ADP3338

Rev. B | Page 10 of 16

APPLICATION INFORMATION

CAPACITOR SELECTION

Output Capacitor

The stability and transient response of the LDO is a function of

the output capacitor. The ADP3338 is stable with a wide range

of capacitor values, types, and ESR (anyCAP). A capacitor as

low as 1 µF is the only requirement for stability. A higher ca-

pacitance 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 ADP3338 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 sensitivity of the circuit to PC board

layout and input transients. If a larger output capacitor is

necessary, a larger value input capacitor is recommended.

OUTPUT CURRENT LIMIT

The ADP3338 is short-circuit protected by limiting the pass

transistor’s base drive current. The maximum output current is

limited to approximately 2 A (see Figure 16).

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, such as high ambient

temperature 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, externally limit the power dissipation of the device

so the junction temperature does not exceed 150°C.

CALCULATING POWER DISSIPATION

Device power dissipation is calculated as

Where

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

C/W

48

W

833

.

0

C

85

C

125

°

=

°

−

°

=

PRINTED CIRCUIT BOARD LAYOUT

CONSIDERATIONS

sum of the junction-to-case and the case-to-ambient thermal

determined by the package design and is 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

ADP3338 is mounted affects thermal performance. When

mounted to the minimal pads of 2 oz. copper, as shown in

102.9°C/W. Increasing the copper pad to one square inch, as

c

ab

Figure 22. PCB Layouts