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SHORT-CIRCUIT PROTECTION AND AUTOMATIC RECOVERY FEATURE

THERMAL PROTECTION

PRINTED-CIRCUIT BOARD (PCB) LAYOUT

TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
The TPA3008D2 has short-circuit protection circuitry on the outputs that prevents damage to the device duringoutput-to-output shorts, output-to-GND shorts, and output-to-V
CC
shorts. When a short circuit is detected on theoutputs, the part immediately disables the output drive. This is a latched fault and must be reset by cycling thevoltage on the SHUTDOWN pin to a logic low and back to the logic high state for normal operation. This clearsthe short-circuit flag and allows for normal operation if the short was removed. If the short was not removed, theprotection circuitry again activates.
The fault terminal can be used for automatic recovery from a short-circuit event, or used to monitor the statuswith an external GPIO.
Thermal protection on the TPA3008D2 prevents damage to the device when the internal die temperatureexceeds 150°C. There is a ±15 degree tolerance on this trip point from device to device. Once the dietemperature exceeds the thermal set point, the device enters into the shutdown state and the outputs aredisabled. This is not a latched fault. The thermal fault is cleared once the temperature of the die is reduced by20°C. The device begins normal operation at this point with no external system interaction.
Because the TPA3008D2 is a class-D amplifier that switches at a high frequency, the layout of the printed-circuitboard (PCB) should be optimized according to the following guidelines for the best possible performance.
•Decoupling capacitors—The high-frequency 0.1-µF decoupling capacitors should be placed as close to thePVCC (pins 14, 15, 22, 23, 38, 39, 46, and 47) and AV
CC
(pin 33) terminals as possible. The V2P5 (pin 4)capacitor, AV
DD
(pin 29) capacitor, and VCLAMP (pins 25 and 36) capacitor should also be placed as closeto the device as possible. Large (10 µF or greater) bulk power supply decoupling capacitors should beplaced near the TPA3008D2 on the PVCCL, PVCCR, and AV
CC
terminals.
•Grounding—The AV
CC
(pin 33) decoupling capacitor, AV
DD
(pin 29) capacitor, V2P5 (pin 4) capacitor, COSC(pin 28) capacitor, and ROSC (pin 27) resistor should each be grounded to analog ground (AGND, pins 26and 30). The PVCC decoupling capacitors should each be grounded to power ground (PGND, pins 18, 19,42, and 43). Analog ground and power ground may be connected at the PowerPAD, which should be usedas a central ground connection or star ground for the TPA3008D2. Basically, an island should be createdwith a single connection to PGND at the PowerPAD.
•Output filter—The ferrite EMI filter (Figure 20 ) should be placed as close to the output terminals as possiblefor the best EMI performance. The LC filter (Figure 19 ) should be placed close to the outputs. The capacitorsused in both the ferrite and LC filters should be grounded to power ground. If both filters are used, the LCfilter should be placed first, following the outputs.
•PowerPAD—The PowerPAD must be soldered to the PCB for proper thermal performance and optimalreliability. The dimensions of the PowerPAD thermal land should be 5 mm by 5 mm (197 mils by 197 mils).The PowerPAD size measures 4,55 x 4,55 mm. Four rows of solid vias (four vias per row, 0,3302 mm or 13mils diameter) should be equally spaced underneath the thermal land. The vias should connect to a solidcopper plane, either on an internal layer or on the bottom layer of the PCB. The vias must be solid vias, notthermal relief or webbed vias. For additional information, see the PowerPAD Thermally Enhanced Packageapplication note, (SLMA002).
For an example layout, see the TPA3008D2 Evaluation Module (TPA3008D2EVM) User Manual, (SLOU165).Both the EVM user manual and the PowerPAD application note are available on the TI Web site athttp://www.ti.com.
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