LP3987
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 LP3987, 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 SOT-23-5 package is 250°C/W.
PD(MAX) = (125°C−25°C) / 250 = 400mW (SOT-23-5)
PD(MAX) = (125°C−25°C) / 165 = 606mW
The maximum power dissipation depends on
operating
ambient temperature for fixed TJ(MAX) and thermal
resistance
θJA
.
LP3987-datasheet
Oct.-2003
7-7
POWER [ LOWPOWER SEMICONDUCTOR INC ]
