AAT3221IGV-2.7-T1 查看數據表（PDF） - Advanced Analogic Technologies

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AAT3221IGV-2.7-T1

150mA NanoPower™ LDO Linear Regulator

Advanced Analogic Technologies 

PowerLinearTM

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AAT3221/2

150mA NanoPower™ LDO Linear Regulator

maximum conditions are calculated at the maximum

operating temperature where TA = 85°C, under normal

ambient conditions TA = 25°C. Given TA = 85°C, the

maximum package power dissipation is 267mW. At TA =

25°C, the maximum package power dissipation is

667mW.

The maximum continuous output current for the

AAT3221/2 is a function of the package power dissipa-

tion 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 = 2.5V and TA = 25°C,

IOUT(MAX) < 267mA. The output short-circuit protection

threshold is set between 150mA and 300mA. If the out-

put load current were to exceed 267mA or if the ambient

temperature were to increase, the internal die tempera-

ture 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 regula-

tor since the thermal protection circuit would only acti-

vate after a short-circuit event occured on the LDO

regulator output.

To determine the maximum input voltage for a given

load current, refer to the following equation. This calcu-

lation accounts for the total power dissipation of the LDO

regulator, including that caused by ground current.

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

This formula can be solved for VIN to determine the

maximum input voltage.

VIN(MAX)

=

(PD(MAX) + [VOUT · IOUT])

(IOUT + IGND)

The following is an example for an AAT3221/2 set for a

2.5 volt output:

VOUT = 2.5 volts

IOUT = 150mA

IGND = 1.1μA

(667mW + [2.5V · 150mA])

VIN(MAX) =

(150mA + 1.1µA)

VIN(MAX) = 6.95V

From the discussion above, PD(MAX) was determined to

equal 667mW at TA = 25°C. Thus, the AAT3221/2 can

sustain a constant 2.5V output at a 150mA load current

as long as VIN is ≤6.95V at an ambient temperature of

25°C. 5.5V is the maximum input operating voltage for

the AAT3221/2, thus at 25°C the device would not have

any thermal concerns or operational VIN(MAX) limits.

This situation can be different at 85°C. The following is

an example for an AAT3221/2 set for a 2.5 volt output

at 85°C:

VOUT = 2.5 volts

IOUT = 150mA

IGND = 1.1μA

(267mW + [2.5V · 150mA])

VIN(MAX) =

(150mA + 1.1µA)

VIN(MAX) = 4.28V

From the discussion above, PD(MAX) was determined to

equal 267mW at TA = 85°C.

Higher input-to-output voltage differentials can be

obtained with the AAT3221/2, while maintaining device

functions in the thermal safe operating area. To accom-

plish this, the device thermal resistance must be reduced

by increasing the heat sink area or by operating the LDO

regulator in a duty-cycled mode.

For example, an application requires VIN = 5.0V while

VOUT = 2.5V at a 150mA load and TA = 85°C. VIN is

greater than 4.28V, which is the maximum safe continu-

ous input level for VOUT = 2.5V at 150mA for TA = 85°C.

To maintain this high input voltage and output current

level, the LDO regulator must be operated in a duty-

cycled mode. Refer to the following calculation for duty-

cycle operation:

IGND = 1.1μA

IOUT = 150mA

VIN = 5.0 volts

VOUT = 2.5 volts

%DC

=

100

([VIN

-

PD(MAX)

VOUT]IOUT +

[VIN

·

IGND])

%DC

=

100

([5.0V

-

267mW

2.5V]150mA +

[5.0V

·

1.1µA])

%DC = 71.2%

PD(MAX) is assumed to be 267mW.

3221.2007.11.1.12

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