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USING LOW-ESR CAPACITORS
SHORT-CIRCUIT PROTECTION
LOW-SUPPLY VOLTAGE DETECTION
THERMAL PROTECTION
THERMAL CONSIDERATIONS: OUTPUT POWER AND MAXIMUM AMBIENT TEMPERATURE
ΘJA = 45.87°C/W
where: TJ = 125°C
TAmax = TJ – ΘJAPDissipated
(11)
PDissipated = PO(average) x ((1 / Efficiency) – 1)
Efficiency = ~85% for an 8-
load
= ~80% for a 4-
load
= ~75% for a 3-
load
(12)
TPA2008D2
SLOS413C – JULY 2003 – REVISED MAY 2004
APPLICATION INFORMATION (continued)
Low-ESR capacitors are recommended throughout this application section. A real (as opposed to ideal) capacitor
can be modeled simply as a resistor in series with an ideal capacitor. The voltage drop across this resistor
minimizes the beneficial effects of the capacitor in the circuit. The lower the equivalent value of this resistance
the more the real capacitor behaves like an ideal capacitor.
The TPA2008D2 has short circuit protection circuitry on the outputs that prevents damage to the device during
output-to-output shorts, output-to-GND shorts, and output-to-VDD shorts. When a short-circuit is detected on the
outputs, the part immediately goes into shutdown. This is a latched fault and must be reset by cycling the voltage
on the SHUTDOWN pin to a logic low and back to the logic high, or by cycling the power off and then back on.
This clears the short-circuit flag and allows for normal operation if the short was removed. If the short was not
removed, the protection circuitry activates again.
The TPA2008D2 incorporates circuitry designed to detect when the supply voltage is low. When the supply
voltage reaches 1.8 V or below, the TPA2008D2 goes into a state of shutdown. The current consumption drops
from millamperes to microamperes, leaving the remaining battery power for more essential devices such as
microprocessors. When the supply voltage level returns to normal, the device comes out of its shutdown state
and starts to draw current again. Note that even though the device is drawing several milliamperes of current, it
is not operationally functional until VDD≥ 4.5 V.
Thermal protection on the TPA2008D2 prevents damage to the device when the internal die temperature
exceeds 150
°C. There is a ±15 degree tolerance on this trip point from device to device. Once the die
temperature exceeds the thermal set point, the device enters into the shutdown state and the outputs are
disabled. This is not a latched fault. The thermal fault is cleared once the temperature of the die is reduced by
20
°C. The device begins normal operation at this point with no external system interaction.
To calculate the maximum ambient temperature, the following equation may be used:
(The derating factor for the 24-pin PWP package is given in the dissipation rating table.)
To estimate the power dissipation, the following equation may be used:
Example. What is the maximum ambient temperature for an application that requires the TPA2008D2 to drive 2
W into a 4-
speaker (stereo)?
PDissipated = 4 W x ((1 / 0.8) - 1) = 1 W
(PO = 2 W x 2)
TAmax = 125°C - (45.87°C/W x 1 W) = 79.13°C
19