LM1084
THERMAL CONSIDERATIONS
The
LM1084
series have internal power and thermal limiting circuitry designed to protect the device under overload
conditions. However maximum junction temperature ratings should not be exceeded under continuous normal load
conditions.
Careful consideration must be given to all sources of thermal resistance from junction to ambient, including junction-to-case,
case-to-heat sink interface and heat sink resistance itself. To ensure safe operating temperatures and reflect more
accurately the device temperature, new thermal resistance specifications have been developed. Unlike older regulators with
a single junction-to-case thermal resistance specification, the data section for these new regulators provides a separate
thermal resistance and maximum junction temperature for both the Control Section and the Power Transistor. Calculations
for both temperatures under certain conditions of ambient temperature and heat sink resistance and to ensure that both
thermal limits are met.
Junction-to-case thermal resistance is specified from the IC junction to the bottom of the case directly below the die. This is
the lowest resistance path for the heat flow. In order to ensure the best possible thermal flow from this area of the package
to the heat sink proper mounting is required. Thermal compound at the case-to-heat sink interface is recommended. A
thermally conductive spacer can be used, if the case of the device must be electrically isolated, but its added contribution to
thermal resistance has to be considered.
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