Datasheet

Data Sheet ADP2370/ADP2371
Rev. C | Page 29 of 32
THERMAL CONSIDERATIONS
In most applications, the ADP2370/ADP2371 do not dissipate
much heat due to their high efficiency. However, in applications
with high ambient temperature and high supply voltage-to-output
voltage differential, the heat dissipated in the package may be
large enough to cause the junction temperature of the die to
exceed the 125°C maximum.
If the junction temperature of the ADP2370/ADP2371 exceeds
150°C, the regulator enters thermal shutdown. The regulator
recovers only after the junction temperature has fallen below
130°C, this helps to prevent any permanent damage to the IC.
Thermal analysis for the chosen application is clearly very
important to guarantee reliable operation under all conditions.
The junction temperature of the die is the sum of the ambient
temperature of the environment and the temperature rise of the
package due to the power dissipation, as shown in Equation 2.
To guarantee reliable operation, the junction temperature of the
ADP2370/ADP2371 must not exceed 125°C. To ensure the junc-
tion temperature stays below this maximum value, the user must
be aware of the parameters that contribute to junction temperature
changes. These parameters include ambient temperature, power
dissipation in the power device, and the thermal resistance between
the junction and ambient air (θ
JA
). The θ
JA
number is dependent
on the package assembly compounds that are used and the amount
of PCB copper soldered to the package GND and EPA D. Table 8
shows typical θ
JA
values of the 8-lead, 3 mm × 3 mm LFCSP for
various PCB copper sizes.
Table 8. Typical θ
JA
Values
Copper Size (mm
2
) θ
JA
(°C/W)
25
1
162.2
100 124.1
500 68.7
1000 56.5
6400 42.4
1
The device is soldered to minimum size pin traces.
The junction temperature of the ADP2370/ADP2371 is
calculated from the following equation:
T
J
= T
A
+ (P
D
× θ
JA
) (2)
where:
T
A
is the ambient temperature.
P
D
is the total power dissipation in the die, given by
P
D
= P
BUCK
= P
SW
+ P
TRAN
+ P
SW_COND
(3)
where:
P
SW
, P
TRAN
, and P
SW_COND
are defined in the Efficiency section.
For a given ambient temperature and total power dissipation,
there exists a minimum copper size requirement for the PCB to
ensure the junction temperature does not rise above 125°C. The
following figures (Figure 86 to Figure 89) show junction
temperature calculations for different ambient temperatures,
total power dissipation, and areas of PCB copper.
25
35
45
55
65
75
85
95
105
1
15
125
135
145
0 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50
JUNCTION TEMPERATURE (°C)
TOTAL POWER DISSIPATION (W)
6400mm
2
500mm
2
100mm
2
T
J
MAX
09531-086
Figure 86. Junction Temperature vs. Power Dissipation, T
A
= 25°C
0 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00
JUNCTION TEMPERATURE (°C)
TOTAL POWER DISSIPATION (W)
09531-087
50
60
70
80
90
100
110
120
130
140
6400mm
2
500mm
2
100mm
2
T
J
MAX
Figure 87. Junction Temperature vs. Power Dissipation, T
A
= 50°C
0 0.25 0.50 0.75 1.00
1.25
1.50 1.75
2.00
JUNCTION TEMPERATURE (°C)
TOTAL POWER DISSIPATION (W)
09531-088
6400mm
2
500mm
2
100mm
2
T
J
MAX
65
75
85
95
105
115
125
135
145
Figure 88. Junction Temperature vs. Power Dissipation, T
A
= 65°C