1.5A Ultra Low Dropout Linear Regulator
TJ3965
Oct. 2006 – R1.2.1
9/9
HTC
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:
θ
JA = TRmax / PD
TJ3965 is available in SOT223, MSOP8, SOP8-PP, TO263, and TO220 packages.
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 140°C/W for SO-223 package, over 220°C/W for MSOP8 package,
over 165°C/W for SOP8 package, over 170°C/W for SOP8-PP package, over 80 °C/W for TO263
package, over 75 °C/W for TO220 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
No heat sink / No air flow / No adjacent heat source / TA = 25°C
Characteristic
Symbol
Max. Rating
Unit
Thermal Resistance Junction-To-Ambient / SOT223
θ
JA-SOT223
140
°C/W
Thermal Resistance Junction-To-Ambient / MSOP8
θ
JA-MSOP8
220
°C/W
Thermal Resistance Junction-To-Ambient / SOP8
θ
JA-SOP8
165
°C/W
Thermal Resistance Junction-To-Ambient / SOP8-PP
θ
JA-SOP8-PP
175
°C/W
Thermal Resistance Junction-To-Ambient / TO263
θ
JA-TO263
80
°C/W
Thermal Resistance Junction-To-Ambient / TO220
θ
JA-TO220
75
°C/W
T.B.D.