ADP3339AKC-18 Analog Devices, ADP3339AKC-18 Datasheet - Page 7

• Manufacturer Part Number: ADP3339AKC-18
• Description: High-Accuracy Ultralow IQ/ 1.5 A/ anyCAP Low Dropout Regulator
• Manufacturer: Analog Devices

CALCULATING POWER DISSIPATION
Device power dissipation is calculated as follows:
Where I
and V
Assuming worst-case operating conditions are I
I
dissipation is:
So, for a maximum junction temperature of 125°C and a
maximum ambient temperature of 85°C, the required ther-
mal resistance from junction to ambient is:
PRINTED CIRCUIT BOARD LAYOUT
CONSIDERATIONS
The SOT-223’s thermal resistance, θ
sum of the junction-to-case and the case-to-ambient thermal
resistances. The junction-to-case thermal resistance, θ
determined by the package design and specified at 26.8°C/W.
However, the case-to-ambient thermal resistance is determined
by the printed circuit board design.
As shown in Figures 4a–4c, the amount of copper to which the
ADP3339 is mounted affects the thermal performance. When
mounted to just the minimal pads of 2 oz. copper (Figure 4a),
the θ
ADP3339 (Figure 4b), reduces the θ
the copper pad to 1 square inch (Figure 4c), reduces the θ
even further to 52.8°C/W.
GND
P
D
JA
= 14 mA, V
OUT
=
is 126.6°C/W. By adding a small copper pad under the
LOAD
(
3 3
are the input and output voltages respectively.
.
P
V
and I
D
– .
θ
=
2 5
JA
IN
(
V
GND
= 3.3 V, and V
IN
=
V
125
−
)
are load current and ground current, V
1500
V
1 246
° −
OUT
.
C
mA
)
W
85
×
I
°
+
LOAD
C
OUT
(
JA
3 3
=
JA
.
to 102.9°C/W. Increasing
= 2.5 V, the device power
32 1
+
, is determined by the
V
( )
.
V
)
14
IN
°
C W
mA
/
×
LOAD
I
GND
=
1246
= 1.5 A,
JC
, is
mW
JA
IN
Use the following general guidelines when designing printed
circuit boards:
1. Keep the output capacitor as close to the output and ground
2. Keep the input capacitor as close to the input and ground
3. PC board traces with larger cross sectional areas will remove
4. The thermal resistance can be decreased by adding a copper
5. If possible, utilize the adjacent area to add more copper
6. Use additional copper layers or planes to reduce the thermal
pins as possible.
pins as possible.
more heat from the ADP3339. For optimum heat transfer,
specify thick copper and use wide traces.
pad under the ADP3339 as shown in Figure 4b.
around the ADP3339. Connecting the copper area to the
output of the ADP3339, as shown in Figure 4c, is best but
will improve thermal performance even if it is connected to
other pins.
resistance. Again, connecting the other layers to the output
of the ADP3339 is best, but not necessary. When connecting
the output pad to other layers use multiple vias.
a.
b.
ADP3339
c.