AAT3220 Datasheet, PDF(10/16 Page) Advanced Analogic Technologies

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AAT3220 Datasheet, PDF (10/16 Pages) Advanced Analogic Technologies – 150mA NanoPower™ LDO Linear Regulator

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AAT3220

150mA NanoPowerâ¢ LDO Linear Regulator

ceramic capacitors, typically greater than 2.2ÂµF are

often available in the low cost Y5V and Z5U dielec-

trics. These two material types are not recommend-

ed for use with LDO regulators since the capacitor

tolerance can vary by more than Â±50% over the

operating temperature range of the device. A 2.2ÂµF

Y5V capacitor could be reduced to 1ÂµF over the full

operating temperature range. This can cause prob-

lems for circuit operation and stability. X7R and X5R

dielectrics are much more desirable. The tempera-

ture tolerance of X7R dielectric is better than Â±15%.

Capacitor area is another contributor to ESR.

Capacitors, which are physically large in size will

have a lower ESR when compared to a smaller

sized capacitor of equivalent material and capaci-

tance value. These larger devices can also improve

circuit transient response when compared to an

equal value capacitor in a smaller package size.

Consult capacitor vendor data sheets carefully when

selecting capacitors for use with LDO regulators.

Short Circuit Protection and Thermal

Protection

The AAT3220 is protected by both current limit and

over temperature protection circuitry. The internal

short circuit current limit is designed to activate

when the output load demand exceeds the maxi-

mum rated output. If a short circuit condition were

to continually draw more than the current limit

threshold, the LDO regulator's output voltage will

drop to a level necessary to supply the current

demanded by the load. Under short circuit or other

over current operating conditions, the output volt-

age will drop and the AAT3220's die temperature

will increase rapidly. Once the regulator's power

dissipation capacity has been exceeded and the

internal die temperature reaches approximately

140Â°C the system thermal protection circuit will

become active. The internal thermal protection cir-

cuit will actively turn off the LDO regulator output

pass device to prevent the possibility of over tem-

perature damage. The LDO regulator output will

remain in a shutdown state until the internal die

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

The combination and interaction between the short

circuit and thermal protection systems allow the

LDO regulator to withstand indefinite short circuit

conditions without sustaining permanent damage.

No-Load Stability

The AAT3220 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 considerations section for recom-

mended typical output capacitor values.

Thermal Considerations and High

Output Current Applications

The AAT3220 is designed to deliver a continuous

output load current of 150mA under normal operat-

ing conditions. The limiting characteristic for the

maximum output load safe operating area is essen-

tially package power dissipation and the internal pre-

set thermal limit of the device. In order to obtain high

operating currents, careful device layout and circuit

operating conditions need to 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 and the print-

ed 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) - TA] / Î JA

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

mum junction temperature for the device which is

125Â°C and ÎJA = 200Â°C/W, the package thermal

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 200mW. At TA = 25Â°CÂ°, 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)

3220.2001.09.1.0

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