SLAA898 September   2022 TAS3251 , TPA3255

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
    1. 1.1 Power Amplifiers
    2. 1.2 Discrete Power Amplifier Implementation
    3. 1.3 Class-D Amplifier Implementation
    4. 1.4 Advantage of a Class-D Implementation
  4. 2Background
    1. 2.1 Why Use Constant Voltage Audio Systems
    2. 2.2 Basic Principle of Constant Voltage Systems
    3. 2.3 Power Loss in Transformer
    4. 2.4 Auto-Transformer
  5. 3System Test (Based on TPA3255)
    1. 3.1 Transformer Characteristics
      1. 3.1.1 Turns Ratio and Resistance Match
      2. 3.1.2 DCR of the Transformer
    2. 3.2 System Build-Up
    3. 3.3 System Test
  6. 4Efficiency Analysis and Optimization
    1. 4.1 Efficiency of Three Parts
      1. 4.1.1 Efficiency for TPA3255
      2. 4.1.2 Efficiency for Step-Up Transformer
      3. 4.1.3 Efficiency for Step-Down Transformer 330-040
    2. 4.2 Improvements on System Efficiency
      1. 4.2.1 Improve Resistance Matching
      2. 4.2.2 Apply a Transformer With Less Power Loss
  7. 5Considerations on Building a Constant Voltage System
    1. 5.1 Transformer Saturation
    2. 5.2 Low DCR
    3. 5.3 Resistance Matching

1.3 Class-D Amplifier Implementation

Figure 1-2 shows a more simple and integrated implementation of the power amplifier.

Figure 1-2 Power Amplifier Implementation With an Integrated Class-D Amplifier

In the integrated Class-D amplifier design, most of the discrete signal conditioning circuitry is removed and moved onto a single chip. This greatly simplifies the signal chain and overall circuit complexity. As with the discrete implementation, the transceiver at the beginning of the signal chain allows for communication between the power amplifier and central control unit. Then, the digital processing block determines which signal to send to the Class-D amplifier. Depending on the Class-D amplifier, the input can be either analog or digital, denoted by the TPA and TAS prefixes, respectively. The TPA3255 is an example of an analog input Class-D amplifier, and the TAS3251 device is an example of a digital input Class-D amplifier. The output of the Class-D amplifier then goes through the audio transformer and is distributed to the NACs.

The integrated Class-D amplifier implementation of the power amplifier still requires some of the same power blocks as the discrete implementation. The DC/DC boost, instead of being applied to the output driver FETS in the discrete circuit, is supplied directly to the Class-D amplifier. The Class-D amplifier then uses this voltage for the same purpose of providing the output amplitude of the power amplifier. The DC/DC buck is used for the main power supply of the Class-D amplifier. Finally, the LDOs serve two different functions: one is for the power supply of the microcontroller unit (MCU) and the other is for the internal digital circuitry of the Class-D amplifier.