ADP1720-EP Datasheet, PDF (10/12 Pages) Analog Devices – 50 mA, High Voltage, Micropower Linear Regulator

ADP1720-EP
APPLICATIONS INFORMATION
THERMAL CONSIDERATIONS
To guarantee reliable operation, the junction temperature of
the ADP1720-EP must not exceed 125°C. To ensure that the
junction temperature stays below this maximum value, the user
needs to be aware of the parameters that contribute to junction
temperature changes. These parameters include ambient tempera-
ture, 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 on the PCB. Table 5 shows typical θ_JA values of the
8-lead MSOP package for various PCB copper sizes.
Table 5. Typical θ_JA Values for ADP1720-EP
Copper Size (mm²)
θ_JA (°C/W)
25
246
50
216
100
186
300
178
500
169
The junction temperature of the ADP1720-EP 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 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}
(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 that the junction temperature does not rise
above 125°C. Figure 19 to Figure 24 show junction temperature
calculations for different ambient temperatures, load currents,
V_IN to V_OUT differentials, and areas of PCB copper for the
ADP1720-EP.
Data Sheet
140
MAX T_J (DO NOT OPERATE ABOVE THIS POINT)
120
100
80
60
40
20
1mA
5mA
0
0
4
10mA
20mA
8
12
30mA
40mA
16
50mA
(LOAD CURRENT)
20
24
28
V_IN – V_OUT (V)
Figure 19. 500 mm² of PCB Copper, T_A = 25°C
140
MAX T_J (DO NOT OPERATE ABOVE THIS POINT)
120
100
80
60
40
20
1mA
5mA
0
0
4
10mA
20mA
8
12
30mA
40mA
16
50mA
(LOAD CURRENT)
20
24
28
V_IN – V_OUT (V)
Figure 20. 300 mm² of PCB Copper, T_A = 25°C
140
MAX T_J (DO NOT OPERATE ABOVE THIS POINT)
120
100
80
60
40
20
1mA
5mA
0
0
4
10mA
20mA
8
12
30mA
40mA
16
50mA
(LOAD CURRENT)
20
24
28
V_IN – V_OUT (V)
Figure 21. 100 mm² of PCB Copper, T_A = 25°C
Rev. A | Page 10 of 12