SLOS970B January 2018 – January 2025 TPA6404-Q1
PRODUCTION DATA
Refer to the PDF data sheet for device specific package drawings
The output FETs drive the amplifier outputs in an H-Bridge configuration. These transistors are either fully off or fully on. The result is a square-wave output signal with a duty cycle that is proportional to the amplitude of the audio signal. The amplifier outputs require a reconstruction filter that comprises a series inductor and a capacitor to ground on each output, generally called an LC filter. The LC filter attenuates the PWM frequency and reduces electromagnetic emissions, allowing the reconstructed audio signal to pass to the speakers. refer to the Class-D LC Filter Design, SLAA701A, application report for a detailed description of proper component description and design of the LC filter based upon the specified load and frequency response.
The recommended low-pass cutoff frequency of the LC filter is dependent on the selected switching frequency. The low-pass cutoff frequency can be as high as 100kHz for a PWM frequency of 2.1MHz.
Certain specifications must be understood for a proper inductor. See the application note TAS6424-Q1 Inductor Selection Guide, SLOA242, for information on selection the proper inductor. The inductance value is given at zero current, but the inductors will have current through them as the TPA6404-Q1 drives current into the load. Use the inductance versus current curve for the inductor to made sure the inductance does not drop below 2uH (for fsw = 2.1MHz) at the maximum current for the system design during normal operation. The DCR of the inductor directly affects the output power of the system design. The lower the DCR, the more power is provided to the speakers. The typical inductor DCR for a 4Ω system is 40 to 50mΩ and for a 2Ω system is 15 to 25mΩ.