AAT3200
OmniPower™ LDO Linear Regulator
At any given ambient temperature (TA), the maxi-
mum package power dissipation can be deter-
mined by the following equation:
This formula can be solved for VIN to determine the
maximum input voltage.
PD(MAX) + (VOUT × IOUT
)
VIN(MAX)
=
TJ(MAX) - TA
θJA
IOUT + IGND
PD(MAX)
=
Constants for the AAT3200 are TJ(MAX), the maxi-
mum junction temperature for the device which is
125°C and ΘJA = 200°C/W, the SOT23 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 following is an example for an AAT3200 set for
a 3.0 volt output:
From the discussion above, PD(MAX) was deter-
mined to equal 417mW at TA = 25°C.
VOUT
IOUT
IGND
= 3.0V
= 150mA
The maximum continuous output current for the
AAT3200 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:
= 20µA
500mW + (3.0V × 150mA)
VIN(MAX)
=
150mA + 20µA
VIN(MAX) > 5.5V
PD(MAX)
VIN - VOUT
Thus, the AAT3200 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
AAT3200, thus at 25°C, the device would not have
any thermal concerns or operational VIN(MAX) limits.
IOUT(MAX)
<
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
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.
This situation can be different at 85°C. The follow-
ing is an example for an AAT3200 set for a 3.0 volt
output at 85°C:
From the discussion above, PD(MAX) was deter-
mined to equal 200mW at TA = 85°C.
VOUT
IOUT
IGND
= 3.0V
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.
= 150mA
= 20µA
200mW + (3.0V × 150mA)
VIN(MAX)
=
150mA + 20µA
VIN(MAX) = 4.33V
PD(MAX) = (VIN - VOUT)IOUT + (VIN × IGND
)
3200.2005.04.1.1
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