TPA2050D4 Datasheet, PDF (24/29 Pages) Texas Instruments – 1.4 W/CH STEREO CLASS-D AUDIO SUBSYSTEM WITH DirectPath™ HEADPHONE AMPLIFIER AND 2:1 INPUT MUX

TPA2050D4
SLOS544 – JULY 2008....................................................................................................................................................................................................... www.ti.com
EFFICIENCY AND THERMAL INFORMATION
The maximum ambient temperature depends on the heat-sinking ability of the PCB system. The derating factor
for the packages are shown in the dissipation rating table. Converting this to θ_JA for the WCSP package:
q_JA
=
1
Derating Factor
=
1
0.009
= 111°C/W
(3)
Given θ_JA of 111°C/W, the maximum allowable junction temperature of 150°C, and the maximum internal
dissipation of 0.12 W (0.06 W per channel) for 1.4 W per channel, 8-Ω load, 5-V supply, from Figure 25 , the
maximum ambient temperature can be calculated with the following equation:
T_AMax = T_JMax - θ_JAP_DMAX = 150 - 111(0.12) = 137°C
(4)
Equation 4 shows that the calculated maximum ambient temperature is 137°C at maximum power dissipation
with a 5-V supply and 8-Ω a load. The TPA2050D4 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-Ω 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 mixing of the output frequencies of the CODEC/DAC mix with the
switching frequencies of the audio amplifier input stage. The noise increase can be solved by placing a low-pass
filter between the CODEC/DAC and audio amplifier. This filters off the high frequencies that cause the problem
and allow proper performance. See the functional block diagram.
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 49 shows typical ferrite bead and LC output filters.
OUTP
Ferrite
Chip Bead
OUTN
Ferrite
Chip Bead
1 nF
1 nF
Figure 49. Typical Ferrite Bead Filter (Chip bead example: TDK: MPZ1608S221A)
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