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AAT3221/2
150mA NanoPower™ LDO Linear Regulator
General Description
The AAT3221 and AAT3222 PowerLinear™
NanoPower Low Dropout Linear Regulators are
ideal for portable applications where extended battery life is critical. This device features extremely
low quiescent current which is typically 1.1µA.
Dropout voltage is also very low, typically less than
200mV at the maximum output current of 150mA.
The AAT3221/2 has an Enable pin feature, which
when asserted will enter the LDO regulator into a
shutdown mode removing power from its load and
offering extended power conservation capabilities
for portable battery powered applications.
The AAT3221/2 has output short circuit and over
current protection. In addition, the device also has
an over temperature protection circuit, which will
shutdown the LDO regulator during extended overcurrent events. It is available with active high or
active low enable input.
The AAT3221 and AAT3222 are available in space
saving 5-pin SOT23 packages. The AAT3221 is
also available in the 8-pin SC70JW package. The
device is rated over a -40°C to 85°C temperature
range. Since only a small, 1µF ceramic output
capacitor is recommended, often the only space
used is that occupied by the AAT3221/2 itself. The
AAT3221/2 is truly a compact and cost effective voltage conversion solution.
PowerLinear
Features
• 1.1 µA Quiescent Current
• Low Dropout: 200 mV (typical)
• Guaranteed 150 mA Output
• High accuracy: ±2%
• Current limit protection
• Over-Temperature protection
• Extremely Low power shutdown mode
• Low Temperature Coefficient
• Factory programmed output voltages
• 1.8V to 3.5V
• Stable operation with virtually any output
capacitor type
• Active high or low Enable pin
• 5-pin SOT23 or 8-pin SC70JW packages
• 4kV ESD
Applications
• Cellular Phones
• Notebook Computers
• Portable Communication Devices
• Handheld Electronics
• Remote Controls
• Digital Cameras
• PDAs
™
Preliminary Information
The AAT3221/2 is similar to the AAT3220 with the
exception that it offers further power savings with
its enable pin.
Typical Application
INPUT
IN
OUT
AAT3221/2
ENABLE
C
IN
1µF
3221.2002.03.0.94 1
(ENABLE)
EN
(EN)
GND
C
1µF
OUT
OUTPUT
GNDGND
AAT3221/2
150mA NanoPower™ LDO Linear Regulator
Pin Descriptions
Pin #
AAT3221
SOT23-5 SC70JW-8
1 2 2 IN Input pin
2 5, 6, 7, 8 1 GND Ground connection pin
3 4 5 EN (EN) Enable Input. Logic compatible enable with
4 3 4 NC Not Connected
5 1 3 OUT Output pin - should be decoupled with 1µF or
AAT3222
Symbol Function
active high or active low option available; see
Ordering Information and Applications
Information for details.
greater capacitor
Pin Configuration
AAT3221 AAT3221 AAT3222
SOT23-5 SC70JW-8 SOT23-5
(Top View) (Top View) (Top View)
IN
GND
(EN) EN
1
2
3
5
OUT
4
NC
OUT
IN
NC
(EN) EN
1 2
1
2
3
4
8
7
6
5
GND
GND
GND
GND
GND
OUT
IN
1
2
3
5
EN (EN)
4
NC
2 3221.2002.03.0.94
AAT3221/2
150mA NanoPower™ LDO Linear Regulator
Absolute Maximum Ratings (T
=25°C unless otherwise noted)
A
Symbol Description Value Units
V
IN
V
EN
V
ENIN(MAX)
I
OUT
T
J
T
LEAD
Note: Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum rating should be applied at any one time.
Input Voltage -0.3 to 6 V
EN (EN) to GND Voltage -0.3 to 6 V
Maximum EN (EN) to Input Voltage 0.3 V
Maximum DC Output Current PD/(VIN-VO)mA
Operating Junction Temperature Range -40 to 150 °C
Maximum Soldering Temperature (at leads, 10 sec) 300 °C
Thermal Information
Symbol Description Rating Units
Θ
JA
P
D
Note 1: Mounted on a demo board.
