AAT3218IGV-2.6-T1 데이터 시트보기 (PDF) - Advanced Analogic Technologies

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AAT3218IGV-2.6-T1

150mA MicroPower™ High Performance LDO

Advanced Analogic Technologies 

AAT3218

150mA MicroPower™ High Performance LDO

No-Load Stability

The AAT3218 is designed to maintain output volt-

age regulation and stability under operational no-

load conditions. This is an important characteristic

for applications where the output current may drop

to zero.

Reverse Output-to-Input Voltage

Conditions and Protection

Under normal operating conditions, a parasitic

diode exists between the output and input of the

LDO regulator. The input voltage should always

remain greater than the output load voltage, main-

taining a reverse bias on the internal parasitic

diode. Conditions where VOUT might exceed VIN

should be avoided since this would forward bias

the internal parasitic diode and allow excessive

current flow into the VOUT pin, possibly damaging

the LDO regulator.

In applications where there is a possibility of VOUT

exceeding VIN for brief amounts of time during nor-

mal operation, the use of a larger value CIN capaci-

tor is highly recommended. A larger value of CIN

with respect to COUT will effect a slower CIN decay

rate during shutdown, thus preventing VOUT from

exceeding VIN. In applications where there is a

greater danger of VOUT exceeding VIN for extended

periods of time, it is recommended to place a

Schottky diode across VIN to VOUT (connecting the

cathode to VIN and anode to VOUT). The Schottky

diode forward voltage should be less than 0.45V.

Thermal Considerations and High

Output Current Applications

The AAT3218 is designed to deliver a continuous

output load current of 150mA under normal operat-

ing conditions. The limiting characteristic for the

maximum output load current safe operating area

is essentially package power dissipation and the

internal preset thermal limit of the device. In order

to obtain high operating currents, careful device

layout and circuit operating conditions must be

taken into account.

The following discussions will assume the LDO reg-

ulator is mounted on a printed circuit board utilizing

the minimum recommended footprint, as stated in

the Layout Considerations section of this datasheet.

At any given ambient temperature (TA), the maxi-

mum package power dissipation can be deter-

mined by the following equation:

PD(MAX) =

[TJ(MAX) - TA]

θJA

Constants for the AAT3218 are TJ(MAX), the maxi-

mum junction temperature for the device which is

125°C and ΘJA = 190°C/W, the package thermal

resistance. Typically, maximum conditions are cal-

culated at the maximum operating temperature

where TA = 85°C, under normal ambient conditions

TA = 25°C. Given TA = 85°C, the maximum pack-

age power dissipation is 211mW. At TA = 25°C, the

maximum package power dissipation is 526mW.

The maximum continuous output current for the

AAT3218 is a function of the package power dissi-

pation and the input-to-output voltage drop across

the LDO regulator. Refer to the following simple

equation:

IOUT(MAX) <

PD(MAX)

(VIN - VOUT)

For example, if VIN = 5V, VOUT = 3V, and TA = 25°C,

IOUT(MAX) < 264mA. If the output load current were

to exceed 264mA or if the ambient temperature

were to increase, the internal die temperature

would increase. If the condition remained con-

stant, the LDO regulator thermal protection circuit

would activate.

To determine the maximum input voltage for a

given load current, refer to the following equation.

This calculation accounts for the total power dissi-

pation of the LDO regulator, including that caused

by ground current.

PD(MAX) = (VIN - VOUT)IOUT + (VIN x IGND)

3218.2006.04.1.8

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