AAT3236
300mA CMOS High Performance LDO
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%.
VOUT
IOUT
IGND
= 3.0V
= 500mA
= 150μA
The following family of curves show the safe oper-
ating area for duty-cycled operation from ambient
room temperature to the maximum operating level.
526mW + (3.0V × 500mA)
VIN(MAX)
=
500mA + 150μA
VIN(MAX) = 4.05V
Device Duty Cycle vs. VDROP
(VOUT = 2.5V @ 25°C)
From the discussion above, PD(MAX) was deter-
mined to equal 526mW at TA = 25°C.
3.5
200 mA
3
500 mA
2.5
Thus, the AAT3236 can sustain a constant 3V output
at a 500mA load current as long as VIN is ≤ 4.05V at
an ambient temperature of 25°C.
2
400 mA
1.5
1
300 mA
0.5
0
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.
0
10
20
30
40
50
60
70
80
90
100
Duty Cycle (%)
Device Duty Cycle vs. VDROP
(VOUT = 2.5V @ 50°C)
For example, an application requires VIN = 4.2V
while VOUT = 3.0V at a 500mA load and TA = 25°C.
VIN is greater than 4.05V, which is the maximum
safe continuous input level for VOUT = 3.0V at
500mA for TA = 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:
3.5
200 mA
3
2.5
2
100 mA
500 mA
400 mA
1.5
1
300 mA
0.5
0
0
10
20
30
40
50
60
70
80
90
100
IGND = 150μA
IOUT = 500mA
VIN = 4.2V
VOUT = 3.0V
Duty Cycle (%)
Device Duty Cycle vs. VDROP
(VOUT = 2.5V @ 85°C)
3.5
3
100 mA
PD(MAX)
2.5
2
%DC = 100
(VIN - VOUT)IOUT + (VIN × IGND
)
200 mA
1.5
1
526mW
(4.2V - 3.0V)500mA + (4.2V × 150μA)
%DC = 100
500 mA
400 mA
0.5
0
300 mA
%DC = 87.57%
0
10
20
30
40
50
60
70
80
90
100
PD(MAX) is assumed to be 526mW.
Duty Cycle (%)
12
3236.2007.03.1.4
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
