ADP3338AKC-33 AD [Analog Devices], ADP3338AKC-33 Datasheet - Page 7

• Manufacturer Part Number: ADP3338AKC-33
• Description: High-Accuracy Ultralow IQ, 1 A, anyCAP Low Dropout Regulator
• Manufacturer: AD [Analog Devices]

THERMAL OVERLOAD PROTECTION
The ADP3338 is protected against damage due to excessive power
dissipation by its thermal overload protection circuit. Thermal
protection limits the die temperature to a maximum of 160°C.
Under extreme conditions (i.e., high ambient temperature and
power dissipation) where the die temperature starts to rise above
160°C, the output current will be reduced until the die tempera-
ture has dropped to a safe level.
Current and thermal limit protections are intended to protect
the device against accidental overload conditions. For normal
operation, the device’s power dissipation should be externally
limited so that the junction temperature will not exceed 150°C.
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 junction temperature of 125°C and a maximum ambi-
ent temperature of 85°C, the required thermal 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.
GND
P
D
= 10 mA, V
OUT
=
LOAD
(
3 3
are the input and output voltages respectively.
.
P
V
D
and I
=
– .
θ
IN
2 5
(
V
JA
GND
IN
= 3.3 V and V
=
V
−
125
are load current and ground current, V
)
V
1000
0 833
OUT
°
.
C
)
mA
–
×
W
85
I
LOAD
+
OUT
°
C
(
3 3
JA
=
.
= 2.5 V, the device power
+
, is determined by the
48
V
( )
V
)
°
IN
10
C W
/
×
mA
LOAD
I
GND
=
833
= 1.0 A,
JC
, is
mW
IN
As shown in Figures 4a–c, the amount of copper the ADP3338
is mounted to affects the thermal performance. When mounted
to 2 oz. copper with just the minimal pads, Figure 4a, the θ
126.6°C/W. By adding a small copper pad under the ADP3338,
Figure 4b, reduces the θ
pad to 1 square inch, Figure 4c, reduces the θ
to 52.8°C/W.
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 ADP3338. For optimum heat transfer,
specify thick copper and use wide traces.
pad under the ADP3338 as shown in Figure 4b.
around the ADP3338. Connecting the copper area to the
output of the ADP3338, as shown in Figure 4c, is best but
will improve thermal performance even if it is connected to
other signals.
resistance. Again, connecting the other layers to the output
of the ADP3338 is best, but not necessary. When connecting
the output pad to other layers use multiple vias.
a.
b.
JA
to 102.9°C/W. Increasing the copper
ADP3338
c.
JA
even further
JA
is