1.5A Ultra Low Dropout Linear Regulator
TJ3965
VOUT
R2
ADJ
GND
R1
+
22µF
-
OUTPUT
VOUT
R2
ADJ
GND
R1
10µF
OUTPUT
Additional Resistance
Maximum Output Current Capability
The TJ3965 can deliver a continuous current of 1.5A over the full operating junction temperature range.
However, the output current is limited by the restriction of power dissipation which differs from packages.
A heat sink may be required depending on the maximum power dissipation and maximum ambient
temperature of application. With respect to the applied package, the maximum output current of 1.5A
may be still undeliverable due to the restriction of the power dissipation of TJ3965. Under all possible
conditions, the junction temperature must be within the range specified under operating conditions.
The temperatures over the device are given by:
T
C
= T
A
+ P
D
X
θ
CA
/ T
J
= T
C
+ P
D
X
θ
JC
/ T
J
= T
A
+ P
D
X
θ
JA
where T
J
is the junction temperature, T
C
is the case temperature, T
A
is the ambient temperature, P
D
is the
total power dissipation of the device,
θ
CA
is the thermal resistance of case-to-ambient,
θ
JC
is the thermal
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
= (T
Jmax
– T
Amax
) / P
D
TJ3965 is available in SOT223, MSOP8, SOP8-PP, TO263, TO220, and SOT89 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 SOT223 package, over 220°C/W for MSOP8 package,
over 165°C/W for SOP8 package, over 175°C/W for SOP8-PP package, over 105 °C/W for TO252
package, over 80 °C/W for TO263 package, over 70 °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°
Jul. 2010 – Rev. 1.12
-
10
-
HTC
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
