AAT3216 ETC, AAT3216 Datasheet - Page 11

• Manufacturer Part Number: AAT3216
• Description: 150mA MicroPower LDO with PowerOK
• Manufacturer: ETC

Applications Information
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 following discussions will assume the LDO reg-
ulator is mounted on a printed circuit board utilizing
the minimum recommended footprint as stated in
the layout considerations section of the document.
At any given ambient temperature (T
mum package power dissipation can be deter-
mined by the following equation:
Constants for the AAT3216 are T
mum junction temperature for the device which is
125°C and
resistance. Typically, maximum conditions are cal-
culated at the maximum operating temperature
where T
T
power dissipation is 211mW. At T
maximum package power dissipation is 526mW.
The maximum continuous output current for the
AAT3216 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:
For example, if V
I
exceed 264mA or if the ambient temperature were to
increase, the internal die temperature will increase.
If the condition remained constant, the LDO regula-
tor thermal protection circuit will activate.
To figure what the maximum input voltage would be
for a given load current refer to the following equa-
tion. This calculation accounts for the total power
dissipation of the LDO Regulator, including that
caused by ground current.
3216.2004.01.0.94
OUT(MAX)
A
= 25°C. Given T
P
D(MAX)
A
< 264mA. If the output load current were to
I
OUT(MAX)
= 85°C, under normal ambient conditions
P
D(MAX)
JA
= (V
= 190°C/W, the package thermal
IN
IN
< P
= [T
= 5V, V
A
- V
= 85°, the maximum package
D(MAX)
OUT
J(MAX)
)I
OUT
OUT
/ (V
- T
= 3V and T
+ (V
A
IN
] /
J(MAX)
- V
A
IN
JA
OUT
= 25°C°, the
x I
A
) the maxi-
, the maxi-
GND
)
A
)
= 25°,
150mA MicroPower™ LDO with PowerOK
This formula can be solved for V
maximum input voltage.
The following is an example for an AAT3216 set for
a 2.5 volt output:
From the discussion above, P
mined to equal 526mW at T
V
I
I
V
V
Thus, the AAT3216 can sustain a constant 2.5V
output at a 150mA load current as long as V
6.00V at an ambient temperature of 25°C. 6.0V is
the absolute maximum voltage where an AAT3216
would never be operated, thus at 25°C, the device
would not have any thermal concerns or opera-
tional V
This situation can be different at 85°C. The follow-
ing is an example for an AAT3216 set for a 2.5 volt
output at 85°C:
From the discussion above, P
mined to equal 211mW at T
V
I
I
V
V
Higher input to output voltage differentials can be
obtained with the AAT3216, while maintaining
device functions within the thermal safe operating
area.
resistance must be reduced by increasing the heat
sink area or by operating the LDO regulator in a
duty cycled mode.
For example, an application requires V
while V
V
safe continuous input level for V
150mA for T
voltage and output current level, the LDO regulator
OUT
GND
OUT
GND
V
OUT
IN(MAX)
IN(MAX)
OUT
IN(MAX)
IN(MAX)
IN
IN(MAX)
is greater than 3.90V, which is the maximum
= 150mA
= 150mA
= 150µA
= 150uA
= 2.5 volts
= 2.5 volts
OUT
=(526mW+(2.5Vx150mA))/(150mA +150µA)
=(211mW+(2.5Vx150mA))/(150mA +150uA)
IN(MAX)
To accomplish this, the device thermal
= 6.00V
= 3.90V
= (P
= 2.5V at a 150mA load and T
A
D(MAX)
limits.
= 85°C. To maintain this high input
+ (V
OUT
A
A
x I
= 85°C.
= 25°C.
OUT
IN
D(MAX)
D(MAX)
AAT3216
)) / (I
to determine the
OUT
OUT
was deter-
was deter-
= 2.5V at
IN
A
+ I
= 85°C.
= 4.2V
IN
GND
is
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