AAT3215 Datasheet, PDF (12/18 Pages) Advanced Analogic Technologies – 150mA CMOS High Performance LDO

AAT3215
150mA CMOS High Performance LDO
Thus, the AAT3215 can sustain a constant 2.5V out-
put at a 150mA load current as long as V_IN is ≤ 6.00V
at an ambient temperature of 25°C. 6.0V is the
absolute maximum voltage where an AAT3215
would never be operated, thus at 25°C, the device
would not have any thermal concerns or operational
V_IN(MAX) limits.
This situation can be different at 85°C. The follow-
ing is an example for an AAT3215 set for a 2.5V
output at 85°C:
V_OUT
I_OUT
I_GND
= 2.5V
= 150mA
= 150µA
V_IN(MAX)
=
211mW + (2.5V · 150mA)
150mA + 150μA
V_IN(MAX) = 3.90V
From the discussion above, P_D(MAX) was deter-
mined to equal 211mW at T_A = 85°C.
Higher input-to-output voltage differentials can be
obtained with the AAT3215, 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 = 2.5V at a 150mA load and T_A = 85°C.
V_IN is greater than 3.90V, which is the maximum
safe continuous input level for V_OUT = 2.5V at
150mA for T_A = 85°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
I_OUT
V_IN
= 150µA
= 150mA
= 4.2V
V_OUT = 2.5V
%DC =
100
P_D(MAX)
(V_IN - V_OUT)I_OUT + (V_IN · I_GND)
211mW
%DC = 100 _{(4.2V - 2.5V)150mA + (4.2V · 150μA)}
%DC = 85.54%
P_D(MAX) was assumed to be 211mW.
12
For a 150mA output current and a 2.7V drop
across the AAT3215 at an ambient temperature of
85°C, the maximum on-time duty cycle for the
device would be 85.54%.
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
3
2.5
2
1.5
1
0.5
0
0
200mA
10 20 30 40 50 60 70 80 90 100
Duty Cycle (%)
Device Duty Cycle vs. V_DROP
(V_OUT = 2.5V @ 50°C)
3.5
3
2.5
2
1.5
1
0.5
0
0
200mA
150mA
10 20 30 40 50 60 70 80 90 100
Duty Cycle (%)
Device Duty Cycle vs. V_DROP
(V_OUT = 2.5V @ 85°C)
3.5
3
2.5
2
1.5
1
0.5
0
0
200mA
150mA
100mA
10 20 30 40 50 60 70 80 90 100
Duty Cycle (%)
3215.2006.05.1.6