Datasheet

Board Layout, Schematic, and Parts List www.ti.com
All temperatures are in degrees Celsius.
The measured thermal resistance from junction to ambient for the TPS73x01EVM has a typical value of
40°C/W. The recommended maximum operating junction temperature specified in the product data sheet
for the TPS73x01 family is +125°C. With these two pieces of information, the maximum power dissipation
can be found by using Equation (1).
Example 1. Sample Calculation
What is the maximum input voltage that can be applied to a TPS73701DRB with a 1.8-V output voltage if the
ambient temperature is +85°C and the full 1 A of load current is required?
Given:
T
J
= +125°C, T
A
= +85°C, θ
JA
= 40°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 W.
125°C = 85°C + P
D
(40°W/C)
This result means that the total power dissipation of the TPS73701DRB must be less than 1 W. Now the input
voltage can be calculated.
P
D
= (V
IN
– V
OUT
) × I
OUT
= (V
IN
– 1.8 V) × 1 A = 1 W
So the maximum input voltage would need to be 2.8 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)
or +85°C to provide full output current while maintaining the junction temperature at or below +125°C. The
answer depends on the desired output voltage, as Table 3 shows.
Table 3. Maximum Input Voltage
TPS73701DRB TPS73601DRB TPS73201DRB
Output
Ambient Temperature Ambient Temperature Ambient Temperature
Voltage
V
OUT
+25°C +85°C +25°C
(1)
+85°C +25°C
(1)
+85°C
(1)
1.8 V 4.3 V 2.8 V 5.5 V 4.3 V 5.5 V 5.5 V
2.5 V 5.0 V 3.5 V 5.5 V 5.0 V 5.5 V 5.5 V
2.8 V 5.3 V 3.8 V 5.5 V 5.3 V 5.5 V 5.5 V
3.0 V 5.5 V 4.0 V 5.5 V 5.5 V 5.5 V 5.5 V
3.3 V 5.5 V
(1)
4.3 V 5.5 V 5.5 V
(1)
5.5 V 5.5 V
(1)
Limited by recommended operating maximum temperature, not thermal resistance.
5 Board Layout, Schematic, and Parts List
This section provides the TPS73x01DRBEVM-518 board layout and illustrations. It also provides the
TPS73x01DRBEVM-518 schematic and bill of materials.
5.1 PCB Layout
Figure 1 through Figure 4 show the layout for the TPS73x01DRBEVM-518 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 TPS73x01DRBEVM-518 PCBs.
4
TPS73x01DRBEVM-518 SBVU014–August 2009
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