apa4838 Anpec Electronics Corporation, apa4838 Datasheet - Page 24

• Manufacturer Part Number: apa4838
• Description: Stereo 2.8w Audio Power Amplifier With Dc Volume Control And Selectable Gain
• Manufacturer: Anpec Electronics Corporation

APA4838
Application Descriptions (Cont.)
BTL Amplifier Efficiency (Cont.)
The efficiency of the amplifier is quite low for lower
power levels and rises sharply as power to the load
is increased resulting in a nearly flat internal power
dissipation over the normal operating range. Note
that the internal dissipation at full output power is less
than in the half power range. Calculating the efficiency
for a specific system is the key to proper power sup-
ply design. For a stereo 1W audio system with 8
loads and a 5V supply, the maximum draw on the
power supply is almost 3W.
A final point to remember about linear amplifiers
(either SE or BTL) is how to manipulate the terms in
the efficiency equation to utmost advantage when
possible. Note that in equation, V
denominator. This indicates that as V
efficiency goes up. In other words, use the efficiency
analysis to choose the correct supply voltage and
speaker impedance for the application.
Power Dissipation
Whether the power amplifier is operated in BTL or
SE modes, power dissipation is a major concern. In
equation14 states the maximum power dissipation
point for a SE mode operating at a given supply volt-
age and driving a specified load.
In BTL mode operation, the output voltage swing is
doubled as in SE mode. Thus the maximum power
dissipation point for a BTL mode operating at the
same given conditions is 4 times as in SE mode.
Copyright
Rev. A.1 - Apr., 2003
SE mode : P
ANPEC Electronics Corp.
D,MAX
=
2 R
V
DD
2
2
L
DD
DD
goes down,
is in the
(14)
24
Power Dissipation (Cont.)
Since the APA4838 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 this substantial increase in power
dissipation, the APA4838 does not require extra
heatsink. The power dissipation from equation15,
assuming a 5V-power supply and an 8
not be greater than the power dissipation that results
from the equation16:
For TSSOP-28 package with and without thermal pad,
the thermal resistance (
50 C/W, respectively.
Since the maximum junction temperature (T
APA4838 is 150 C and the ambient temperature (T
is defined by the power system design, the maximum
power dissipation which the IC package is able to
handle can be obtained from equation16. Once the
power dissipation is greater than the maximum limit
(P
decreased, the load impedance (R
creased or the ambient temperature should be
reduced.
D,MAX
BTL mode : P
P
D,MAX
), either the supply voltage (V
=
T
J,MAX
JA
- T
D,MAX
A
=
2 R
4V
JA
2
DD
) is equal to 45 C/W and
L
2
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L
) must be in-
DD
load, must
) must be
J,MAX
(15)
(15)
) of
A
)