Datasheet
Data Sheet ADP222/ADP223/ADP224/ADP225
Rev. D | Page 21 of 24
The junction temperature of the ADP222/ADP223/ADP224/
ADP225 can be calculated by
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 the following:
T
J
= T
A
+ {[(V
IN
− V
OUT
) × I
LOAD
] × θ
JA
}
As shown in the simplified 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 72 to Figure 75 show junction temperature
calculations for different ambient temperatures, power dissipation,
and areas of PCB copper.
140
120
100
80
60
40
20
0
JUNCTION TEMPERATURE T
J
(°C)
TOTAL POWER DISSIPATION (W)
0 0.2 0.4 0.6 0.8 1.0 1.2
6400mm
2
1000mm
2
500mm
2
100mm
2
25mm
2
JEDEC
T
J
MAX
09376-048
Figure 72. 8-Lead LFCSP, T
A
= 25°C
140
120
100
80
60
40
20
0
JUNCTION TEMPERATURE T
J
(°C)
T
O
T
A
L
POWER DISSI
PATION (W)
0
0.2
0.4
0.6 0.8
1.0
1.2
6400mm
2
1000mm
2
500mm
2
100mm
2
25mm
2
JEDEC
T
J
MAX
09376-049
Figure 73. 8-Lead LFCSP, T
A
= 50°C
140
120
100
80
60
40
20
0
JUNCTION TEMPERATURE T
J
(°C)
TOTAL POWER DISSIPATION (W)
0 0.2 0.4 0.6 0.8 1.0 1.2
6400mm
2
1000mm
2
500mm
2
100mm
2
25mm
2
JEDEC
T
J
MAX
09376-050
Figure 74. 8-Lead LFCSP, T
A
= 85°C
140
120
100
80
60
40
20
0
JUNCTION TEMPERA
TURE T
J
(°C)
TOTA
L POWER DISSIPATION (W)
0
21
3
4 5
6 7
T
B
= 25°C
T
B
= 50°C
T
B
= 85°C
T
J
MAX
09376-051
Figure 75. 8-Lead LFCSP, T
A
= 85°C
In the case where the board temperature is known, use the
thermal characterization parameter, Ψ
JB
, to estimate the
junction temperature rise (see Figure 75). Maximum junction
temperature (T
J
) is calculated from the board temperature (T
B
)
and power dissipation (P
D
) using the following formula:
T
J
= T
B
+ (P
D
× Ψ
JB
) (3)
The typical value of Ψ
JB
is 18.2°C/W for the 8-lead LFCSP package.