Thermal Resistance (SOT23-5 or SC70JW-8)
Power Dissipation (SOT23-5 or SC70JW-8)
1
1
150 °C/W
667 mW
Recommended Operating Conditions
Symbol Description Rating Units
V
IN
T Ambient Temperature Range -40 to +85 °C
Input Voltage (V
+0.34) to 5.5 V
OUT
3221.2002.03.0.94 3
AAT3221/2
150mA NanoPower™ LDO Linear Regulator
Electrical Characteristics (V
IN=VOUT(NOM)
+1V, I
=1mA, C
OUT
=1µF, TA=25°C unless otherwise noted)
OUT
Symbol Description Conditions Min Typ Max Units
V
∆V
OUT/VOUT
∆V
OUT/VOUT
V
V
I
EN(SINK)
OUT
I
OUT
I
SC
I
Q
I
SD
V
DO
EN(L)
EN(H)
DC Output Voltage Tolerance
Output Current V
Short Circuit Current V
V
=2.8V -1.4 1.4
OUT
> 1.2 V 150 mA
OUT
< 0.4 V 350 mA
OUT
Ground Current VIN= 5 V, no load 1.1 2.5 µA
Shutdown Current EN = inactive 20 nA
Line Regulation VIN= 4.0-5.5 V 0.15 0.4 %/V
V
= 1.8 1.0 1.65
OUT
V
= 2.0 0.9 1.58
OUT
V
= 2.3 0.8 1.45
OUT
V
= 2.4 0.8 1.40
OUT
V
= 2.5 0.8 1.35
OUT
Load Regulation IL=1 to 100mA V
Dropout Voltage
1
I
= 100mA V
OUT
= 2.7 0.7 1.25 %
OUT
V
= 2.8 0.7 1.20
OUT
V
= 2.85 0.7 1.20
OUT
V
= 3.0 0.6 1.15
OUT
V
= 3.3 0.5 1.00
OUT
V
= 3.5 0.5 1.00
OUT
V
= 1.8 290 340
OUT
V
= 2.0 265 315
OUT
V
= 2.3 230 275
OUT
V
= 2.4 220 265
OUT
V
= 2.5 210 255
OUT
= 2.7 200 240 mV
OUT
V
= 2.8 190 235
OUT
V
= 2.85 190 230
OUT
V
= 3.0 190 225
OUT
V
= 3.3 180 220
OUT
V
= 3.5 180 220
OUT
EN Input Low Voltage 0.8 V
V
= 2.7 V to 3.6 V 2.0 V
EN Input High Voltage
IN
VIN= 5 V 2.4 V
EN Input leakage VON= 5.5 V 0.01 1 µA
PSRR Power Supply Rejection Ratio 100 Hz 50 dB
T
SD
T
HYS
e
N
T
C
Note 1: VDOis defined as VIN- V
Over Temp Shutdown Threshold 140 °C
Over Temp Shutdown Hysteresis 20 °C
Output Noise 350 µV
Output Voltage Temp. Coefficient 80 PPM/°C
OUT
when V
is 98% of nominal.
OUT
-2.0 2.0
%
RMS
4 3221.2002.03.0.94
Typical Characteristics
AAT3221/2
150mA NanoPower LDO Linear Regulator
(Unless otherwise noted, VIN= V
+ 1V, TA= 25 C, C
OUT
Output Voltage vs. Output Current
3.03
3.02
3.01
3
2.99
Output (V)
2.98
2.97
020406080100
25°C
80°C
Output (m A)
Output Voltage vs. Input Voltage
3.03
3.02
3.01
Output (V)
3
1mA
10mA
40mA
-30°C
= 5.6 F ceramic, I
OUT
Output Voltage v. Input Voltage
3.1
3
2.9
2.8
2.7
Output (V)
2.6
2.5
2.7 2.9 3.1 3.3 3.5
Drop-out Voltage vs. Output Current
40 0
300
200
100
Drop-out (mV )
1mA
= 100mA)
OUT
40mA
10mA
Input (V)
80°C
25°C
-30°C
2.99
3.5 4 4.5 5 5.5
Input (V )
Supply Current vs. Input Voltage
5
4
3
2
1
Input (µA) with No Load
0
012 3 456
80°C
-30°C
Input ( V)
25°C
0
0255075100125150
Output (mA)
PSRR with 10mA Load
60
40
20
PSRR (dB)
0
1.E+01 1.E+02 1.E+03 1.E+04 1.E+05
Frequency (Hz)
3221.2002.03.0.94 5
AAT3221/2
150mA NanoPower™ LDO Linear Regulator
(Unless otherwise noted, VIN= V
+ 1V, TA= 25°C, C
OUT
Noise Spectrum
30
20
10
0
-10
-20
Noise (dB µV/rt Hz )
-30
1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06
Frequency (Hz)
Line Response with 10mA Load
3.8
3.6
3.4
3.2
3
Output Voltage ( V )
2.8
2.6
-20 0 0 200 400 600 800
Input
Output
Time (µs)
= 5.6µF ceramic, I
OUT
= 100mA)
OUT
Line Response with 1mA Load
3.8
3.6
Input
3.4
3.2
3
Output
2.8
Output Voltage ( V )
2.6
-200 0 200 400 600 800
Time (µs)
6
5
4
3
2
1
Input Voltage ( V )
0
Line Response with 100mA Load
6
5
4
3
2
1
Input Voltage ( V )
0
3.8
3.6
3.4
3.2
3
2.8
Output Voltage ( V )
2.6
-200 0 200 400 600 800
Input
Output
Time (µs)
6
5
4
3
2
1
Input Voltage ( V )
0
Load Transient - 1 mA / 40 mA
4
3
Output
Output (V)
2
-10 123
Time (ms)
320
240
160
80
0
Output (mA)
Output (V)
Load Transient - 1 mA / 80 mA
4
Output
3
2
-10 12 3
Time (ms)
320
240
160
80
0
6 3221.2002.03.0.94
Output (mA)
AAT3221/2
150mA NanoPower™ LDO Linear Regulator
(Unless otherwise noted, V
= V
IN
+ 1V, TA= 25°C, C
OUT
Power Up with 1mA Load
4
3
Enable
2
Output (V)
1
Output
0
-10 12
Time (ms)
Power Up with 10mA Load
4
3
Enable
2
Output (V)
1
Output
0
-10 12
Time (ms)
= 5.6µF ceramic, I
