TPA2012D2
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SLOS438C–DECEMBER 2004–REVISED MARCH 2007
Trace Width
Recommended trace width at the solder balls is 75 µm to 100 µm to prevent solder wicking onto wider PCB
traces.
For high current pins (PVDD, PGND, and audio output pins) of the TPA2012D2, use 100-µm trace widths at the
solder balls and at least 500-µm PCB traces to ensure proper performance and output power for the device.
For the remaining signals of the TPA2012D2, use 75-µm to 100-µm trace widths at the solder balls. The audio
input pins (INR+/- and INL+/-) must run side-by-side to maximize common-mode noise cancellation.
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 θJA for the QFN package:
1
1
q
+
+
+ 24°CńW
JA
0.041
Derating Factor
(3)
Given θJA of 24°C/W, the maximum allowable junction temperature of 150°C, and the maximum internal
dissipation of 1.5W (0.75 W per channel) for 2.1 W per channel, 4-Ω load, 5-V supply, from Figure 25, the
maximum ambient temperature can be calculated with the following equation.
T Max + T Max * q
P
+ 150 * 24 (1.5) + 114°C
A
J
JA Dmax
(4)
Equation 4 shows that the calculated maximum ambient temperature is 114°C at maximum power dissipation
with a 5-V supply and 4-Ω a load. The TPA2012D2 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 4-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 Figure 33 for the 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 very 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 37 shows typical ferrite bead and LC output filters.
Ferrite
Chip Bead
OUTP
1 nF
Ferrite
Chip Bead
OUTN
1 nF
Figure 37. Typical Ferrite Chip Bead Filter (Chip bead example: TDK: MPZ1608S221A)
14
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