AAT3242
300mA/150mA Dual CMOS LDO Linear Regulator
Thermal Considerations and High
Output Current Applications
TJ(MAX) - TA
θJA
PD(MAX)
=
The AAT3242 is designed to deliver continuous
output load currents of 300mA and 150mA under
normal operations, and can supply up to 500mA
during circuit start-up conditions. This is desirable
for circuit applications where there might be a brief
high in-rush current during a power-on event.
Constants for the AAT3242 are TJ(MAX) (the maxi-
mum junction temperature for the device, which is
125°C) and θJA = 110°C/W (the package thermal
resistance). Typically, maximum conditions are cal-
culated at the maximum operating temperature of TA
= 85°C and under normal ambient conditions where
TA = 25°C. Given TA = 85°C, the maximum package
power dissipation is 364mW. At TA = 25°C, the max-
imum package power dissipation is 909mW.
The limiting characteristic for the maximum output
load current 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 need to be taken into account.
The maximum continuous output current for the
AAT3242 is a function of the package power dissi-
pation and the input-to-output voltage drop across
the LDO regulator. To determine the maximum
output current for a given output voltage, refer to
the following equation. This calculation accounts
for the total power dissipation of the LDO regulator,
including that caused by ground current.
The following discussions will assume the LDO
regulator is mounted on a printed circuit board uti-
lizing the minimum recommended footprint as stat-
ed in the layout considerations section of this doc-
ument. At any given ambient temperature (TA), the
maximum package power dissipation can be deter-
mined by the following equation:
PD(MAX) = [(VIN - VOUTA)IOUTA + (VIN x IGND)] + [(VIN - VOUTB)IOUTB + (VIN x IGND)]
This formula can be solved for IOUTA to determine the maximum output current for LDOA:
P
D(MAX) - (2×VIN × IGND) - (VIN - VOUTB) × IOUTB
VIN - VOUTA
IOUTA(MAX)
=
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3242.2006.04.1.10
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
