12.1 Layout Guidelines

The TPA3138D2 device can be used with a small, inexpensive ferrite bead output filter for most applications. However, since the Class-D switching edges are fast, it is necessary to take care when planning the layout of the printed circuit board. The following suggestions help meet EMC requirements.

• Decoupling capacitors—The high-frequency decoupling capacitors should be placed as close to the PVCC and AVCC pins as possible. Large (100-µF or greater) bulk power supply decoupling capacitors should be placed near the TPA3138D2 device on the PVCC supplies. Local, high-frequency bypass capacitors should be placed as close to the PVCC pins as possible. These caps can be connected to the thermal pad directly for an excellent ground connection. Consider adding a small, good quality low ESR ceramic capacitor between 220 pF and 1000 pF and a larger mid-frequency cap of value between 0.1 μF and 1 μF also of good quality to the PVCC connections at each end of the chip.
• Keep the current loop from each of the outputs through the ferrite bead and the small filter cap and back to GND as small and tight as possible. The size of this current loop determines its effectiveness as an antenna.
• Grounding—The AVCC (pin 7) decoupling capacitor should be connected to ground (GND). The PVCC decoupling capacitors should connect to GND. 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 TPA3138D2.
• Output filter—The ferrite EMI filter (Figure 22) should be placed as close to the output pins as possible for the best EMI performance. The capacitors used in the ferrite should be grounded to power ground.
• Thermal Pad—The thermal pad must be soldered to the PCB for proper thermal performance and optimal reliability. The dimensions of the thermal pad and thermal land should be 3.04 mm × 2.34 mm. Seven rows of solid vias (three vias per row, 0.3302 mm or 13 mils diameter) should be equally spaced underneath the thermal land. The vias should connect to a solid copper plane, either on an internal layer or on the bottom layer of the PCB. The vias must be solid vias, not thermal relief or webbed vias. See the TI Application Report SLMA002 for more information about using the TSSOP thermal pad. For recommended PCB footprints, see figures at the end of this data sheet.

For an example layout, see the TPA3138D2 Evaluation Module (TPA3138D2EVM) User Manual. Both the EVM user manual and the thermal pad application report are available on the TI Web site at http://www.ti.com.