LP38869_15 Datasheet, PDF (15/23 Pages) Texas Instruments – 1A FlexCap, Low-Dropout Linear Regulator with 0.75% Accuracy

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LP38869
SNVS877B – AUGUST 2012 – REVISED APRIL 2013
Figure 35. Typical Soft-Start Current Limit Behavior with C_SS = 100 nF
Thermal Overload Protection
Thermal overload protection limits total power dissipation in the LP38869. When the junction temperature
exceeds typically T_J = +160°C, the thermal sensor turns off the pass transistor, allowing the LP38869 to cool.
The thermal sensor turns the pass transistor on once the IC’s junction temperature drops by approximately 15°C.
Continuous short-circuit conditions will eventually result in a pulsed output current with a frequency that depends
on the thermal resistance and thermal mass of the LP38869 package and PC board combination as well as the
ambient temperature. Thermal overload protection is designed to protect the LP38869 in the event of fault
conditions. For continuous operation, do not exceed the absolute maximum junction temperature rating of T_J =
150°C. Parametric ratings are not ensured if the junction rises above 125°C.
Operating Region and Power Dissipation
Maximum power dissipation of the LP38869 depends on the thermal resistance of the case and circuit board, the
temperature difference between the die junction and ambient air, and the rate of air flow. The power dissipation
across the device is defined by:
P_DISS = I_OUT X (V_IN – V_OUT)
(9)
The resulting maximum power dissipation is:
P_DISS(MAX) = (T_J(MAX) - T_A(MAX)) / (θ_JA
(10)
Where (T_J(MAX) - T_A(MAX)) is the maximum allowable junction temperature rise above the surrounding ambient air;
and θ_JA is thermal resistance from the junction through the package DAP, to the PC board, copper traces, and
other materials into the surrounding air.
Figure 36 uses this formula to show a range of allowable dissipation values that will keep the junction
temperature (T_J(MAX)) inside the Maximum Operating Junction Temperature of 125°C.
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