參數(shù)資料
型號： AAT3221
廠商： Advanced Analogic Technologies, Inc.
英文描述： 150mA NanoPower⑩ LDO Linear Regulator
中文描述： 150mA的NanoPower⑩LDO線性穩(wěn)壓器
文件頁數(shù)： 11/16頁
文件大?。?/td> 390K
代理商： AAT3221
AAT3221/2
150mA NanoPower LDO Linear Regulator
3221.200
2
.
03
.0.9
4
11
T
A
= 25°C. Given T
A
= 85°, the maximum package
power dissipation is 267mW. At T
A
= 25°C°, the
maximum package power dissipation is 667mW.
The maximum continuous output current for the
AAT3221/2 is a function of the package power dis-
sipation and the input to output voltage drop across
the LDO regulator. Refer to the following simple
equation:
I
OUT(MAX)
< P
D(MAX)
/ (V
IN
- V
OUT
)
For example, if V
IN
= 5V, V
OUT
= 2.5V and T
A
= 25°,
I
OUT(MAX)
< 267mA. The output short circuit protec-
tion 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 inter-
nal die temperature will increase. If the condition
remained constant and the short circuit protection
did not activate, there would be a potential damage
hazard to LDO regulator since the thermal protection
circuit will only activate after a short circuit event
occurs on the LDO regulator output.
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.
P
D(MAX)
= (V
IN
- V
OUT
)I
OUT
+ (V
IN
x I
GND
)
This formula can be solved for VIN to determine
the maximum input voltage.
V
IN(MAX)
= (P
D(MAX)
+ (V
OUT
x I
OUT
)) / (I
OUT
+ I
GND
)
The following is an example for an AAT3221/2 set
for a 2.5 volt output:
From the discussion above, P
D(MAX)
was deter-
mined to equal 667mW at T
A
= 25°C.
V
OUT
= 2.5 volts
I
OUT
= 150mA
I
GND
= 1.1μA
V
IN(MAX)
=(667mW+(2.5Vx150mA))/(150mA +1.1μA)
V
IN(MAX)
= 6.95V
Thus, the AAT3221/2 can sustain a constant 2.5V
output at a 150mA load current as long as V
IN
is
≤
6.95V at an ambient temperature of 25°C. 5.5V is
the maximum input operating voltage for the
AAT3221/2, thus at 25°C, the device would not have
any thermal concerns or operational V
IN(MAX)
limits.
This situation can be different at 85°C. The follow-
ing is an example for an AAT3221/2 set for a 2.5
volt output at 85°C:
From the discussion above, P
D(MAX)
was deter-
mined to equal 267mW at T
A
= 85°C.
V
OUT
= 2.5 volts
I
OUT
= 150mA
I
GND
= 1.1μA
V
IN(MAX)
=(267mW+(2.5Vx150mA))/(150mA +1.1μA)
V
IN(MAX)
= 4.28V
Higher input to output voltage differentials can be
obtained with the AAT3221/2, while maintaining
device functions in the thermal safe operating area.
To accomplish this, the device thermal 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
IN
= 5.0V
while V
OUT
= 2.5V at a 150mA load and T
A
= 85°C.
V
IN
is greater than 4.28V, which is the maximum
safe continuous input level for V
OUT
= 2.5V at
150mA for T
A
= 85°C. To maintain this high input
voltage and output current level, the LDO regulator
must be operated in a duty cycled mode. Refer to
the following calculation for duty cycle operation:
P
D(MAX)
is assumed to be 267mW
I
GND
= 1.1μA
I
OUT
= 150mA
V
IN
= 5.0 volts
V
OUT
= 2.5 volts
%DC = 100(P
D(MAX)
/ ((V
IN
- V
OUT
)I
OUT
+ (V
IN
x I
GND
))
%DC=100(267mW/((5.0V-2.5V)150mA+(5.0Vx1.1μA))
%DC = 71.2%
For a 150mA output current and a 2.5 volt drop
across the AAT3221/2 at an ambient temperature
of 85°C, the maximum on time duty cycle for the
device would be 71.2%.
The following family of curves shows the safe oper-
ating area for duty cycled operation from ambient
room temperature to the maximum operating level.
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