APA2068
Application Descriptions (Cont.)
BTL Amplifier Efficiency (Cont.)
tion13 states the maximum power dissipation point
for aSE mode operating at a given supplyvoltage and
driving a specifiedload.
loadisincreased resultingin anearlyflat internal power
dissipation over the normal operating range.
2
VDD
(13)
SE mode : PD,MAX=
2p2RL
Note that the efficiency of the amplifier is quite low for
lower power levels and rises sharply as power to the
loadisincreased resultingin anearlyflat internal power
dissipation over the normal operating range. Notethat
the internal dissipation at full output power is less than
in the half power range. Calculatingthe efficiency for a
specific system is the key to proper power supply
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
(14)
BTL mode : PD,MAX=
2p2RL
design. For a stereo 1W audio system with 8W loads Since theAPA2068 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 APA2068 does not require extra
heatsink. The power dissipation from equation14,
assuming a 5V-power supply and an 8W load, must
not be greater than the power dissipation that results
and a 5V supply, the maximum draw on the power
supply is almost 3W.
Afinal point toremember about linear amplifiers(either
SE or BTL) is how to manipulate the terms in the
efficiencyequationtoutmost advantagewhenpossible.
Note that in equation, VDD is in the 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 SOP16-P package with thermal pad, the thermal
resistance (qJA) is equal to 45oC/W.
Po (W) Efficiency (%) IDD(A) VPP(V) PD (W)
Since the maximum junction temperature (TJ,MAX) of
APA2068 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.
0.25
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
Once the power dissipation is greater than the maxi-
mum limit (PD,MAX), either the supplyvoltage (VDD) must
be decreased, the load impedance (RL) must be in-
creasedor theambient temperatureshouldbereduced.
0.35
**High peak voltages cause the THDto increase.
Table 1. Efficiency Vs Output Power in 5-V/8W BTL
Systems
Thermal Pad Considerations
Power Dissipation
The thermal pad must be connected to ground. The
Whether the power amplifier is operated in BTLor SE package with thermal pad of the APA2068 requires
modes, power dissipation isa major concern. Inequa- special attention on thermal design. If the thermal
Copyright ã ANPEC Electronics Corp.
22
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Rev. A.2 - Jul., 2005
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