AA4002 Datasheet, PDF (17/22 Pages) BCD Semiconductor Manufacturing Limited – STEREO 2W AUDIO POWER AMPLIFIER

Data Sheet
STEREO 2W AUDIO POWER AMPLIFIER
AA4002
Application Information (Continued)
V_DD(V)
(pin6,16,27)
Here T_JMAX is maximum operating junction
temperature 150^oC, 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^oC/W
given in datasheet page 6.
Mute(V)
(pin5)
Assuming T_A is +25^oC, the maximum allowed power
dissipation P_DMAX is about 2.78W according to
formula 12.
Shutdown(V)
(pin2)
OFF STBY MUTE
PLAY
MUTE STBY OFF
There is the other formula about power dissipation
drawn from application for each channel which is
determined by supply voltage and load resistance.
P_DSEMAX
=
V_DD ²
2π ²R_L
(for SE mode)....................(13)
Figure 24. Recommended Sequences for Power ON/OFF
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,
η = ^{πVP ........................................................(11)}
4V_DD
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.
P_DMAX
=
T_JMAX − T_A
θ _JA
........................................(12)
P_DBTLMAX
=
2V_DD ²
π ² R_L
(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=4Ω,
stereo in BTL mode,
P_DBTLMAX
=
2V_DD ²
π ²R_L
=
2 × 5²
3.14² × 4
= 1.266W
, 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,
T_A = T_JMAX −θ _JA ∗ P_DBTLMAX =150-45*2.53=36.2 ^oC
That is to say, if user wants AA4002 can delivery
maximum output power to 4Ω load, at V_DD=5.0V, BTL
mode, ambient temperature has to hold less than
36.2^oC. When junction temperature exceeds about
+165^oC, thermal shutdown circuit built-in AA4002
Sep. 2006 Rev. 1. 1
BCD Semiconductor Manufacturing Limited
17