LP3983S datasheet(7/8 Pages) POWER

7 / 8 page

LP3983S-06

May.-2017

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Page 7 of 8

Preliminary Datasheet

LP3983S

Thermal Considerations

Thermal protection limits power dissipation in

LP3983S. When the operation junction temperature

exceeds 150°C, the OTP circuit starts the thermal

shutdown function turn the pass element off. The

pass element turns on again after the junction

temperature cools by 25°C. For continue operation,

do not exceed absolute maximum operation junction

temperature 125°C.

The power dissipation definition in device is:

PD = (VIN−VOUT) x IOUT + VIN x IQ

The maximum power dissipation depends on the

thermal resistance of IC package, PCB layout, the

rate of surroundings airflow and temperature

difference between junction to ambient. The

maximum power dissipation can be calculated by

following formula:

PD(MAX) = ( TJ(MAX) − TA ) /θJA

Where TJ(MAX) is the maximum operation junction

temperature 125°C, TA is the ambient temperature

and the θJA is the junction to ambient thermal

resistance. For recommended operating conditions

specification of LP3983S, where TJ(MAX) is the

maximum junction temperature of the die (125°C)

and TA is the maximum ambient temperature. The

junction to ambient thermal resistance (θJA is layout

dependent) for SOT23-5 package is 195°C/W.

PD(MAX) = (125°C−25°C) /195 = 500mW

The maximum power dissipation depends on

operating ambient temperature for fixed TJ(MAX) and

thermal resistance θJA.

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