LM10503 Datasheet, PDF (33/43 Pages) Texas Instruments – LM10503 Triple Buck Converter Energy Management Unit (EMU) with PowerWise® 2.0 Adaptive Voltage Scaling (AVS) and ADC

Thermal Considerations
The thermal characteristics of the device are specified using
the parameter θ_JA, which relates the junction temperature to
the ambient temperature. Although the value of θ_JA is depen-
dent on many variables, it still can be used to approximate the
operating junction temperature of the device. To obtain an
estimate of the device junction temperature, one may use the
following relationship:
T_J = P_D x θ_JA + T_A where:
P_D is the total power dissipation of the device;
T_J is the junction temperature in °C;
 θ_JA is the junction-to-ambient thermal resistance for the de-
vice;
T_A is the ambient temperature in °C.
It is important to always keep the operating junction temper-
ature (T_J) below 105°C for reliable operation. If the junction
temperature exceeds 160°C the device will cycle in and out
of thermal shutdown. If thermal shutdown occurs it is a sign
of inadequate heat sinking or excessive power dissipation in
the device.
The figure below provides a better approximation of the θ_JA
for a given PCB copper area. The PCB heatsink area consists
of 2oz. copper located on the bottom layer of the PCB directly
under the exposed pad. The bottom copper area is connected
to the exposed pad by means of a 4 x 4 array of 12 mil thermal
vias.
30112145
FIGURE 15. Thermal Resistance vs. PCB Area
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