SLOS814D March 2014 – September 2016 TAS5421-Q1
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
The device is a mono high-efficiency class-D audio amplifier. Typical use of the device is to amplify an audio input to drive a speaker. The intent of its use is for a bridge-tied load (BTL) application, not for support of single-ended configuration. This section presents how to use the device in the application, including what external components are necessary and how to connect unused pins.
Use the following for the design requirements:
The device requires only a single power supply compliant with the recommended operation range. The device is designed to work with either a vehicle battery or regulated power supply such as from a backup battery.
The device communicates with the system controller with both discrete hardware control pins and with I2C. The device is an I2C slave and thus requires a master. If a master I2C-compliant device is not present in the system, the device can still be used, but only with the default settings. Diagnostic information is limited to the discrete reporting FAULT pin.
Table 9 lists the components required for the device.
|EVM DESIGNATOR||QUANITY||VALUE||SIZE||DESCRIPTION||USE IN APPLICATION|
|C7||1||10 μF ± 10%||1206||X7R ceramic capacitor, 25-V||Power supply|
|C8||1||330 μF ± 20%||10 mm||Low-ESR aluminum capacitor, 25-V||Power supply|
|C9, C16, C20||3||1 μF ± 10%||0805||X7R ceramic capacitor, 25-V||Analog audio input filter, bypass|
|C10, C14||2||0.22 μF ± 10%||0603||X7R ceramic capacitor, 25-V||Bootstrap capacitors|
|C11, C17||2||3.3 μF ± 10%||0805||X7R ceramic capacitor, 25-V||Amplifier output filtering|
|C13, C15||2||470 pF ± 10%||0603||X7R ceramic capacitor, 250-V||Amplifier output snubbers|
|C6||1||0.1 μF ± 10%||0603||X7R ceramic capacitor, 25-V||Power supply|
|C2||1||2200 pF ± 10%||0603||X7R ceramic capacitor, 50-V||Power supply|
|C3||1||0.082 μF ± 10%||0603||X7R ceramic capacitor, 25-V||Power supply|
|C4, C5||2||4.7 μF ± 10%||1206||X7R ceramic capacitor, 25-V||Power supply|
|C12, C18||2||0.01 μF ± 10%||0603||X7R ceramic capacitor, 25-V||Output EMI filtering|
|L1||1||10 μH ± 20%||13.5 mm ×13.5 mm||Shielded ferrite inductor||Power supply|
|L2||1||22 μH ± 20%||8 mm × 8 mm||Coupled inductor||Amplifier output filtering|
|R5, R6||2||49.9 kΩ ± 1%||0805||Resistors, 0.125-W||Analog audio input filter|
|R4, R7||2||5.6 Ω ± 5%||0805||Resistors, 0.125-W||Output snubbers|
Output FETs drive the amplifier outputs in an H-bridge configuration. These transistors are either fully off or 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 low-pass filter to filter out the PWM modulation carrier frequency. People frequently call this filter the L-C filter, due to the presence of an inductive element L and a capacitive element C to make up the 2-pole low-pass filter. The L-C filter attenuates the carrier frequency, reducing electromagnetic emissions and smoothing the current waveform which the load draws from the power supply. See Class-D LC Filter Design for a detailed description on proper component selection and design of an L-C filter based upon the desired load and response.
A snubber is an RC network placed at the output of the amplifier to dampen ringing or overshoot on the PWM output waveform. Overshoot and ringing has several negative impacts including: potential EMI sources, degraded audio performance, and overvoltage stress of the output FETs or board components. For more information on the use and design of output snubbers, see Class-D Output Snubber Design Guide.
The output stage uses dual NMOS transistors; therefore, the circuit requires bootstrap capacitors for the high side of each output to turn on correctly. The required capacitor connection is from BSTN to OUTN and from BSTP to OUTP as shown in Figure 17.
The circuit requires an input capacitor to allow biasing of the amplifier put to the proper dc level. The input capacitor and the input impedance of the amplifier form a high-pass filter with a –3-dB corner frequency determined by the equation: f = 1 / (2πR(i)C(i)), where R(i) is the input impedance of the device based on the gain setting and C(i) is the input capacitor value. Table 10 lists largest recommended input capacitor values. Use a capacitor which matches the application requirement for the lowest frequency but does not exceed the values listed.
|GAIN (dB)||TYPICAL INPUT IMPEDANCE (kΩ)||INPUT CAPACITANCE (µF)||HIGH-PASS FILTER (Hz)|
Use the following steps for the design procedure:
For questions and support, go to the E2E forums.
Even if unused, always connect pins to a fixed rail; do not leave them floating. Floating input pins represent an ESD risk, therefore the user must adhere to the following guidance for each pin.
If the MUTE pin is unused in the application, connect it to GND through a high-impedance resistor.
If the STANDBY pin is unused in the application, connect it to a low-voltage rail such as 3.3 V or 5 V through a high-impedance resistor.
If there is no microcontroller in the system, use of the device without I2C communication is possible. In this situation, connect the SDA and SCL pins to 3.3 V.
If the FAULT pin does not report to a system microcontroller in the application, connect it to GND.
When using a single-ended audio source, ac-ground the negative input through a capacitor equal in value to the input capacitor on the positive input, and apply the audio source to the positive input. For best performance, the ac ground should be at the audio source instead of at the device input if possible.
See the Typical Characteristics section for application performance plots.