Datasheet

EVAL-ADP1752/ADP1753
Rev. 0 | Page 8 of 12
The junction temperature of the ADP1752/ADP1753 can be
calculated from the following equation:
T
J
= T
A
+ (P
D
× θ
JA
) (1)
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
) (2)
where:
V
IN
and V
OUT
are the input and output voltages, respectively.
I
LOAD
is the load current.
I
GND
is the ground current.
Power dissipation due to ground current is quite small and can
be ignored. Therefore, the junction temperature equation can
be simplified as follows:
T
J
= T
A
+ {[(V
IN
− V
OUT
) × I
LOAD
] × θ
JA
} (3)
As shown in Equation 3, for a given ambient temperature, input-
to-output voltage differential, and continuous load current, a
minimum copper size requirement exists for the PCB to ensure
that the junction temperature does not rise above 125°C. Figure 11
thr
ough Figure 16 show junction temperature calculations for
different ambient temperatures, load currents, V
IN
to V
OUT
differentials, and areas of PCB copper.
140
120
100
80
60
40
20
0
0.25 0.75 1.25 1.75 2.25 2.75
JUNCTION TEMPERATURE, T
J
(°C)
V
IN
– V
OUT
(V)
MAX JUNCTION
TEMPERATURE
LOAD = 800mA
LOAD = 100mA
LOAD = 50mA
LOAD = 10mA
LOAD = 400mA
LOAD = 200mA
07739-135
Figure 11. 6400 mm
2
of PCB Copper, T
A
= 25°C, LFCSP
140
120
100
80
60
40
20
0
0.25 0.75 1.25 1.75 2.25 2.75
JUNCTION TEMPERATURE, T
J
(°C)
V
IN
– V
OUT
(V)
MAX JUNCTION
TEMPERATURE
LOAD = 800mA
LOAD = 100mA
LOAD = 50mA
LOAD = 10mA
LOAD = 400mA
LOAD = 200mA
07739-136
Figure 12. 500 mm
2
of PCB Copper, T
A
= 25°C, LFCSP
140
120
100
80
60
40
20
0
0.25 0.75 1.25 1.75 2.25 2.75
JUNCTION TEMPERATURE, T
J
(°C)
V
IN
– V
OUT
(V)
MAX JUNCTION
TEMPERATURE
LOAD = 800mA
LOAD = 100mA
LOAD = 50mA
LOAD = 10mA
LOAD = 400mA
LOAD = 200mA
07739-137
Figure 13. 0 mm
2
of PCB Copper, T
A
= 25°C, LFCSP
140
120
100
80
60
40
20
0
0.25 0.75 1.25 1.75 2.25 2.75
JUNCTION TEMPERATURE, T
J
(°C)
V
IN
– V
OUT
(V)
MAX JUNCTION
TEMPERATURE
LOAD = 800mA
LOAD = 100mA
LOAD = 50mA
LOAD = 10mA
LOAD = 400mA
LOAD = 200mA
07739-138
Figure 14. 6400 mm
2
of PCB Copper, T
A
= 50°C, LFCSP