
100°C/W
JA
DMAX
T
P
C
A
J
Max =
Max -
= 150 - 100 (0.4) = 110
q
°
Ferrite
ChipBead
Ferrite
ChipBead
1nF
OUTP
OUTN
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SLOS649A – MARCH 2010 – REVISED JANUARY 2011
EFFICIENCY AND THERMAL INFORMATION
The maximum ambient temperature depends on the heat-sinking ability of the PCB system. The derating factor
for the package is shown in the dissipation rating table. Converting this to qJA for the WCSP package:
(7)
Given qJA of 100°C/W, the maximum allowable junction temperature of 150°C, and the maximum internal
dissipation of 0.4 W (0.2 W per channel) for 1.5 W per channel, 8-
maximum ambient temperature can be calculated with the following equation.
(8)
Equation 8 shows that the calculated maximum ambient temperature is 110°C at maximum power dissipation
with a 5-V supply and 8-
a load. The TPA2026D2 is designed with thermal protection that turns the device off
when the junction temperature surpasses 150°C to prevent damage to the IC. Also, using speakers more
resistive than 8-
dramatically increases the thermal performance by reducing the output current and increasing
the efficiency of the amplifier.
OPERATION WITH DACS AND CODECS
In using Class-D amplifiers with CODECs and DACs, sometimes there is an increase in the output noise floor
from the audio amplifier. This occurs when output frequencies of the CODEC/DAC mix with the Class-D
switching frequency and create sum/difference components in the audio band. The noise increase can be solved
by placing an RC low-pass filter between the CODEC/DAC and audio amplifier. The filter reduces high
frequencies that cause the problem and allows proper performance.
SHORT CIRCUIT AUTO-RECOVERY
When a short circuit event happens, the TPA2026D2 goes to low duty cycle mode and tries to reactivate itself
every 110 s. This auto-recovery will continue until the short circuit event stops. This feature can protect the
device without affecting the device's long term reliability. FAULT bit (register 1, bit 3) still requires a write to clear.
FILTER FREE OPERATION AND FERRITE BEAD FILTERS
A ferrite bead filter can often be used if the design is failing radiated emissions without an LC filter and the
frequency sensitive circuit is greater than 1 MHz. This filter functions well for circuits that just have to pass FCC
and CE because FCC and CE only test radiated emissions greater than 30 MHz. When choosing a ferrite bead,
choose one with high impedance at high frequencies, and low impedance at low frequencies. In addition, select a
ferrite bead with adequate current rating to prevent distortion of the output signal.
Use an LC output filter if there are low frequency (< 1 MHz) EMI sensitive circuits and/or there are long leads
from amplifier to speaker.
Figure 48 shows typical ferrite bead and LC output filters.
Figure 48. Typical Ferrite Bead Filter (Chip bead example: TDK: MPZ1608S221A)
Copyright 2010–2011, Texas Instruments Incorporated
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