ALXYY ANALOGICTECH [Advanced Analogic Technologies], ALXYY Datasheet - Page 12

• Manufacturer Part Number: ALXYY
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

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 operating
area for duty-cycled operation from ambient room tem-
perature to the maximum operating level.
12
PowerLinear
3.5
2.5
1.5
0.5
3.5
2.5
1.5
0.5
3.5
2.5
1.5
0.5
3
2
1
0
3
2
1
0
3
2
1
0
0
0
0
10
10
Device Duty Cycle vs. V
10
Device Duty Cycle vs. V
Device Duty Cycle vs. V
TM
20
20
20
(V
(V
OUT
(V
30
30
30
OUT
OUT
= 2.5V @ 50°C)
Duty Cycle (%)
Duty Cycle (%)
Duty Cycle (%)
40
40
40
= 2.5V @ 25°C)
= 2.5V @ 85°C)
200mA
50
50
50
60
60
60
200mA
150mA
70
70
70
DROP
100mA
DROP
DROP
80
80
150mA
80
200mA
90
90
90
w w w . a n a l o g i c t e c h . c o m
100
100
100
150mA NanoPower™ LDO Linear Regulator
High Peak Output Current Applications
Some applications require the LDO regulator to operate
at continuous nominal levels with short duration, high-
current peaks. The duty cycles for both output current
levels must be taken into account. To do so, one would
first need to calculate the power dissipation at the nom-
inal continuous level, then factor in the addition power
dissipation due to the short duration, high-current
peaks.
For example, a 2.5V system using an AAT3221/
2IGV-2.5-T1 operates at a continuous 100mA load cur-
rent level and has short 150mA current peaks. The cur-
rent peak occurs for 378μs out of a 4.61ms period. It
will be assumed the input voltage is 5.0V.
First, the current duty cycle percentage must be
calculated:
% Peak Duty Cycle: X/100 = 378ms/4.61ms
% Peak Duty Cycle = 8.2%
The LDO regulator will be under the 100mA load for
91.8% of the 4.61ms period and have 150mA peaks
occurring for 8.2% of the time.
nominal power dissipation for the 100mA load should be
determined then multiplied by the duty cycle to conclude
the actual power dissipation over time.
P
P
P
P
P
P
The power dissipation for a 100mA load occurring for
91.8% of the duty cycle will be 229.5mW.
power dissipation for the remaining 8.2% of the duty
cycle at the 150mA load can be calculated:
P
P
P
P
P
P
D(MAX)
D(100mA)
D(100mA)
D(91.8%D/C)
D(91.8%D/C)
D(91.8%D/C)
D(MAX)
D(150mA)
D(150mA)
D(8.2%D/C)
D(8.2%D/C)
D(8.2%D/C)
= (V
= (V
= (5.0V - 2.5V)100mA + (5.0V · 1.1mA)
= 250mW
= (5.0V - 2.5V)150mA + (5.0V · 1.1mA)
= 375mW
= %DC · P
= 0.082 · 375mW
= 30.75mW
= %DC · P
= 0.918 · 250mW
= 229.5mW
IN
IN
- V
- V
OUT
OUT
)I
)I
D(150mA)
OUT
OUT
D(100mA)
PRODUCT DATASHEET
+ (V
+ (V
AAT3221/2
IN
IN
· I
· I
GND
GND
)
)
Next, the continuous
3221.2007.11.1.12
Now the