x and boost system settings.
  3. Envelope Tracking Algorithm

    Figure 3-3 shows the advanced Hybrid-Pro controls. These controls, available for the envelope tracking algorithm, are described in Table 3-3.

    Table 3-3 Envelope Tracking
    Option Description
    Lookahead Time TAS278x has maximum 4-ms delay buffer that can be configured based on response of various boost converters for low-distortion
    Margin Class-H margin can be used to add output margin for low distortion by internally fine tuning the threshold and steps. The trade-off is that higher margin results in lower battery life.
    Class-H Threshold and Step-Size PPC3 automatically calculates the class-H threshold and step size based on the system configuration
    Inflation Factor This control is used to artificially inflate the input to correct for any mismatch between the envelope tracking estimate and the class-D output
    Peak Hold Time When the audio signal starts falling, the tracker holds the peak for a certain duration to prevent rapid voltage fluctuations. This needs to be larger than the lookahead time. The default setting is 8 ms.
    Smooth This is the alpha coefficient for the smoothing filter on the audio envelope. The default setting is 24 samples or 0.5 ms at 48 kSPS.
    Peak Decay The class-H controller peak voltage follows the falling audio signal using a decay envelope to enable the boost converter to switch to a lower headroom. The default peak decay is set at –0.4455 dB per sample.

    Disable the supply tracking limiter of TAS278x or program the thresholds to a value higher than the maximum output voltage of the boost converter when using the external boost controller.

Figure 3-2 Class-H Controls in Device Control Page
Figure 3-3 Class-H Advanced Controls

Refer to the PAGE 0x05 and PAGE 0x06 registers from the register map of the TAS278x data sheet for details on programming the internal class-H controller.