1A Low-Voltage Low-Dropout Regulator
LM37101/37102
application. With respect to the applied package, the maximum output current of 1A may be still undeliverable
due to the restriction of the power dissipation of LM37101/2. 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
LM37101/2 is available in SOP-8 package. 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 130°C/W for SOP-8
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
Characteristic
Thermal Resistance Junction-To-Ambient / SOP-8
Thermal Resistance Junction-To-Ambient / TO-252
Symbol
θ
JA-SOP-8
θ
JA-TO-252
Rating
130
95
Unit
°C/W
°C/W
No heat sink / No air flow / No adjacent heat source / 20 mm
2
copper area. (T
A
=25°C)
Nov. 2011 – R1.1
-
10
-
HTC
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
