Θ
JA
+
1
Derating Factor
+
1
0.0088
+ 113
°C W
(9)
hBTL +
p
2 P
L
R
L
4 V
DD
Therefore,
(7)
T
A Max + TJ Max * ΘJA PDmax
+ 125 * 113(0.634) + 53.3°C
(10)
PCB LAYOUT
P
D max +
2 V2
D D
p 2
R
L
(8)
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-
BTL
Systems
TPA6203A1 is 125°C.
Power
Max
Output
Internal
Efficiency
From
Ambient
Power
Dissipation
(%)
Supply
Temperature
(W)
(°C)
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
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-
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-
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
laminate.
Increased
copper
also
increases
the
This indicates that as VDD 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, PDmax, 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
PDmax for a 5-V, 8- 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:
14
Copyright 2002–2008, Texas Instruments Incorporated