TPA3110D2-Q1

SLOS794B – SEPTEMBER 2012 – REVISED SEPTEMBER 2015

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Typical Application (continued)

8.2.2 Detailed Design Procedure

8.2.2.1 TPA3110D2-Q1 Modulation Scheme

The TPA3110D2-Q1 uses a modulation scheme that allows operation without the classic LC reconstruction filter

when the amp is driving an inductive load. Each output is switching from 0 volts to the supply voltage. The OUTP

and OUTN are in phase with each other with no input so that there is little or no current in the speaker. The duty

cycle of OUTP is greater than 50% and OUTN is less than 50% for positive output voltages. The duty cycle of

OUTP is less than 50% and OUTN is greater than 50% for negative output voltages. The voltage across the load

in the load.

See Figure 42 for a plot of the output waveforms.

8.2.2.2 Ferrite Bead Filter Considerations

Using the advanced emissions suppression technology in the TPA3110D2-Q1 amplifier, it is possible to design a

high efficiency Class-D audio amplifier while minimizing interference to surrounding circuits. It is also possible to

accomplish this with only a low-cost ferrite bead filter. In this case it is necessary to carefully select the ferrite

bead used in the filter.

One important aspect of the ferrite bead selection is the type of material used in the ferrite bead. Not all ferrite

material is alike, so it is important to select a material that is effective in the 10- to 100-MHz range which is key to

the operation of the Class-D amplifier. Many of the specifications regulating consumer electronics have

emissions limits as low as 30 MHz. It is important to use the ferrite bead filter to block radiation in the 30-MHz

and above range from appearing on the speaker wires and the power supply lines which are good antennas for

these signals. The impedance of the ferrite bead can be used along with a small capacitor with a value in the

range of 1000 pF to reduce the frequency spectrum of the signal to an acceptable level. For best performance,

the resonant frequency of the ferrite bead and capacitor filter should be less than 10 MHz.

Also, it is important that the ferrite bead is large enough to maintain its impedance at the peak currents expected

for the amplifier. Some ferrite bead manufacturers specify the bead impedance at a variety of current levels. In

this case it is possible to make sure the ferrite bead maintains an adequate amount of impedance at the peak

current the amplifier sees. If these specifications are not available, it is also possible to estimate the bead current

handling capability by measuring the resonant frequency of the filter output at low power and at maximum power.

A change of resonant frequency of less than fifty percent under this condition is desirable. Examples of tested

ferrite beads that work well with the TPA3110D2-Q1 include 28L0138-80R-10 and HI1812V101R-10 from

Steward and the 742792510 from Wurth Electronics.

A high quality ceramic capacitor is also needed for the ferrite bead filter. A low ESR capacitor with good

temperature and voltage characteristics works best.

Additional EMC improvements may be obtained by adding snubber networks from each of the Class-D outputs to

ground. Suggested values for a simple RC series snubber network would be 10

Ω in series with a 330-pF

capacitor although design of the snubber network is specific to every application and must be designed taking

into account the parasitic reactance of the printed circuit board as well as the audio amp. Take care to evaluate

the stress on the component in the snubber network especially if the amp is running at high PVCC. Also, make

sure the layout of the snubber network is tight and returns directly to the PGND or the PowerPAD™ integrated

circuit package beneath the chip.

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