AAT3201
150mA OmniPower™ LDO Linear Regulator
At any given ambient temperature (T
A
), the maxi-
mum package power dissipation can be deter-
mined by the following equation:
T
J(MAX)
- T
A
θ
JA
This formula can be solved for V
IN
to determine the
maximum input voltage.
P
D(MAX)
+ (V
OUT
×
I
OUT
)
I
OUT
+ I
GND
P
D(MAX)
=
V
IN(MAX)
=
Constants for the AAT3201 are T
J(MAX)
, the maxi-
mum junction temperature for the device which is
125°C, and
Θ
JA
= 150°C/W, the package thermal
resistance. Typically, maximum conditions are cal-
culated at the maximum operating temperature
where T
A
= 85°C, under normal ambient conditions
T
A
= 25°C. Given T
A
= 85°C, the maximum pack-
age power dissipation is 267mW. At T
A
= 25°C, the
maximum package power dissipation is 667mW.
The maximum continuous output current for the
AAT3201 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:
P
D(MAX)
I
OUT(MAX)
<
V
IN
- V
OUT
For example, if V
IN
= 5V, V
OUT
= 2.5V, and T
A
=
25°C, I
OUT(MAX)
<267mA. The output short-circuit
protection threshold is set between 150mA and
300mA. If the output load current were to exceed
267mA or if the ambient temperature were to
increase, the internal die temperature will increase.
If the condition remained constant and the short-cir-
cuit 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 out-
put.
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.
P
D(MAX)
= (V
IN
- V
OUT
)I
OUT
+ (V
IN
×
I
GND
)
The following is an example for an AAT3201 set for
a 2.5 volt output:
V
OUT
I
OUT
I
GND
= 2.5V
= 150mA
= 20µA
667mW + (2.5V
×
150mA)
150mA + 20µA
V
IN(MAX)
=
V
IN(MAX)
= 6.95V
From the discussion above, P
D(MAX)
was deter-
mined to equal 667mW at T
A
= 25°C.
Thus, the AAT3201 can sustain a constant 2.5V out-
put at a 150mA load current as long as V
IN
is
≤
6.95V
at an ambient temperature of 25°C. 5.5V is the max-
imum input operating voltage for the AAT3201, thus
at 25°C the device would not have any thermal con-
cerns or operational V
IN(MAX)
limits.
This situation can be different at 85°C. The follow-
ing is an example for an AAT3201 set for a 2.5 volt
output at 85°C:
V
OUT
I
OUT
I
GND
= 2.5V
= 150mA
= 20µA
267mW + (2.5V
×
150mA)
150mA + 20µA
V
IN(MAX)
=
V
IN(MAX)
= 4.28V
From the discussion above, P
D(MAX)
was deter-
mined to equal 267mW at T
A
= 85°C.
3201.2006.01.1.2
11
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