
STEREO 2W AUDIO POWER AMPLIFIER
AA4002
Data Sheet
17
Sep. 2006 Rev. 1. 1
BCD Semiconductor Manufacturing Limited
Application Information
(Continued)
1) Power ON operation, enable mute, then enable
shutdown; after V
DD
is stable, release shutdown first,
then mute.
2) Power OFF, enable mute, then enable shutdown;
after V
DD
is discharged completely, release shutdown
firstly, then mute.
Efficiency, Power Dissipation and Thermal
Consideration in Design
For Class-AB amplifier, Figure 11 is the basic equation
of efficiency worked in BTL configuration,
........................................................(11)
Here V
P
is peak voltage of output swing.
Thermal dissipation becomes major concern when
output power is close to 2W especially in BTL mode.
The maximum power dissipation of package for
AA4002 can be calculated by following equation.
........................................(12)
Here T
JMAX
is maximum operating junction
temperature 150
o
C, T
A
is ambient temperature,
θ
JA
is
thermal resistance form junction to ambient. For G
package (TSSOP-28 with exposed DAP), it is 45
o
C/W
given in datasheet page 6.
Assuming T
A
is +25
o
C, the maximum allowed power
dissipation P
DMAX
is about 2.78W according to
formula 12.
There is the other formula about power dissipation
drawn from application for each channel which is
determined by supply voltage and load resistance.
(for SE mode)....................(13)
(for BTL mode).................(14)
If power dissipation calculated by application is larger
than permissible by package, it is necessary to
assemble additional heat sinking, or keep ambient
temperature around the chip very low, or increasing
load impedance, or decreasing power supply voltage.
Here is an example, assuming V
DD
=5.0V, R
L
=4
,
stereo in BTL mode,
, for 2 channels, total power dissipation P
DTOTAL
=2*
P
DBTLMAX
=2*1.266=2.53W, according to formula 13,
the maxim ambient temperature is,
=150-45*2.53=36.2
o
C
That is to say, if user wants AA4002 can delivery
maximum output power to 4
load, at V
DD
=5.0V, BTL
mode, ambient temperature has to hold less than
36.2
o
C. When junction temperature exceeds about
+165
o
C, thermal shutdown circuit built-in AA4002
Figure 24. Recommended Sequences for Power ON/OFF
V
(V)
(pin6,16,27)
Mute(V)
(pin5)
Shutdown(V)
(pin2)
STBY MUTE
STBY
MUTE
OFF
OFF
PLAY
DD
P
V
V
4
π
η
=
JA
A
JMAX
T
DMAX
P
T
θ
=
L
DD
2
DSEMAX
P
R
V
2
π
2
=
L
DD
R
DBTLMAX
P
V
2
2
2
π
=
W
R
V
P
L
DD
2
DBTLMAX
266
.
=
4
14
.
5
2
2
2
2
2
×
×
=
=π
DBTLMAX
P
JA
JMAX
T
A
T
=
θ