Datasheet

EVAL-ADP1740/ADP1741
Rev. 0 | Page 7 of 12
PCB LAYOUT CONSIDERATIONS
Heat dissipation from the package can be improved by increase-
ing the amount of copper attached to the pins of the ADP1740/
ADP1741. However, as shown in Tabl e 2, 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.
07154-009
Figure 9. Typical Board Layout, Top Side
07154-010
Figure 10. Typical Board Layout, Bottom Side
THERMAL CONSIDERATIONS
To guarantee reliable operation, the junction temperature of the
ADP1740/ADP1741 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 temp-
erature, power dissipation in the power device, and thermal
resistance between the junction and ambient air (θ
JA
). The θ
JA
value is dependent on the package assembly compounds used
and the amount of copper to which the GND pins of the pack-
age are soldered on the PCB. Table 2 shows typical θ
JA
values of
the 16-lead LFCSP for various PCB copper sizes. Table 3 shows
the typical Ψ
JB
value of the 16-lead LFCSP.
Table 2. Typical θ
JA
Values
Copper Size (mm
2
) θ
JA
(°C/W), LFCSP
0
1
130
100 80
500 69
1000 54
6400 42
1
Device soldered to minimum size pin traces.
Table 3. Typical Ψ
JB
Values
Copper Size (mm
2
) Ψ
JB
(°C/W) @ 1 W
100 32.7
500 31.5
1000 25.5