AAT3220 Datasheet, PDF (12/16 Pages) Advanced Analogic Technologies – 150mA NanoPower™ LDO Linear Regulator

AAT3220
150mA NanoPower™ LDO Linear Regulator
Device Duty Cycle vs. V_DROP
V_OUT = 2.5V @ 25 degrees C
3.5
3
2.5
200mA
2
150mA
1.5
1
0.5
0
0
10 20 30 40 50 60 70 80 90 100
Duty Cycle (%)
Device Duty Cycle vs. V_DROP
V_OUT = 2.5V @ 50 degrees C
3.5
3
2.5
200mA
2
150mA
1.5
1
0.5
0
0
10 20 30 40 50 60 70 80 90 100
Duty Cycle (%)
Device Duty Cycle vs. V_DROP
V_OUT = 2.5V @ 85 degrees C
3.5
3
100mA
2.5
2
1.5
1
0.5
0
0
200mA
150mA
10 20 30 40 50 60 70 80 90 100
Duty Cycle (%)
12
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 calcu-
late the power dissipation at the nominal continu-
ous level, then factor in the addition power dissi-
pation due to the short duration high current peaks.
For example, a 3.0V system using a AAT3220IGV-
2.5-T1 operates at a continuous 100mA load cur-
rent level and has short 150mA current peaks. The
current peak occurs for 378µs out of a 4.61ms peri-
od. It will be assumed the input voltage is 5.0V.
First the current duty cycle percentage must be
calculated:
% Peak Duty Cycle: X/100 = 378µs/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. Next, the continuous
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_D(MAX) = (V_IN - V_OUT)I_OUT + (V_IN x I_GND)
P_D(100mA) = (4.2V - 3.0V)100mA + (4.2V x 1.1µA)
P_D(100mA) = 120mW
P_D(91.8%D/C) = %DC x P_D(100mA)
P_D(91.8%D/C) = 0.918 x 120mW
P_D(91.8%D/C) = 110.2mW
The power dissipation for 100mA load occurring for
91.8% of the duty cycle will be 110.2mW. Now the
power dissipation for the remaining 8.2% of the
duty cycle at the 150mA load can be calculated:
P_D(MAX) = (V_IN - V_OUT)I_OUT + (V_IN x I_GND)
P_D(150mA) = (4.2V - 3.0V)150mA + (4.2V x 1.1µA)
P_D(150mA) = 180mW
P_D(8.2%D/C) = %DC x P_D(150mA)
P_D(8.2%D/C) = 0.082 x 180mW
P_D(8.2%D/C) = 14.8mW
The power dissipation for a 150mA load occurring
for 8.2% of the duty cycle will be 14.8mW. Finally,
the two power dissipation levels can be summed to
determine the total power dissipation under the
varied load.
3220.2001.09.1.0