APA2065
Application Descriptions (Cont.)
assuming a 5V-power supply and an 8W load, must
BTL Amplifier Efficiency (Cont.)
not be greater than the power dissipation that results
denominator. This indicates that as VDD goes down,
efficiency goes up. In other words, use the efficiency
analysis to choose the correct supply voltage and
speaker impedance for the application.
from the equation15:
TJ,MAX - TA
(15)
PD,MAX=
qJA
For DIP-16 package with thermal pad, the thermal
resistance (qJA) is equal to 45oC/W.
Po (W) Efficiency (%) IDD(A) VPP(V) PD (W)
0.25
0.50
1.00
1.25
31.25
47.62
66.67
78.13
0.16
0.21
0.30
0.32
2.00
2.83
4.00
4.47
0.55
0.55
0.5
Since the maximum junction temperature (TJ,MAX) of
APA2065 is 150oC and the ambient temperature (TA)
is defined by the power system design, the maximum
power dissipation which the IC package is able to
handle can be obtained from equation15.
0.35
Once the power dissipation is greater than the
maximum limit (PD,MAX), either the supply voltage
(VDD) must be decreased, the load impedance (RL)
must be increased or the ambient temperature
should be reduced.
**High peak voltages cause the THDto increase.
Table 1. Efficiency Vs Output Power in 5-V/8W BTL
Systems
Power Dissipation
Whether the power amplifier is operated in BTLor SE
modes, power dissipation is a major concern. In
equation13 states the maximum power dissipation
point for a SE mode operating at a given supply
voltage and driving a specified load.
2
VDD
(13)
SE mode : PD,MAX=
2p2RL
In BTL mode operation, the output voltage swing is
doubled as in SE mode. Thus the maximum power
dissipationpoint for aBTLmode operatingat thesame
given conditions is 4 times as in SE mode.
2
4VDD
BTL mode : PD,MAX=
(14)
2p2RL
Since theAPA2065 is a dual channel power amplifier,
the maximum internal power dissipation is 2 times
that both of equations depending on the mode of
operation. Even with thissubstantial increase in power
dissipation, the APA2065 does not require extra
heatsink. The power dissipation from equation14,
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Rev. A.4 - Aug., 2005
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