Datasheet

Data Sheet ADP1740/ADP1741
Rev. F | Page 17 of 20
In cases where the board temperature is known, the thermal
characterization parameter, Ψ
JB
, can be used to estimate the
junction temperature rise. Maximum junction temperature (T
J
)
is calculated from the board temperature (T
B
) and the power
dissipation (P
D
) using the following formula:
T
J
= T
B
+ (P
D
× Ψ
JB
) (7)
Figure 42 through Figure 45 show junction temperature
calculations for different board 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 = 10mA
LOAD = 100mA
LOAD = 250mA
LOAD = 500mA
LOAD = 1A
LOAD = 2A
07081-040
Figure 42. 500 mm
2
of PCB Copper, T
B
= 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 = 10mA
LOAD = 100mA
LOAD = 250mA
LOAD = 500mA
LOAD = 1A
LOAD = 2A
07081-041
Figure 43. 500 mm
2
of PCB Copper, T
B
= 50°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 = 10mA
LOAD = 250mA
LOAD = 500mA
LOAD = 1A
LOAD = 2A
LOAD = 100mA
07081-042
Figure 44. 1000 mm
2
of PCB Copper, T
B
= 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 = 10mA
LOAD = 250mA
LOAD = 500mA
LOAD = 1A
LOAD = 100mA
07081-043
LOAD = 2A
Figure 45. 1000 mm
2
of PCB Copper, T
B
= 50°C, LFCSP
PCB LAYOUT CONSIDERATIONS
Heat dissipation from the package can be improved by increasing
the amount of copper attached to the pins of the ADP1740/
ADP1741. However, as shown in Table 6, a point of diminishing
returns is eventually reached, beyond which an increase in the
copper size does not yield significant heat dissipation benefits.
Here are a few general tips when designing PCBs:
 Place the input capacitor as close as possible to the VIN
and GND pins.
 Place the output capacitor as close as possible to the VOUT
and GND pins.
 Place the soft start capacitor close to the SS pin.
 Connect the load as close as possible to the VOUT and
SENSE pins (ADP1740) or to the VOUT and ADJ pins
(ADP1741).
Use of 0603 or 0805 size capacitors and resistors achieves the
smallest possible footprint solution on boards where area is
limited.