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PRINTED-CIRCUIT BOARD (PCB) LAYOUT GENERAL GUIDELINES

BASIC MEASUREMENT SYSTEM

TPA3107D2

SLOS509A – OCTOBER 2006 – REVISED NOVEMBER 2006

Because the TPA3107D2 is a class-D amplifier that switches at a high frequency, the layout of the printed-circuit

board (PCB) should be optimized according to the following guidelines for the best possible performance.

•

Decoupling capacitors—The high-frequency 1-

µF decoupling capacitors should be placed as close to the

PVCC and AVCC terminals as possible. The VBYP capacitor, VREG capacitor, and VCLAMP capacitor

should also be placed as close to the device as possible. Large bulk power supply decoupling capacitors

should be placed near the TPA3107D2 on the PVCCL, PVCCR, and AVCC terminals.

•

Grounding—The AVCC decoupling capacitor, VREG capacitor, VBYP capacitor, and ROSC resistor should

each be grounded to analog ground. The PVCC decoupling capacitors and VCLAMP capacitors should each

be grounded to power ground. Analog ground and power ground should be connected at the thermal pad,

which should be used as a central ground connection or star ground for the TPA3107D2.

•

Output filter—The ferrite EMI filter should be placed as close to the output terminals as possible for the best

EMI performance. The LC filter should be placed close to the outputs.

For an example layout, see the TPA3107D2 Evaluation Module User Manual, (SLOU190). Both the EVM user

manual and the thermal pad application note are available on the TI Web site at http://www.ti.com.

This application note focuses on methods that use the basic equipment listed below:

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Audio analyzer or spectrum analyzer

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Digital multimeter (DMM)

•

Oscilloscope

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Twisted-pair wires

•

Signal generator

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Power resistor(s)

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Linear regulated power supply

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Filter components

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EVM or other complete audio circuit

Figure 28 shows the block diagrams of basic measurement systems for class-AB and class-D amplifiers. A sine

wave is normally used as the input signal because it consists of the fundamental frequency only (no other

harmonics are present). An analyzer is then connected to the APA output to measure the voltage output. The

analyzer must be capable of measuring the entire audio bandwidth. A regulated dc power supply is used to

reduce the noise and distortion injected into the APA through the power pins. A System Two audio

measurement system (AP-II) (Reference 1) by Audio Precision includes the signal generator and analyzer in one

package.

The generator output and amplifier input must be ac-coupled. However, the EVMs already have the ac-coupling

attenuating the test signal, and is important because the input resistance of APAs is not high. Conversely, the

of milliohms and can be ignored for all but the power-related calculations.

Figure 28(a) shows a class-AB amplifier system. It takes an analog signal input and produces an analog signal

output. This amplifier circuit can be directly connected to the AP-II or other analyzer input.

This is not true of the class-D amplifier system shown in Figure 28(b), which requires low-pass filters in most

cases in order to measure the audio output waveforms. This is because it takes an analog input signal and

converts it into a pulse-width modulated (PWM) output signal that is not accurately processed by some

analyzers.

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