AAT3223_06 Datasheet, PDF(12/17 Page) Advanced Analogic Technologies – 250mA NanoPower™ LDO Linear Regulator with Power-OK

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AAT3223_06 Datasheet, PDF (12/17 Pages) Advanced Analogic Technologies – 250mA NanoPower™ LDO Linear Regulator with Power-OK

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remain in a shutdown state until the internal die

temperature falls back below the 140Â°C trip point.

The interaction between the short-circuit and ther-

mal protection systems allows the LDO regulator to

withstand indefinite short-circuit conditions without

sustaining permanent damage.

No-Load Stability

The AAT3223 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. An output capacitor is required for stability

under no-load operating conditions. Refer to the

Output Capacitor section of this datasheet for rec-

ommended typical output capacitor values.

Thermal Considerations and High

Output Current Applications

The AAT3223 is designed to deliver a continuous

output load current up to 250mA under normal

operating conditions. The limiting characteristic for

the maximum output load 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 regulator is mounted on a printed

circuit board utilizing the minimum recommended

footprint and the printed circuit board is 0.062-inch

thick FR4 material with one ounce copper.

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

mum package power dissipation can be deter-

mined by the following equation:

PD(MAX)

TJ(MAX) -

Î¸JA

Constants for the AAT3223 are TJ(MAX), the maxi-

mum junction temperature for the device which is

125Â°C, and ÎJA = 150Â°C/W, the package thermal

AAT3223

250mA NanoPowerâ¢ LDO

Linear Regulator with Power-OK

resistance. Typically, maximum conditions are cal-

culated at the maximum operating temperature

where TA = 85Â°C, under normal ambient conditions

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

age power dissipation is 267mW. At TA = 25Â°C, the

maximum package power dissipation is 667mW.

The maximum continuous output current for the

AAT3223 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 = 2.8V and TA =

25Â°C, IOUT(MAX) < 267mA. The output short-circuit

protection threshold is set between 300mA and

450mA. If the output load current were to exceed

267mA or if the ambient temperature were to

increase, the internal die temperature would

increase. If the condition remained constant and

the short-circuit protection did not activate, there

would be a potential damage hazard to the LDO

regulator since the thermal protection circuit will

only activate after a short-circuit event occurs on

the LDO regulator output.

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)

This formula can be solved for VIN to determine the

maximum input voltage.

VIN(MAX) =

PD(MAX) + (VOUT Ã IOUT)

IOUT + IGND

3223.2006.03.1.5

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