apa2071 Anpec Electronics Corporation, apa2071 Datasheet - Page 19

• Manufacturer Part Number: apa2071
• Description: Stereo 3.1w Non-inverting Audio Power Amplifier With Dc Volume Control
• Manufacturer: Anpec Electronics Corporation

APA2071
BTL Amplifier Efficiency (Cont.)
Note that 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 dissi-
pation over the normal operating range. In addition, 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 supply design. For a
stereo 1W audio system with 8
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 effi-
ciency equation to utmost advantage when possible. Note
that in equation, V
that as V
use the efficiency analysis to choose the correct supply
voltage and speaker impedance for the application.
**High peak voltages cause the THD+N to increase.
Table 1. Efficiency vs. Output Power in 5-V/8
tems
Power Dissipation
Whether the power amplifier is operated in BTL or SE
mode, power dissipation is the major concern. Equation
(14) states the maximum power dissipation point for a
SE mode operating at a given supply voltage and driving
a specified load.
In BTL mode operation, the output voltage swing is
doubled as in SE mode. Thus, the maximum power dis-
sipation point for a BTL mode operating at the same given
conditions is 4 times as in SE mode.
Copyright
Rev. A.1 - Aug., 2008
Application Information (Cont.)
Po (W)
0.25
0.50
1.00
1.25
SE
mode
DD
goes down, efficiency goes up. In other words,
P :
Efficiency (%)
ANPEC Electronics Corp.
D,
MAX
31.25
47.62
66.67
78.13
DD
=
2
is in the denominator. This indicates
V
DD
2
R
2
L
I
DD
0.16
0.21
0.30
0.32
(A)
loads and a 5V supply,
V
2.00
2.83
4.00
4.47
PP
(V) P
BTL Sys-
(12)
0.55
0.55
0.35
D
0.5
(W)
19
Since the APA2071 is a dual channel power amplifier, the
maximum internal power dissipation is 2 times that both
of equations depend on the mode of operation. Even with
this substantial increase in power dissipation, the
APA2071 does not require extra heatsink. The power dis-
sipation from equation (14), assuming a 5V-power sup-
ply and an 8
dissipation that results from the equation (16):
For DIP-16 package, the thermal resistance (
to 45 C/W.
Since the maximum junction temperature (T
APA2071 is 150 C and the ambient temperature (T
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
or the ambient temperature should be reduced.
Thermal Consideration
Linear power amplifiers dissipate a significant amount of
heat in the package under normal operating conditions.
The first consideration to calculate maximum ambient
temperatures is the numbers from the Power Dissipa-
tion vs. Output Power graphs are per channel values, so
the dissipation of the IC heat needs to be doubled for
two-channel operation. Given
able junction temperature (T
dissipation (P
be calculated with the following equation. The maximum
recommended junction temperature for the APA2071 is
150°C. The internal dissipation figures are taken from
the Power Dissipation vs. Output Power graphs.
BTL
P
150 - 45(0.8*2) = 78°C
T
D,
AMax
MAX
D,MAX
mode
= T
), either the supply voltage (V
JMax
T
D
J,
), the maximum ambient temperature can
:
load, must not be greater than the power
P
MAX
-
D,
JA
JA
MAX
P
-
T
D
A
=
4V
2
2
DD
R
JMAX
2
L
JA
), and the total internal
, the maximum allow-
L
) must be increased
www.anpec.com.tw
DD
J,MAX
JA
) must be
) is equal
(
13)
(14)
(15)
) of the
A
) is