5
Board Layout
Board Layout
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This means that the total power dissipation of the TPS79801 must be less than 0.952 W. Now the input
voltage can be calculated.
P
d
= (V
in
– V
out
)
×
I
out
= (Vin – 3.3 V)
×
0.05 A = 0.952 W
(4)
So, the maximum input voltage needs to be 22.3 V or less in order to maintain a safe junction
temperature.
Similar analysis 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 answer
depends on the output voltage.
Output Voltage
Maximum Input Voltage
12
59.6
5
52.6
3.3
50.9
2.5
50.1
This section provides the TPS79801DCQEVM-434 board layout and illustrations.
Figure 1. Top Layer Assembly
4
TPS79801DCQEVM-434
SLUU346 – June 2009
