ADP3339AKC15RL7 Analog Devices, ADP3339AKC15RL7 Datasheet - Page 10

• Manufacturer Part Number: ADP3339AKC15RL7
• Description: High-Accuracy Ultralow Iq, 1.5 A, anyCAP Low Dropout Regulator
• Manufacturer: Analog Devices

ADP3339
APPLICATION INFORMATION
CAPACITOR SELECTION
Output Capacitor
The stability and transient response of the LDO is a function of
the output capacitor. The ADP3339 is stable with a wide range
of capacitor values, types, and ESR (anyCAP). A capacitor as low
as 1 µF is all that is needed for stability. A higher capacitance
may be necessary if high output current surges are anticipated,
or if the output capacitor cannot be located near the output and
ground pins. The ADP3339 is stable with extremely low ESR
capacitors (ESR ≈ 0) such as multilayer ceramic capacitors
(MLCC) or OSCON. Note that the effective capacitance of some
capacitor types falls below the minimum over temperature or
with dc voltage.
Input Capacitor
An input bypass capacitor is not strictly required but is recom-
mended in any application involving long input wires or high
source impedance. Connecting a 1 µF capacitor from the input
to ground reduces the circuit’s sensitivity to PC board layout
and input transients. If a larger output capacitor is necessary, a
larger value input capacitor is also recommended.
OUTPUT CURRENT LIMIT
The ADP3339 is short-circuit protected by limiting the pass
transistor’s base drive current. The maximum output current is
limited to about 3 A. See Figure 16.
THERMAL OVERLOAD PROTECTION
The ADP3339 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 tempera-
ture and power dissipation) where the die temperature starts to
rise above 160°C, the output current is reduced until the die
temperature 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 the junction temperature does not exceed 150°C.
Rev. A | Page 10 of 12
CALCULATING POWER DISSIPATION
Device power dissipation is calculated as follows:
Where I
V
Assuming worst-case operating conditions are I
I
dissipation is
So, for a junction temperature of 125°C and a maximum
ambient 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
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 Figure 22, the amount of copper to which the
ADP3339 is mounted affects thermal performance. When
mounted to the minimal pads of 2 oz. copper (Figure 22a), θ
126.6°C/W. Adding a small copper pad under the ADP3339
(Figure 22b) reduces the θ
copper pad to 1 square inch (Figure 22c) reduces the θ
further, to 52.8°C/W.
GND
P
IN
D
and V
= (3.3 V – 2.5 V) × 1500 mA + (3.3 V × 14 mA) = 1246 mW
= 14 mA, V
a
LOAD
OUT
and I
P
are the input and output voltages, respectively.
D
θ
= (V
IN
JA
GND
= 3.3 V, and V
=
IN
b
are load current and ground current, and
125
– V
Figure 22. PCB Layouts
. 1
°
OUT
246
JA
C
to 102.9°C/W. Increasing the
−
) × I
85
W
OUT
°
LOAD
C
= 2.5 V, the device power
JA
=
, is determined by the sum
+ (V
32
1 .
IN
°
C/W
c
× I
GND
LOAD
)
= 1.5 A,
JC
JA
, is
even
JA
is