Datasheet

ADP1715/ADP1716
Rev. 0 | Page 13 of 20
should be aware of the parameters that contribute to 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 used
and the amount of copper to which the GND pins of the package
are soldered to on the PCB.
Table 5 shows typical θ
JA
values of the
8-lead thermally enhanced MSOP package for various PCB
copper sizes.
Table 5.
Copper Size (mm
2
)
θ
JA
(°C/W)
0
1
118
100 99
300 77
500 75
700 74
1
Device soldered to minimum size pin traces.
The junction temperature of the ADP1715/ADP1716 can be
calculated from the following equation:
T
J
= T
A
+ (P
D
× θ
JA
) (3)
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
) (4)
where:
I
LOAD
is the load current.
I
GND
is 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
} (5)
As shown in Equation 5, 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 the junction temperature does not rise above 125°C. The
following figures show junction temperature calculations for
different ambient temperatures, load currents, V
IN
to V
OUT
differentials, and areas of PCB copper.
140
0
05
06110-022
V
IN
– V
OUT
(V)
T
J
(°C)
120
100
80
60
40
20
1234
1mA
10mA
50mA
100mA
250mA
360mA
500mA
(LOAD CURRENT)
DO NOT OPERATE ABOVE THIS POINT
MAX T
J
Figure 34. 700 mm
2
of PCB Copper, T
A
= 25°C
140
0
05
06110-023
V
IN
– V
OUT
(V)
T
J
(°C)
120
100
80
60
40
20
1234
1mA
10mA
50mA
100mA
250mA
360mA
500mA
(LOAD CURRENT)
DO NOT OPERATE ABOVE THIS POINT
MAX T
J
Figure 35. 300 mm
2
of PCB Copper, T
A
= 25°C
140
0
05
06110-024
V
IN
– V
OUT
(V)
T
J
(°C)
120
100
80
60
40
20
1234
1mA
10mA
50mA
100mA
250mA
360mA
500mA
(LOAD CURRENT)
DO NOT OPERATE ABOVE THIS POINT
MAX T
J
Figure 36. 100 mm
2
of PCB Copper, T
A
= 25°C