ADP3339 데이터 시트보기 (PDF) - Analog Devices

부품명

상세내역

제조사

ADP3339

High Accuracy, Ultralow IQ, 1.5 A, anyCAP® Low Dropout Regulator

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.

CALCULATING POWER DISSIPATION

Device power dissipation is calculated as follows:

PD = (VIN – VOUT) × ILOAD + (VIN × IGND)

Where ILOAD and IGND are load current and ground current, and

VIN and VOUT are the input and output voltages, respectively.

Assuming worst-case operating conditions are ILOAD = 1.5 A,

IGND = 14 mA, VIN = 3.3 V, and VOUT = 2.5 V, the device power

dissipation is

PD = (3.3 V – 2.5 V) × 1500 mA + (3.3 V × 14 mA) = 1246 mW

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

125°C − 85°C

θJA = 1.246 W = 32.1°C/W

PRINTED CIRCUIT BOARD LAYOUT

CONSIDERATIONS

The SOT-223’s thermal resistance, θJA, is determined by the sum

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

resistances. The junction-to-case thermal resistance, θJC, is

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), θJA is

126.6°C/W. Adding a small copper pad under the ADP3339

(Figure 22b) reduces the θJA to 102.9°C/W. Increasing the

copper pad to 1 square inch (Figure 22c) reduces the θJA even

further, to 52.8°C/W.

a

b

c

Figure 22. PCB Layouts

Rev. A | Page 10 of 12

Share Link: