AAT3236
300mA CMOS High Performance LDO
V
OUT
I
OUT
I
GND
V
IN(MAX)
= 3.0V
= 500mA
= 150μA
526mW + (3.0V
×
500mA)
=
500mA + 150μA
For a 500mA output current and a 1.2 volt drop
across the AAT3236 at an ambient temperature of
25°C, the maximum on-time duty cycle for the
device would be 87.57%.
The following family of curves show the safe oper-
ating area for duty-cycled operation from ambient
room temperature to the maximum operating level.
Device Duty Cycle vs. V
DROP
(V
OUT
= 2.5V @ 25°C)
3.5
V
IN(MAX)
= 4.05V
From the discussion above, P
D(MAX)
was deter-
mined to equal 526mW at T
A
= 25°C.
Thus, the AAT3236 can sustain a constant 3V output
at a 500mA load current as long as V
IN
is
≤
4.05V at
an ambient temperature of 25°C.
Higher input-to-output voltage differentials can be
obtained with the AAT3236, while maintaining device
functions within 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
= 4.2V
while V
OUT
= 3.0V at a 500mA load and T
A
= 25°C.
V
IN
is greater than 4.05V, which is the maximum
safe continuous input level for V
OUT
= 3.0V at
500mA for T
A
= 25°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
= 150μA
I
OUT
V
IN
= 500mA
= 4.2V
3.5
3
2.5
2
1.5
1
0.5
0
0
Voltage Drop (V)
3
2.5
2
1.5
1
0.5
0
0
10
20
30
40
50
60
70
80
200 mA
500 mA
400 mA
300 mA
90
100
Duty Cycle (%)
Device Duty Cycle vs. V
DROP
(V
OUT
= 2.5V @ 50°C)
3.5
Voltage Drop (V)
3
2.5
2
1.5
1
0.5
0
0
10
20
30
40
50
60
200 mA
500 mA
400 mA
300 mA
100 mA
70
80
90
100
Duty Cycle (%)
Device Duty Cycle vs. V
DROP
(V
OUT
= 2.5V @ 85°C)
V
OUT
= 3.0V
Voltage Drop (V)
P
D(MAX)
%DC = 100
(V
IN
- V
OUT
)I
OUT
+ (V
IN
×
I
GND
)
%DC = 100
526mW
(4.2V - 3.0V)500mA + (4.2V
×
150μA)
100 mA
200 mA
500 mA
400 mA
10
20
%DC = 87.57%
P
D(MAX)
is assumed to be 526mW.
300 mA
30
40
50
60
70
80
90
100
Duty Cycle (%)
12
3236.2007.03.1.4
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
