Datasheet

P
dB
+ 10Log
P
W
P
ref
+ 10Log
4 W
1 W
+ 6 dB
P
W
+ 10
PdBń10
P
ref
= 250 mW (12-db crest factor)
= 125 mW (15-db crest factor)
= 63 mW (18-db crest factor)
= 500 mW (9-db crest factor)
= 1000 mW (6-db crest factor)
= 2000 mW (3-db crest factor)
TPA6013A4
www.ti.com SLOS635 –NOVEMBER 2009
Table 5. Efficiency vs Output Power in 5-V, 8-Ω BTL Systems
OUTPUT POWER EFFICIENCY PEAK VOLTAGE INTERNAL DISSIPATION
(W) (%) (V) (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 8, V
DD
is in the denominator. This
indicates that as V
DD
goes down, efficiency goes up.
CREST FACTOR AND THERMAL CONSIDERATIONS
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 TPA6013A4 data sheet, one can
see that when the TPA6013A4 is operating from a 5-V supply into a 3-Ω speaker, that 4-W peaks are available.
Use equation 9 to convert watts to dB.
(9)
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)
To convert dB back into watts use equation 10.
(10)
This is valuable information to consider when attempting to estimate the heat dissipation requirements for the
amplifier system. Comparing the worst case, which is 2 W of continuous power output with a 3-dB crest factor,
against 12-dB and 15-dB applications significantly affects maximum ambient temperature ratings for the system.
Using the power dissipation curves for a 5-V, 3-Ω system, the internal dissipation in the TPA6013A4 and
maximum ambient temperatures is shown in Table 6.
Copyright © 2009, Texas Instruments Incorporated Submit Documentation Feedback 23
Product Folder Link(s) :TPA6013A4