Datasheet
TPA6204A1
SLOS429B − MAY 2004 − REVISED SEPTEMBER 2009
www.ti.com
12
Table 2 and Table 3 employ equation (5) to calculate
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 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 supply design. For a 1-W audio system
with 8-Ω loads and a 5-V supply, the maximum draw on the
power supply is almost 1.6 W.
A final point to remember about Class-AB amplifiers is how
to manipulate the terms in the efficiency equation to the
utmost advantage when possible.
A simple formula for calculating the maximum power
dissipated, P
Dmax
, may be used for a differential output
application:
P
Dmax
+
2V
2
DD
p
2
R
L
P
Dmax
for a 5-V, 8-Ω system is 0.64 W.
The maximum ambient temperature depends on the heat
sinking ability of the PCB system. The derating factor for
the 3 mm x 3 mm DRB package is shown in the dissipation
rating table. Converting this to Θ
JA
:
Θ
JA
+
1
Derating Factor
+
1
0.0218
+ 45.9°CńW
Given Θ
JA
, the maximum allowable junction temperature,
and the maximum internal dissipation, the maximum
ambient temperature can be calculated with the following
equation. The maximum recommended junction
temperature for the TPA6204A1 is 150°C.
T
A
Max + T
J
Max * Θ
JA
P
Dmax
+ 150 * 45.9
(
0.64
)
+ 120.6°C
Equation (8) shows that the maximum ambient
temperature is 120.6°C (package limited to 85°C)
at
maximum power dissipation with a 5-V supply.
Table 2 shows that for most applications no airflow is
required to keep junction temperatures in the specified
range. The TPA6204A1 is designed with thermal
protection that turns the device off when the junction
temperature surpasses 150°C to prevent damage to the
IC. In addition, using speakers with an impedance higher
than 8-Ω dramatically increases the thermal performance
by reducing the output current.
Table 2. Efficiency and Maximum Ambient Temperature vs Output Power in 3.6-V 8-Ω BTL Systems
Output Power
(W)
Efficiency
(%)
Internal Dissipation
(W)
Power From Supply
(W)
Max Ambient Temperature
(2)
(°C)
0.1 27.6 0.262 0.36 85
0.2 39.0 0.312 0.51 85
0.5 61.7 0.310 0.81 85
0.6 67.6 0.288 0.89 85
(1)
DRB package
(2)
Package limited to 85°C ambient
Table 3. Efficiency and Maximum Ambient Temperature vs Output Power in 5-V 8-Ω Systems
Output Power
(W)
Efficiency
(%)
Internal Dissipation
(W)
Power From Supply
(W)
Max Ambient Temperature
(2)
(°C)
0.5 44.4 0.625 1.13 85
1 62.8 0.592 1.60 85
1.36 73.3 0.496 1.86 85
1.7 81.9 0.375 2.08 85
(1)
DRB package
(2)
Package limited to 85°C ambient
PCB LAYOUT
It is important to keep the TPA6204A1 external components very close to the TPA6204A1 to limit noise pickup.
(6)
(7)
(8)