LM39300 Ver la hoja de datos (PDF) - Unspecified
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LM39300 Datasheet PDF : 12 Pages
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3A Low-Voltage Low-Dropout Regulator LM39300/39301/39302
Where TJ is the junction temperature, TC is the case temperature, TA is the ambient temperature, PD is the total
power dissipation of the device, θCA is the thermal resistance of case-to-ambient, θJC is the thermal resistance
of junction-to-case, and θJA is the thermal resistance of junction to ambient. The total power dissipation of the
device is given by:
PD = PIN – POUT = (VIN X IIN)–(VOUT X IOUT)
= (VIN X (IOUT+IGND)) – (VOUT X IOUT) = (VIN - VOUT) X IOUT + VIN X IGND
Where IGND is the operating ground current of the device which is specified at the Electrical Characteristics.
The maximum allowable temperature rise (TRmax) depends on the maximum ambient temperature (TAmax) of
the application, and the maximum allowable junction temperature (TJmax):
TRmax = TJmax – TAmax
The maximum allowable value for junction-to-ambient thermal resistance, θJA, can be calculated using the
formula:
θJA = TRmax / PD = (TJmax – TAmax) / PD
LM39300/1/2 is available in TO-263 and TO-220 package. The thermal resistance depends on amount of
copper area or heat sink, and on air flow. If the maximum allowable value of θJA calculated above is over
80°C/W for TO-263 package, 70°C/W for TO-220 package, no heat sink is needed since the package can
dissipate enough heat to satisfy these requirements. If the value for allowable θJA falls near or below these
limits, a heat sink or proper area of copper plane is required. In summary, the absolute maximum ratings of
thermal resistances are as follow:
Absolute Maximum Ratings of Thermal Resistance
Characteristic
Symbol
Rating
Thermal Resistance Junction-To-Ambient / TO-263
θJA-TO-263
80
Thermal Resistance Junction-To-Ambient / TO-220
θJA-TO-220
70
No heat sink / No air flow / No adjacent heat source / 20 mm2 copper area. (TA=25°C)
Unit
°C/W
°C/W
Feb. 2011 - Rev. 1.1
- 12 -
HTC
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