Datasheet
Board Layout
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For example, what is the maximum input voltage that can be applied to a TPS73401 with the output
voltage configured to 3.3V if the ambient temperature is 85°C and the full 250mA of load current is
required?
Given: T
J
= 125°C, T
A
= 85°C, θ
JA
= 38°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
=1.053W.
125°C=85°C + P
d
(38°C/W) (2)
This means that the total power dissipation of the TPS73401 must be less than 1.053W. Now the input
voltage can be calculated.
P
d
= (V
in
– V
out
) × I
out
= (Vin – 3.3V) × 0.25A = 1.053W (3)
So the maximum input voltage would need to be 7.51V or less in order to maintain a safe junction
temperature. But since the maximum recommended input voltage is 6.5V, the supply voltage is limited to
6.5V.
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 will
depend on the output voltage.
Table 2. Maximum Calculated Input Voltage
Maximum Calculated Input Voltage (V)
Output voltage
(V)
At Ambient Temperature = 25°C At Ambient Temperature = 85°C
1.5 12.03 (cannot exceed 6.5) 5.71
1.8 12.33 (cannot exceed 6.5) 6.01
2.8 13.33 (cannot exceed 6.5) 7.01 (cannot exceed 6.5)
3.3 13.83 (cannot exceed 6.5) 7.51 (cannot exceed 6.5)
5 Board Layout
This chapter provides the TPS73401DRVEVM-527 board layout and illustrations.
Figure 1. Top Layer Assembly
4
TPS73401DRV EVM SLVU333A–August 2009–Revised March 2012
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