4 Summary

LC filter design is critical for automotive class-D audio amplifier. Select the LC filter configuration according to the switching frequency, power system, thermal, audio performance, and the end-system EMC specifications. From the results of the LC filter configuration with different inductors study, it is clear that the inductor plays a large role in the audio performance. The inductance value, DCR, and linearity factor into the total system performance and must be considered based on the design goals of a specific application.

For the TAS6x84-Q1 family of devices, the fourth-order filter configuration 10μH / 1μF + 1μH / 0.22μF is standard configuration for better audio performance due to the reduced ripple current with higher inductance. From the TAS6584-Q1 device test data, the audio performance of 10μH / 1μF + 1μH / 0.22μF LC filter is better than
10μH + 2.2μF configuration with same 10μH part number inductor.

DCR also must be considered on high-output power applications. Although a 10μH / 1μF + 1μH / 0.22μF configuration can show improved power dissipation for low output power due to reduced ripple current, if the application has high DCR, the losses can be greater at high currents than a 10μH + 2.2μF configuration with higher ripple current. From the test data of TAS6584-Q1 device, the output power capacity with the inductor which has lower DCR is higher than the inductor which has higher DCR at same LC filter configuration. And the inductor which has lower DCR also has better THD + N performance on high output power.

With different impedance loads, some LC filter configurations can make frequency response seriously overdamped or seriously underdamped at high frequency. Besides LC filter adjustment, tuning TAS6x84-Q1 family internal gain compensation biquads helps achieve a flat frequency response. Appendix A introduces the detailed tuning guide.

Detail ratings and specifications of inductance value, handling current and linearity can be obtained through inductor manufacturers. Actual inductance value with current increase greatly affects audio performance. Higher inductance value gets better audio performance. Evaluate the size and price of the inductors before making the final selection. Although the price of the inductors has not been part of this study, typically, the smaller the inductor, the lower the cost.