Datasheet

EFFICIENCY AND THERMAL INFORMATION
=
1
Derating Factor
1
0.0218
=45.9 C/W
o
q
JA
=
(17)
T
A J JA Dmax
Max= T Max P =125 45.9(0.2)=115.8 C- q -
o
(18)
ELIMINATING THE OUTPUT FILTER WITH THE TPA2006D1
Effect on Audio
Traditional Class-D Modulation Scheme
0 V
-5 V
+5 V
Current
OUT+
Differential Voltage
Across Load
OUT-
TPA2006D1
www.ti.com ................................................................................................................................................. SLOS498A – SEPTEMBER 2006 – REVISED JULY 2008
The maximum ambient temperature depends on the heat-sinking ability of the PCB system. The derating factor
for the DRB package is shown in the dissipation rating table. Converting this to θ
JA
:
Given θ
JA
of 45.9 ° C/W, the maximum allowable junction temperature of 125 ° C, and the maximum internal
dissipation of 0.2 W (Po=1.45 W, 8- Ω load, 5-V supply, from Figure 3 ), the maximum ambient temperature can
be calculated with the following equation.
Equation 18 shows that the calculated maximum ambient temperature is 115.8 ° C at maximum power dissipation
with a 5-V supply and 8- Ω a load, see Figure 3 . The TPA2006D1 is designed with thermal protection that turns
the device off when the junction temperature surpasses 150 ° C to prevent damage to the IC.
This section focuses on why the user can eliminate the output filter with the TPA2006D1.
The class-D amplifier outputs a pulse-width modulated (PWM) square wave, which is the sum of the switching
waveform and the amplified input audio signal. The human ear acts as a band-pass filter such that only the
frequencies between approximately 20 Hz and 20 kHz are passed. The switching frequency components are
much greater than 20 kHz, so the only signal heard is the amplified input audio signal.
The traditional class-D modulation scheme, which is used in the TPA005Dxx family, has a differential output
where each output is 180 degrees out of phase and changes from ground to the supply voltage, V
DD
. Therefore,
the differential pre-filtered output varies between positive and negative V
DD
, where filtered 50% duty cycle yields
0 volts across the load. The traditional class-D modulation scheme with voltage and current waveforms is shown
in Figure 33 . Note that even at an average of 0 volts across the load (50% duty cycle), the current to the load is
high causing a high loss and thus causing a high supply current.
Figure 33. Traditional Class-D Modulation Scheme's Output Voltage and Current Waveforms Into an
Inductive Load With no Input
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