
1.5A Ultra Low Dropout Linear Regulator TJ3965
Oct. 2006 – R1.2.1
9/9
HTC
resistance of junction-to-case, and
θ
JA
is the thermal resistance of junction to ambient.
The total power dissipation of the device is given by:
P
D
= P
IN
– P
OUT
= (V
IN
X I
IN
)–(V
OUT
X I
OUT
)
= (V
IN
X (I
OUT
+I
GND
)) – (V
OUT
X I
OUT
) = (V
IN
- V
OUT
) X I
OUT
+ V
IN
X I
GND
where I
GND
is the operating ground current of the device which is specified at the Electrical Characteristics.
The maximum allowable temperature rise (T
Rmax
) depends on the maximum ambient temperature (T
Amax
)
of the application, and the maximum allowable junction temperature (T
Jmax
):
T
Rmax
= T
Jmax
– T
Amax
The maximum allowable value for junction-to-ambient thermal resistance,
θ
JA
, can be calculated using the
formula:
θ
JA
= T
Rmax
/ P
D
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
θ
JA
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
θ
JA
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 / T
A
= 25°C
Characteristic
Symbol
Max. Rating
Unit
Thermal Resistance Junction-To-Ambient / SOT223
θ
JA-SOT223
θ
JA-MSOP8
θ
JA-SOP8
θ
JA-SOP8-PP
θ
JA-TO263
θ
JA-TO220
140
°C/W
Thermal Resistance Junction-To-Ambient / MSOP8
220
°C/W
Thermal Resistance Junction-To-Ambient / SOP8
165
°C/W
Thermal Resistance Junction-To-Ambient / SOP8-PP
175
°C/W
Thermal Resistance Junction-To-Ambient / TO263
80
°C/W
Thermal Resistance Junction-To-Ambient / TO220
75
°C/W
T.B.D.