LP38869 datasheet(15/23 Pages) TI

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LP38869

www.ti.com

SNVS877B – AUGUST 2012 – REVISED APRIL 2013

Figure 35. Typical Soft-Start Current Limit Behavior with CSS = 100 nF

Thermal Overload Protection

Thermal overload protection limits total power dissipation in the LP38869. When the junction temperature

exceeds typically TJ = +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 TJ =

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:

PDISS = IOUT X (VIN – VOUT)

(9)

The resulting maximum power dissipation is:

PDISS(MAX) = (TJ(MAX) - TA(MAX)) / (θJA

(10)

Where (TJ(MAX) - TA(MAX)) is the maximum allowable junction temperature rise above the surrounding ambient air;

and

θJA 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 (TJ(MAX)) inside the Maximum Operating Junction Temperature of 125°C.

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LP38869 Datasheet(PDF) 15 Page - Texas Instruments