AAT3220IGY-3.3-T1 Просмотр технического описания (PDF) - Advanced Analog Technology, Inc.

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AAT3220IGY-3.3-T1

150mA NanoPower™ LDO Linear Regulator

Advanced Analog Technology, Inc. 

AAT3220

150mA NanoPower™ LDO Linear Regulator

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

mum package power dissipation can be deter-

mined by the following equation:

PD(MAX)

=

TJ(MAX) -

θJA

TA

Constants for the AAT3220 are TJ(MAX), the maxi-

mum junction temperature for the device which is

125°C and ΘJA = 200°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 200mW. At TA = 25°C, the

maximum package power dissipation is 500mW.

The maximum continuous output current for the

AAT3220 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) < 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 inter-

nal 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 pro-

tection 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 × 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 AAT3220 set for

a 3.0V output:

VOUT = 3.0V

IOUT = 150mA

IGND = 1.1µA

500mW + (3.0V × 150mA)

VIN(MAX) =

150mA + 1.1µA

VIN(MAX) = > 5.5V

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

mined to equal 417mW at TA = 25°C.

Thus, the AAT3220 can sustain a constant 3.0V

output at a 150mA load current as long as VIN is ≤

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

the maximum input operating voltage for the

AAT3220, 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 follow-

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

output at 85°C:

VOUT = 3.0V

IOUT = 150mA

IGND = 1.1µA

200mW + (3.0V × 150mA)

VIN(MAX) =

150mA + 1.1µA

VIN(MAX) = 4.33V

3220.2006.01.1.4

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