AAT3220
150mA NanoPower™ LDO Linear Regulator
From the discussion above, PD(MAX) was deter-
mined to equal 200mW at TA = 85°C.
Device Duty Cycle vs. VDROP
(VOUT = 2.5V @ 25°C)
3.5
3
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.
2.5
2
200mA
150mA
1.5
1
0.5
0
0
10
20
30
40
50
60
70
80
90
100
For example, an application requires VIN = 5.0V
while VOUT = 3.0V at a 150mA load and TA = 85°C.
VIN is greater than 4.33V, which is the maximum
safe continuous input level for VOUT = 3.0V at
150mA for TA = 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:
Duty Cycle (%)
Device Duty Cycle vs. VDROP
(VOUT = 2.5V @ 50°C)
3.5
3
IGND = 1.1µA
IOUT = 150mA
VIN = 5.0V
VOUT = 3.0V
2.5
2
200mA
150mA
1.5
1
0.5
0
0
10
20
30
40
50
60
70
80
90
100
PD(MAX)
(VIN - VOUT)IOUT + (VIN × IGND
Duty Cycle (%)
%DC = 100
)
200mW
(5.0V - 3.0V)150mA + (5.0V × 1.1µA)
%DC = 100
%DC = 66.67%
Device Duty Cycle vs. VDROP
(VOUT = 2.5V @ 85°C)
PD(MAX) is assumed to be 200mW
3.5
3
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%.
2.5
2
1.5
1
200mA
150mA
0.5
0
The following family of curves shows the safe oper-
ating area for duty-cycled operation from ambient
room temperature to the maximum operating level.
0
10
20
30
40
50
60
70
80
90
100
Duty Cycle (%)
12
3220.2006.01.1.4
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
