ADP3331ART(RevA) View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

ADP3331ART
(Rev.:RevA)

Adjustable Output Ultralow IQ, 200 mA, SOT-23, anyCAP® Low Dropout Regulator

Analog Devices 

ADP3331

SILICON

DIE

SILICON DIE

WITH

ELECTRICALLY

ISOLATED

DIE ATTACH

NORMAL SOT-23-6 PACKAGE

THERMALLY ENHANCED

CHIP-ON-LEAD PACKAGE

Figure 4. Chip-on-Lead Package

Calculating Junction Temperature

Device power dissipation is calculated as follows:

( ) ( ) PD = VIN - VOUT ILOAD + VIN IGND

(8)

Where ILOAD and IGND are load current and ground current and

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

Assuming that the worst case operating conditions are ILOAD =

200 mA, IGND = 4 mA, VIN = 4.2 V, and VOUT = 3.0 V, the

device power dissipation is

PD = (4.2 V - 3.0 V ) 200 mA + (4.2 V ) 4 mA = 257 mW (9)

The proprietary package used on the ADP3331 has a thermal

resistance of 165∞C/W when placed on a 4-layer board and

190∞C/W when placed on a 2-layer board. This allows the ambient

temperature to be significantly higher for a given power dissipa-

tion than with a standard package. Assuming a 4-layer board, the

junction temperature rise above ambient will be approximately

equal to

D TJA = 0.257 W ¥ 165oC/W = 42.4oC

(10)

To limit the junction temperature to 125∞C, the maximum

allowable ambient temperature is

TA( MAX ) = + 125oC - 42.4oC = 82.6oC

(11)

Shutdown Mode

Applying a TTL level high signal to the shutdown (SD) pin, or

tying it to the input pin, will turn the output ON. Pulling the

SD to 0.4 V or below, or tying it to ground, will turn the output

OFF. In shutdown mode, the quiescent current is reduced to

less than 1 mA.

Error Flag Dropout Detector

The ADP3331 will maintain its output voltage over a wide

range of load, input voltage, and temperature conditions. If the

output is about to lose regulation due to the input voltage

approaching the dropout level, the error flag will be activated.

The ERR output is an open collector, which will be driven low.

Once set, the ERR flag’s hysteresis will keep the output low until

a small margin of operating range is restored either by raising

the supply voltage or reducing the load.

Low Voltage Applications

In applications where the output voltage is 2.2 V or less, the

ADP3331 may begin to exhibit some turn-on overshoot. The

degree of overshoot is determined by several factors: the output

voltage setting, the output load, the noise reduction capacitor,

and the output capacitor.

The output voltage setting is determined by the application and

cannot be tailored for minimum overshoot. In general, for output

voltages of 2.2 V or less, the overshoot becomes larger as the

output voltage decreases.

The output load is also determined by the system requirements.

However, if the ADP3331 has no load on the output during

startup, a small amount of preload can be added to minimize

overshoot. A preload of 2 mA to 20 mA is recommended.

A noise reduction capacitor, if not already being used, is sug-

gested to reduce the overshoot. Values in the range of 10 pF to

100 pF work best, along with the preload suggested previously.

The output capacitor can be adjusted to minimize the over-

shoot. Values in the 0.47 mF to 1.0 mF range should be used in

conjunction with the preload and noise reduction capacitor.

Further increases in the output capacitance may be acceptable if

the output already has a sizable load during startup.

Higher Output Current

The ADP3331 can source up to 200 mA without any heat sink

or pass transistor. If higher current is needed, an appropriate pass

transistor can be used, as in Figure 5, to increase the output

current to 1 A.

VIN = 3.3V

C1

47␮F

MJE253*

R1

50⍀

VOUT = 1.8V @ 1A

IN OUT

ADP3331

SD

FB

GND ERR

*REQUIRES HEAT SINK

C2

10␮F 340k⍀

698k⍀

Figure 5. High Output Current Linear Regulator

Printed Circuit Board Layout Considerations

Use the following general guidelines when designing printed

circuit boards:

1. PC board traces with larger cross sectional areas will remove

more heat from the ADP3331. For optimum heat transfer,

specify thick copper and use wide traces.

2. The thermal resistance can be decreased by approximately

10% by adding a few square centimeters of copper area to

the lands connected to the pins of the LDO.

3. The feedback pin is a high impedance input, and care should

be taken when making a connection to this pin. The voltage

setting resistors and noise reduction network must be located

as close as possible. Long PC board traces are not recom-

mended. Avoid routing traces near possible noise sources.

–8–

REV. A

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