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參數(shù)資料
| 型號： | AAT3221IJS-3.3-T1 |
| 廠商： | Advanced Analog Technology,lnc. |
| 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)： | 12/18頁 |
| 文件大?。?/td> | 198K |
| 代理商： | AAT3221IJS-3.3-T1 |
AAT3221/2
150mA NanoPower LDO Linear Regulator
12
3221.2005.12.1.11
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
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°C,
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 would increase. If the condition
remained constant and the short-circuit protection
did not activate, there would be a potential damage
hazard to the LDO regulator since the thermal pro-
tection circuit would only activate after a short-circuit
event occured on the LDO regulator output.
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
x I
GND
)
This formula can be solved for V
IN
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:
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
From the discussion above, P
D(MAX)
was deter-
mined to equal 667mW at T
A
= 25°C. 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 con-
cerns 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:
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
From the discussion above, P
D(MAX)
was deter-
mined to equal 267mW at T
A
= 85°C.
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:
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%
P
D(MAX)
is assumed to be 267mW.
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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