AAT3223
250mA NanoPower™ LDO
Linear Regulator with Power-OK
remain in a shutdown state until the internal die
temperature falls back below the 140°C trip point.
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 267mW. At TA = 25°C, the
maximum package power dissipation is 667mW.
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.
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:
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.
PD(MAX)
VIN - VOUT
IOUT(MAX)
<
For example, if VIN = 5V, VOUT = 2.8V and TA =
25°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.
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.
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.
At any given ambient temperature (TA), the maxi-
mum package power dissipation can be deter-
mined by the following equation:
PD(MAX) = (VIN - VOUT)IOUT + (VIN x IGND
)
This formula can be solved for VIN to determine the
maximum input voltage.
TJ(MAX) - TA
θJA
PD(MAX)
=
PD(MAX) + (VOUT × IOUT
)
VIN(MAX)
=
IOUT + IGND
Constants for the AAT3223 are TJ(MAX), the maxi-
mum junction temperature for the device which is
125°C, and ΘJA = 150°C/W, the package thermal
12
3223.2006.03.1.5
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
