AAT3220 Datasheet, PDF(11/16 Page) Advanced Analogic Technologies

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AAT3220 Datasheet, PDF (11/16 Pages) Advanced Analogic Technologies – 150mA NanoPower™ LDO Linear Regulator

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AAT3220

150mA NanoPowerâ¢ LDO Linear Regulator

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

IOUT(MAX) < 250mA. The output short circuit protec-

tion threshold is set between 150mA and 300mA.

If the output load current were to exceed 250mA or

if the ambient temperature were to increase, the

internal die temperature will increase. If the condi-

tion remained constant and the short circuit protec-

tion were not to activate, there would be a potential

damage hazard to LDO regulator since the thermal

protection circuit will only activate after a short cir-

cuit event occurs on the LDO regulator output.

To figure what the maximum input voltage would be

for a given load current refer to the following equa-

tion. This calculation accounts for the total power

dissipation of the LDO Regulator, including that

cause 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 x IOUT)) / (IOUT + IGND)

The following is an example for an AAT3220 set for

a 3.0 volt output:

From the discussion above, PD(MAX) was deter-

mined to equal 417mW at TA = 25Â°C.

VOUT = 3.0 volts

IOUT = 150mA

IGND = 1.1ÂµA

VIN(MAX)=(500mW+(3.0Vx150mA))/(150mA+1.1ÂµA)

VIN(MAX) > 5.5V

Thus, the AAT3220 can sustain a constant 3.0V

output at a 150mA load current as long as VIN is â¤

5.5V at an ambient temperature of 25Â°C. 5.5V is

the maximum input operating voltage for the

AAT3220, thus at 25Â°C, the device would not have

any thermal concerns or operational VIN(MAX) limits.

This situation can be different at 85Â°C. The follow-

ing is an example for an AAT3220 set for a 3.0 volt

output at 85Â°C:

From the discussion above, PD(MAX) was deter-

mined to equal 200mW at TA = 85Â°C.

VOUT = 3.0 volts

IOUT = 150mA

IGND = 1.1ÂµA

VIN(MAX)=(200mW+(3.0Vx150mA))/(150mA+1.1ÂµA)

VIN(MAX) = 4.33V

Higher input to output voltage differentials can be

obtained with the AAT3220, while maintaining

device functions in the thermal safe operating area.

To accomplish 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 = 3.0V at a 150mA load and TA = 85Â°C.

VIN is greater than 4.33V, which is the maximum

safe continuous input level for VOUT = 3.0V at

150mA for TA = 85Â°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:

PD(MAX) is assumed to be 200mW

IGND = 1.1ÂµA

IOUT = 150mA

VIN = 5.0 volts

VOUT = 3.0 volts

%DC = 100(PD(MAX / ((VIN - VOUT)IOUT + (VIN x IGND))

%DC=100(200mW/((5.0V-3.0V)150mA+(5.0Vx1.1ÂµA))

%DC = 66.67%

For a 150mA output current and a 2.0 volt drop

across the AAT3220 at an ambient temperature of

85Â°C, the maximum on time duty cycle for the

device would be 66.67%.

The following family of curves shows the safe oper-

ating area for duty cycled operation from ambient

room temperature to the maximum operating level.

3220.2001.09.1.0

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