Datasheet

T = T + P
HOT_SPOT A DIS JA
· q
TPS65251
www.ti.com SLVSAA4D –JUNE 2010–REVISED DECEMBER 2012
Power Dissipation
The total power dissipation inside TPS65251 should not to exceed the maximum allowable junction temperature
of 125°C. The maximum allowable power dissipation is a function of the thermal resistance of the package (R
JA
)
and ambient temperature.
To calculate the temperature inside the device under continuous loading use the following procedure.
1. Define the set voltage for each converter.
2. Define the continuous loading on each converter. Make sure do not exceed the converter maximum loading.
3. Determine from the graphs below the expected losses (Y axis) in watts per converter inside the device. The
losses depend on the input supply, the selected switching frequency, the output voltage and the converter
chosen.
4. To calculate the maximum temperature inside the IC use the following formula:
(4)
Where:
T
A
is the ambient temperature
P
DIS
is the sum of losses in all converters
θ
JA
is the junction to ambient thermal impedance of the device and it is heavily dependant on board layout
BUCK 1 LOSSES (W) BUCK 1 LOSSES (W)
vs vs
OUTPUT CURRENT OUTPUT CURRENT
V
IN
= 12 V, f
SW
= 500 kHz V
IN
= 12 V, f
SW
= 1.1 MHz
V
O
(From Top to Bottom) = 5 V , 3.3 V, 2.5 V, 1.8 V, 1.2 V V
O
(From Top to Bottom) = 5 V , 3.3 V, 2.5 V, 1.8 V, 1.2 V
Figure 27. Figure 28.
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