AAT3216 Datasheet, PDF (13/16 Pages) List of Unclassifed Manufacturers – 150mA MicroPower™ LDO with PowerOK

AAT3216
150mA MicroPower™ LDO with PowerOK
High Peak Output Current Applications
Some applications require the LDO regulator to
operate at continuous nominal level 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 additional power dissi-
pation due to the short duration, high-current
peaks.
For example, a 2.5V system using a AAT3216IGV-
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 4.2V.
First, the current duty cycle in percent 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 dis-
sipation over time.
P_D(MAX) = (V_IN - V_OUT)I_OUT + (V_IN x I_GND)
P_D(100mA) = (4.2V - 2.5V)100mA + (4.2V x 150µA)
P_D(100mA) = 170.6mW
P_D(91.8%D/C) = %DC x P_D(100mA)
P_D(91.8%D/C) = 0.918 x 170.6mW
P_D(91.8%D/C) = 156.6mW
The power dissipation for 100mA load occurring for
91.8% of the duty cycle will be 156.6mW. 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 - 2.5V)150mA + (4.2V x 150mA)
P_D(150mA) = 255.6mW
P_D(8.2%D/C) = %DC x P_D(150mA)
P_D(8.2%D/C) = 0.082 x 255.6mW
P_D(8.2%D/C) = 21mW
The power dissipation for 150mA load occurring for
8.2% of the duty cycle will be 21mW. Finally, the
two power dissipation levels can summed to deter-
mine the total true power dissipation under the var-
ied load.
P_D(total) = P_D(100mA) + P_D(150mA)
P_D(total) = 156.6mW + 21mW
P_D(total) = 177.6mW
The maximum power dissipation for the AAT3216
operating at an ambient temperature of 85°C is
211mW. The device in this example will have a total
power dissipation of 177.6mW. This is well within
the thermal limits for safe operation of the device.
3216.2006.01.1.3
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