apa3012 Anpec Electronics Corporation, apa3012 Datasheet - Page 16

• Manufacturer Part Number: apa3012
• Description: 3w Mono Low-voltage Audio Power Amplifier
• Manufacturer: Anpec Electronics Corporation

Application Information (Cont.)
The following equations are the basis for calculating
amplifier efficiency.
Table 1 calculates efficiencies for four different output
power levels.
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.
Note that the internal dissipation at full output power is
less than in the half power range. Calculating the effi-
ciency for a specific system is the key to proper power
supply design.
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
cates that as V
words, use the efficiency analysis to choose the correct
supply voltage and speaker impedance for the application.
Table 1. Efficiency Vs Output Power in 5-V/8
Systems.
Copyright
Rev. A.2 - Dec., 2008
Efficiency of a BTL configuration :
BTL Amplifier Efficiency (Cont.)
Where :
APA3012
** High peak voltages cause the THD to increase.
Po (W)
0.25
0.50
1.00
1.25
Efficiency =
P
P
V
P
O
P
SUP
rms
SUP
O
V
rms
V
V
(
V
2
DD
P
R
Efficiency (%)
P
ANPEC Electronics Corp.
2
L
R
DD
V
L
V
I
rms
DDAVG
goes down, efficiency goes up. In other
P
31.25
47.62
66.67
78.13
P
P
SUP
)
O
/(
V
V
DD
DD
P
2
V
R
is in the denominator. This indi-
DD
L
V
2
V
R
P
P
L
)
I
2V
DD
0.16
0.21
0.30
0.32
R
(A)
P
4
L
V
V
DD
P
V
2.00
2.83
4.00
4.47
PP
(V)
(10)
P
0.55
0.55
0.35
(7)
D
(8)
(9)
(6)
0.5
(W)
BTL
16
Power Dissipation
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.
Even with this substantial increase in power dissipation,
the APA3012 does not require extra heatsink. The power
dissipation from equation11, assuming a 5V-power sup-
ply and an 8
dissipation that results from the equation12 :
For MSOP-8P package with thermal pad, the thermal re-
sistance (
Since the maximum junction temperature (T
APA3012 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 equation11.
Once the power dissipation is greater than the maximum
limit (P
decreased, the load impedance (R
or the ambient temperature should be reduced.
Thermal Pad Consideration
The thermal pad must be connected to the ground. The
package with thermal pad of the APA3012 requires spe-
cial attention on thermal design. If the thermal design
issues are not properly addressed, the APA3012 4
go into thermal shutdown when driving a 4
The thermal pad on the bottom of the APA3012 should be
soldered down to a copper pad on the circuit board. Heat
can be conducted away from the thermal pad through the
copper plane to ambient. If the copper plane is not on the
top surface of the circuit board, 8 to 12 vias of 15 mil or
smaller in diameter should be used to thermally couple
the thermal pad to the bottom plane.
For good thermal conduction, the vias must be plated
through and solder filled. The copper plane used to con-
duct heat away from the thermal pad should be as large
as practical.
BTL mode :
P
, D
MAX
D,MAX
JA
), either the supply voltage (V
T
) is equal to 50 C/W.
, J
MAX
load, must not be greater than the power
JA
P
, D
T
MAX
A
2
4
V
DD
2
R
2
L
L
) must be increased
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DD
load.
) must be
J,MAX
(12)
(11)
A
) of
) is
will