Datasheet

ADP150 Data Sheet
Rev. B | Page 14 of 20
THERMAL CONSIDERATIONS
In most applications, the ADP150 does not dissipate much heat
due to its high efficiency. However, in applications with high
ambient temperature and high supply voltage to output voltage
differential, the heat dissipated in the package is large enough
that it can cause the junction temperature of the die to exceed
the maximum junction temperature of 125°C.
When the junction temperature exceeds 150°C, the converter
enters thermal shutdown. It recovers only after the junction
temperature decreases below 135°C to prevent any permanent
damage. Therefore, thermal analysis for the chosen application is
very important to guarantee reliable performance over 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 ADP150 must not exceed 125°C. To ensure that the junction
temperature stays below 125°C, be aware of the parameters that
contribute to the junction temperature changes. These parameters
include ambient temperature, power dissipation in the power
device, and thermal resistances 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 copper
used to solder the package GND pins to the PCB. Table 7 shows
typical θ
JA
values of the 5-lead TSOT and 4-ball WLCSP packages
for various PCB copper sizes. Table 8 shows the typical Ψ
JB
value of the 5-lead TSOT and 4-b a l l W L C S P.
Table 7. Typical θJA Values
θ
JA
(°C/W)
Copper Size (mm
2
) TSOT WLCSP
0
1
170 260
50 152 159
100 146 157
300 134 153
500 131 151
1
Device soldered to minimum size pin traces.
Table 8. Typical Ψ
JB
Values
Ψ
JB
(°C/W)
TSOT WLCSP
42.8 58.4
Use Equation 2 to calculate the junction temperature.
T
J
= T
A
+ (P
D
× θ
JA
) (2)
where:
T
A
is the ambient temperature.
P
D
is the power dissipation in the die, given by
P
D
= [(V
IN
− V
OUT
) × I
LOAD
] + (V
IN
× I
GND
)
where:
I
LOAD
is the load current.
I
GND
is the ground current.
V
IN
and V
OUT
are input and output voltages, respectively.
Power dissipation due to ground current is quite small and can be
ignored. Therefore, the junction temperature equation simplifies to
T
J
= T
A
+ {[(V
IN
− V
OUT
) × I
LOAD
] × θ
JA
} (3)
As shown in the previous equation, for a given ambient temperature,
input-to-output voltage differential, and continuous load current,
there exists a minimum copper size requirement for the PCB to
ensure that the junction temperature does not rise above 125°C.
Figure 33 to Figure 46 show the junction temperature calculations
for the different ambient temperatures, load currents, V
IN
-to-V
OUT
differentials, and areas of PCB copper.
140
120
100
80
60
40
20
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
V
IN
– V
OUT
(V)
JUNCTION TEMPERATURE, T
J
(°C)
I
LOAD
= 1mA
I
LOAD
= 10mA
I
LOAD
= 25mA
I
LOAD
= 50mA
I
LOAD
= 75mA
I
LOAD
= 100mA
I
LOAD
= 150mA
MAX JUNCTION TEMPERATURE
08343-228
Figure 33. TSOT, 500 mm
2
of PCB Copper, T
A
= 25°C
140
120
100
80
60
40
20
0
0.5 1.0 1.5 2.0 2.5
3.0 3.5 4.0 4.5
V
IN
– V
OUT
(V)
JUNCTION TEMPERATURE, T
J
(°C)
I
LOAD
= 1mA
I
LOAD
= 10mA
I
LOAD
= 25mA
I
LOAD
= 50mA
I
LOAD
= 75mA
I
LOAD
= 100mA
I
LOAD
= 150mA
MAX JUNCTION TEMPERATURE
08343-229
Figure 34. TSOT, 100 mm
2
of PCB Copper, T
A
= 25°C