Datasheet
θ
JA
+
1
Derating Factor
+
1
0.0218
+ 45.9°CńW
T
A
Max + T
J
Max * θ
JA
P
Dmax
+ 150 * 45.9
(
1.27
)
+ 91.7°C
P
Dmax
+
2V
2
DD
p
2
R
L
TPA6211A1
SLOS367D –AUGUST 2003– REVISED JUNE 2011
www.ti.com
Table 2 employs Equation 15 to calculate efficiencies The maximum ambient temperature depends on the
for four different output power levels. Note that the heat sinking ability of the PCB system. The derating
efficiency of the amplifier is quite low for lower power factor for the 3 mm ×3 mm DRB package is shown in
levels and rises sharply as power to the load is the dissipation rating table. Converting this to θ
JA
:
increased resulting in a nearly flat internal power
dissipation over the normal operating range. Note that
(17)
the internal dissipation at full output power is less
than in the half power range. Calculating the Given θ
JA
, the maximum allowable junction
efficiency for a specific system is the key to proper temperature, and the maximum internal dissipation,
power supply design. For a 2.8-W audio system with the maximum ambient temperature can be calculated
4-Ω loads and a 5-V supply, the maximum draw on with Equation 18. The maximum recommended
the power supply is almost 3.8 W. junction temperature for the TPA6211A1 is 150°C.
A final point to remember about Class-AB amplifiers
is how to manipulate the terms in the efficiency
(18)
equation to the utmost advantage when possible.
Note that in Equation 15, V
DD
is in the denominator.
Equation 18 shows that the maximum ambient
This indicates that as V
DD
goes down, efficiency goes
temperature is 91.7°C (package limited to 85°C
up.
ambient) at maximum power dissipation with a 5-V
supply.
A simple formula for calculating the maximum power
dissipated, P
Dmax
, may be used for a differential
Table 2 shows that for most applications no airflow is
output application:
required to keep junction temperatures in the
specified range. The TPA6211A1 is designed with
thermal protection that turns the device off when the
junction temperature surpasses 150°C to prevent
(16)
damage to the IC. In addition, using speakers with an
P
Dmax
for a 5-V, 4-Ω system is 1.27 W.
impedance higher than 4-Ω dramatically increases
the thermal performance by reducing the output
current.
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