TPA3007D1_17 Datasheet, PDF (14/24 Pages) Texas Instruments – 6.5-W MONO CLASS-D AUDIO POWER AMPLIFIER

TPA3007D1
SLOS418D – SEPTEMBER 2003 – REVISED MARCH 2008
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THERMAL CONSIDERATION: OUTPUT POWER AND RECOMMENDED
AMBIENT TEMPERATURE
To calculate the maximum ambient temperature, this equation can be used:
TA(max) + TJ * θ_{JAPDissipated}
where : TJ + 125°C
θ_JA
+
1
derating
factor
+
1
0.01145
+
87.3°CńW
(2)
(The derating factor for the 24-pin PW package is given in the dissipation rating table.)
To estimate the power dissipation, this equation can be used:
ǒǒ Ǔ Ǔ PDissipated + PO(average)
1
Efficiency
–1
Efficiency +X 85% for an 8-W load
(3)
Example: What is the maximum ambient temperature for an application that requires the TPA3007D1 to drive
3 W into an 8-Ω speaker?
P_Dissipated = 3 W x ((1 / 0.85) - 1) = 0.529 W
T_Amax = 125°C - (87.3°C/W x 0.529 W) = 78.8°C
This calculation shows that the TPA3007D1 can drive 3 W into an 8-Ω speaker up to the absolute maximum
ambient temperature rating of 78.8°C, which must never be exceeded.
GAIN SETTING VIA GAIN0 AND GAIN1 INPUTS
The gain of the TPA3007D1 is set by two input terminals, GAIN0 and GAIN1.
The gains listed in Table 2 are realized by changing the taps on the input resistors inside the amplifier. This
causes the input impedance (Z_I) to be dependent on the gain setting. The actual gain settings are controlled by
ratios of resistors, so the gain variation from part-to-part is small. However, the input impedance may shift by
30% due to shifts in the actual resistance of the input resistors.
For design purposes, the input network (discussed in the next section) should be designed assuming an input
impedance of 23 kΩ, which is the absolute minimum input impedance of the TPA3007D1. At the lower gain
settings, the input impedance could increase as high as 313 kΩ.
GAIN1
0
0
1
1
GAIN0
0
1
0
1
Table 2. Gain Settings
AMPLIFIER GAIN
(dB)
TYP
12
18
23.6
36
INPUT IMPEDANCE
(kΩ)
TYP
241
168
104
33
INPUT RESISTANCE
Each gain setting is achieved by varying the input resistance of the amplifier, which can range from its smallest
value to over six times that value. As a result, if a single capacitor is used in the input high-pass filter, the -3 B or
cutoff frequency also changes by over six times.
14
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