參數(shù)資料
型號: TPA0152PWPG4
廠商: TEXAS INSTRUMENTS INC
元件分類: 音頻控制
英文描述: 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, PDSO24
封裝: GREEN, PLASTIC, HTSSOP-24
文件頁數(shù): 17/32頁
文件大?。?/td> 651K
代理商: TPA0152PWPG4
www.ti.com
CREST FACTOR AND THERMAL CONSIDERATIONS
P
dB + 10 Log
P
W
P
ref
+ 10 Log
4 W
1 W
+ 6 dB
(10)
TPA0152
SLOS246F – JUNE 1999 – REVISED SEPTEMBER 2004
Table 2. Efficiency vs Output Power in 5-V, 8-
BTL Systems
EFFICIENCY
OUTPUT POWER (W)
PEAK VOLTAGE (V)
INTERNAL DISSIPATION (W)
(%)
0.25
31.4
2.00
0.55
0.50
44.4
2.83
0.62
1.00
62.8
4.00
0.59
1.25
70.2
4.47(1)
0.53
(1)
High peak voltages cause the THD to increase.
A final point to remember about Class-AB amplifiers (either SE or BTL) is how to manipulate the terms in the
efficiency equation to utmost advantage when possible. Note that in Equation 9, VDD is in the denominator. This
indicates that as VDD goes down, efficiency goes up.
Class-AB power amplifiers dissipate a significant amount of heat in the package under normal operating
conditions. A typical music CD requires 12 dB to 15 dB of dynamic range, or headroom, above the average
power output, to pass the loudest portions of the signal without distortion. In other words, music typically has a
crest factor between 12 dB and 15 dB. When determining the optimal ambient operating temperature, the internal
dissipated power at the average output power level must be used. From the data sheet, one can see that when
the device is operating from a 5-V supply into a 3-
speaker that 4-W peaks are available. Use Equation 10 to
convert watts to dB.
Subtracting the headroom restriction to obtain the average listening level without distortion yields:
6 dB - 15 dB = -9 dB (15-dB crest factor)
6 dB - 12 dB = -6 dB (12-dB crest factor)
6 dB - 9 dB = -3 dB (9-dB crest factor)
6 dB - 6 dB = 0 dB (6-dB crest factor)
6 dB - 3 dB = 3 dB (3-dB crest factor)
Converting dB back into watts:
PW = 10
PdB/10
× P
ref
= 63 mW (18-dB crest factor)
= 125 mW (15-dB crest factor)
= 250 mW (9-dB crest factor)
= 500 mW (6-dB crest factor)
= 1000 mW (3-dB crest factor)
= 2000 mW (0-dB crest factor)
This is valuable information to consider when estimating the heat-dissipation requirements for the amplifier
system. Comparing the worst case, 2 W of continuous power output with a 3-dB crest factor, against 12-dB and
15-dB applications, drastically affects maximum ambient temperature ratings for the system. Using the power
dissipation curves for a 5-V, 3-
system, the internal dissipation and maximum ambient temperatures are shown
in the table below.
24
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