AAT3220
150mA NanoPower™ LDO Linear Regulator
From the discussion above, P
D(MAX)
was deter-
mined to equal 200mW at T
A
= 85°C.
Higher input-to-output voltage differentials can be
obtained with the AAT3220 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
= 3.0V at a 150mA load and T
A
= 85°C.
V
IN
is greater than 4.33V, which is the maximum
safe continuous input level for V
OUT
= 3.0V 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:
3.5
3.5
Device Duty Cycle vs. V
DROP
(V
OUT
= 2.5V @ 25°C)
Voltage Drop (V)
3
2.5
2
1.5
1
0.5
0
0
10
20
30
40
50
60
70
80
90
100
200mA
150mA
Duty Cycle (%)
Device Duty Cycle vs. V
DROP
(V
OUT
= 2.5V @ 50°C)
3
2.5
2
1.5
1
0.5
0
0
10
20
30
40
50
60
70
80
90
100
Voltage Drop (V)
I
GND
I
OUT
V
IN
= 1.1µA
= 150mA
= 5.0V
200mA
150mA
V
OUT
= 3.0V
P
D(MAX)
%DC = 100
(V
IN
- V
OUT
)I
OUT
+ (V
IN
×
I
GND
)
%DC = 100
200mW
(5.0V - 3.0V)150mA + (5.0V
×
1.1µA)
Duty Cycle (%)
%DC = 66.67%
P
D(MAX)
is assumed to be 200mW
Voltage Drop (V)
3.5
3
2.5
2
1.5
1
0.5
0
0
10
Device Duty Cycle vs. V
DROP
(V
OUT
= 2.5V @ 85°C)
100mA
For a 150mA output current and a 2.0V drop across
the AAT3220 at an ambient temperature of 85°C,
the maximum on-time duty cycle for the device
would be 66.67%.
The following family of curves shows the safe oper-
ating area for duty-cycled operation from ambient
room temperature to the maximum operating level.
200mA
150mA
20
30
40
50
60
70
80
90
100
Duty Cycle (%)
12
3220.2006.01.1.4
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
