Datasheet

Θ
JA
+
1
Derating Factor
+
1
0.0088
+ 113°CńW
(9)
h
BTL
+
p 2 P
L
R
L
Ǹ
4 V
DD
Therefore,
(7)
T
A
Max + T
J
Max * Θ
JA
P
Dmax
+ 125 * 113
(
0.634
)
+ 53.3°C
(10)
PCB LAYOUT
P
D max
+
2 V
2
DD
p
2
R
L
(8)
TPA6203A1
SLOS364F – MARCH 2002 – REVISED JUNE 2008 .......................................................................................................................................................... www.ti.com
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
Table 2. Efficiency and Maximum Ambient
recommended junction temperature for the
Temperature vs Output Power in 5-V 8- Ω BTL
Systems TPA6203A1 is 125 ° C.
Power Max
Output Internal
Efficiency From Ambient
Power Dissipation
(%) Supply Temperature
(W) (W)
(W) ( ° C)
Equation 10 shows that the maximum ambient
0.25 31.4 0.55 0.75 62
temperature is 53.3 ° C at maximum power dissipation
0.50 44.4 0.62 1.12 54
with a 5-V supply.
1.00 62.8 0.59 1.59 58
Table 2 shows that for most applications no airflow is
1.25 70.2 0.53 1.78 65
required to keep junction temperatures in the
specified range. The TPA6203A1 is designed with
Table 2 employs Equation 7 to calculate efficiencies
thermal protection that turns the device off when the
for four different output power levels. Note that the
junction temperature surpasses 150 ° C to prevent
efficiency of the amplifier is quite low for lower power
damage to the IC. Also, using more resistive than 8- Ω
levels and rises sharply as power to the load is
speakers dramatically increases the thermal
increased resulting in a nearly flat internal power
performance by reducing the output current.
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
In making the pad size for the BGA balls, it is
power supply design. For a 1.25-W audio system with
recommended that the layout use solder-
8- Ω loads and a 5-V supply, the maximum draw on
mask-defined (SMD) land. With this method, the
the power supply is almost 1.8 W.
copper pad is made larger than the desired land area,
and the opening size is defined by the opening in the
A final point to remember about Class-AB amplifiers
solder mask material. The advantages normally
is how to manipulate the terms in the efficiency
associated with this technique include more closely
equation to the utmost advantage when possible.
controlled size and better copper adhesion to the
Note that in Equation 7 , V
DD
is in the denominator.
laminate. Increased copper also increases the
This indicates that as V
DD
goes down, efficiency goes
thermal performance of the IC. Better size control is
up.
the result of photo imaging the stencils for masks.
A simple formula for calculating the maximum power
Small plated vias should be placed near the center
dissipated, P
Dmax
, may be used for a differential
ball connecting ball B2 to the ground plane. Added
output application:
plated vias and ground plane act as a heatsink and
increase the thermal performance of the device.
Figure 34 shows the appropriate diameters for a 2
mm X 2 mm MicroStar Junior™ BGA layout.
It is very important to keep the TPA6203A1 external
P
Dmax
for a 5-V, 8- Ω system is 634 mW.
components very close to the TPA6203A1 to limit
The maximum ambient temperature depends on the
noise pickup. The TPA6203A1 evaluation module
heat sinking ability of the PCB system. The derating
(EVM) layout is shown in the next section as a layout
factor for the 2 mm x 2 mm Microstar Junior™
example.
package is shown in the dissipation rating table.
Converting this to θ
JA
:
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