SDAA313A March   2026  – May 2026 INA1650-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Automotive Hi-Fi Headphone Audio System Overview
    1. 2.1 Key Technical Specifications of Automotive Hi-Fi Audio Systems
    2. 2.2 Design Requirements for Automotive Hi-Fi Headphone Audio Systems
  6. 3Automotive Hi-Fi Headphone Audio System Working Principle and Circuit Design
    1. 3.1 DAC Circuit Design
    2. 3.2 Differential-to-Single-Ended Circuit Design
  7. 4Simulation
    1. 4.1 Transient Response Simulation
    2. 4.2 Noise Analysis
    3. 4.3 Power Consumption Simulation and Thermal Calculation
  8. 5Experimental Test
  9. 6Summary
  10. 7References
  11. 8Revision History

2.2 Design Requirements for Automotive Hi-Fi Headphone Audio Systems

For automotive applications, the design requirements of the Hi-Fi headphone audio system are specified as follows:

Table 2-1 Design Targets
Supply Voltage <12v
THD+N (1kHz/32 Ω) <0.001%
Maximum Output Power 100mW

To verify sufficient volume for low-sensitivity headphones, a headphone amplifier is required to deliver significant output power across a full range of load conditions. This poses a design challenge: delivering a specific power to a high-impedance headphone load demands a higher amplifier output voltage (and thus a higher supply voltage), while delivering the same power to a low-impedance headphone requires a considerably higher amplifier output current.

Output Power Limitations

The output power of an operational amplifier (op amp) is constrained by multiple factors. For high-impedance loads, the slew rate and full-power bandwidth of the op amp are the primary limiting factors. The full power bandwidth is the frequency range over which the op amp can deliver maximum output power without significant distortion. For low-impedance loads, the output current limit of the op amp becomes the dominant constraint. Additionally, the current limit is subject to thermal effects: high power dissipation inside the op amp causes a rise in its junction temperature, which in turn reduces the current limit and consequently increases audio distortion.

This issue is particularly pronounced when driving low-impedance loads with a relatively high supply voltage, as the high output current required by low-impedance loads leads to rapid excessive power dissipation, which significantly restricts the available output power.

Output Power Enhancement

The power delivered to low-impedance headphones can be increased by using a lower supply voltage, which reduces the power dissipation of the op amp. However, this may not be a viable design in some applications, as a reduced supply voltage will significantly degrade the power delivery to high-impedance headphones. Selecting an op amp with automotive higher power rating can mitigate the impact of power dissipation, yet many applications benefit substantially from the superior performance of low-power op amps such as the INA1650-Q1. In such cases, paralleling two channels of the op amp can deliver the required output power.

The power requirement of most general consumer-grade headphones ranges from 10 mW to 100 mW, a range that meets the daily listening needs of most users. This design is optimized for a maximum power requirement of 100 mW, a value sufficient to drive a wide range of headphone models. A headphone impedance RHP of 32 Ω is selected for the design, as this is a standard impedance value for portable audio headphones. Therefore, the required output voltage for a 32 Ω headphone can be calculated as follows:

Equation 4. V o = P I N × R H P = 100 m W × 32 = 1.789 V R M S