Datasheet

+125 C=+85 C+P (315 C/W)
D
° ° °
(2)
P =(V V ) I =(-
D IN OUT
V 3.3V) 0.08A=0.126W
IN
-´ ´
OUT
(3)
5 Board Layout, Schematic, and Parts List
5.1 PCB Layouts
Board Layout, Schematic, and Parts List www.ti.com
Example 1. Maximum Power Dissipation Calculation
What is the maximum input voltage that can be applied to a TPS71401 with the output voltage
configured to 3.3 V if the ambient temperature is +85 ° C and the full 80 mA of load current is required?
Given:
T
J
= +125 ° C, T
A
= +85 ° C, θ
JA
= 315 ° C/W
Using Equation 1 , we substitute in the given values above and find that the maximum power dissipation
for the part is P
D
= 0.615 W.
This result means that the total power dissipation of the TPS71401 must be less than 0.126 W. Now the
input voltage can be calculated:
Therefore, the maximum input voltage should be 4.88 V or less in order to maintain a safe junction
temperature.
Similar analyses can be performed to determine the maximum input voltage at room temperature (+25 ° C)
to provide full output current while maintaining the junction temperature at or below +125 ° C. The
maximum input voltage depends on the output voltage. Table 3 lists the maximum input voltage allowed
for the pre-programmed output voltages.
Table 3. Maximum Input Voltage (V)
Maximum Input Voltage
Output Voltage (V) (V)
5.0 8.96
3.3 7.26
2.7 6.67
2.5 6.46
This section provides the TPS71401DCKEVM-425 board layout and illustrations. It also includes the
schematic and bill of materials for the EVM.
Figure 1 through Figure 3 show the layout for the TPS71401DCKEVM-425 PCB.
Note: Board layouts are not to scale. These figures are intended to show how the board is laid out;
they are not intended to be used for manufacturing TPS71401DCKEVM-425 PCBs.
4 TPS71401DCKEVM-425 SBVU012 – January 2009
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