OUT
= 100mA)
OUT
Turn On with 1mA Load
5
4
3
2
1
0
Input ( V )
-1
-2
-3
4
3
3
2
Enable
2
Output (V)
1
1
Enable ( V )
0
Output
0
-10 1 2
-1
Time (ms)
Turn On with 10mA Load
5
4
3
2
1
0
Input ( V )
-1
-2
-3
4
3
2
Output (V)
1
Enable
3
2
1
Enable (V )
0
Output
0
-10 1 2
-1
Time (ms)
Power Up with 100mA Load
4
3
2
Enable
Output (V)
1
Output
0
-10 12
Time (ms)
5
4
3
2
1
0
-1
-2
-3
4
3
2
Input ( V)
Output (V)
0
Turn On with 100mA Load
3
2
Enable
1
Output
-10 1 2
Time (ms)
1
0
-1
3221.2002.03.0.94 7
Enable (V )
Functional Block Diagram
AAT3221/2
150mA NanoPower™ LDO Linear Regulator
IN
EN
Over-Current
Protection
Over-Temp
Protection
V
REF
OUT
GND
Functional Description
The AAT3221 and AAT3222 are intended for LDO
regulator applications where output current load
requirements range from No Load to 150mA. The
advanced circuit design of the AAT3221/2 has been
optimized for very low quiescent or ground current
consumption making it ideal for use in power management systems for small battery operated
devices. The typical quiescent current level is just
1.1µA. The AAT3221/2 also contains an enable circuit, which has been provided to shutdown the LDO
regulator for additional power conservation in
portable products. In the shutdown state the LDO
draws less than 1µA from input supply.
The LDO also demonstrates excellent power supply ripple rejection (PSRR), and load and line transient response characteristics. The AAT3221/2 is a
8 3221.2002.03.0.94
truly high performance LDO regulator especially
well suited for circuit applications which are sensitive to load circuit power consumption and extended battery life.
The LDO regulator output has been specifically
optimized to function with low cost, low ESR
ceramic capacitors. However, the design will allow
for operation with a wide range of capacitor types.
The AAT3221/2 has complete short circuit and
thermal protection. The integral combination of
these two internal protection circuits give the
AAT3221/2 a comprehensive safety system to
guard against extreme adverse operating conditions. Device power dissipation is limited to the
package type and thermal dissipation properties.
Refer to the thermal considerations section for
details on device operation at maximum output
load levels.
AAT3221/2
150mA NanoPower™ LDO Linear Regulator
Applications Information
To assure the maximum possible performance is
obtained from the AAT3221/2, please refer to the
following application recommendations.
Input Capacitor
Typically a 1µF or larger capacitor is recommended
for CINin most applications. A CINcapacitor is not
required for basic LDO regulator operation.
However, if the AAT3221/2 is physically located any
distance more than a centimeter or two from the
input power source, a CINcapacitor will be needed
for stable operation. CINshould be located as close
to the device VINpin as practically possible. CINvalues greater than 1µF will offer superior input line
transient response and will assist in maximizing the
power supply ripple rejection.
Ceramic, tantalum or aluminum electrolytic capacitors may be selected for CINas there is no specific
capacitor ESR requirement. For 150mA LDO regulator output operation, ceramic capacitors are recommended for CINdue to their inherent capability
over tantalum capacitors to withstand input current
surges from low impedance sources such as batteries in portable devices.
Output Capacitor
For proper load voltage regulation and operational
stability, a capacitor is required between pins V
and GND. The C
LDO regulator ground pin should be made as direct
as practically possible for maximum device performance. The AAT3221/2 has been specifically
designed to function with very low ESR ceramic
capacitors. Although the device is intended to operate with these low ESR capacitors, it is stable over
a very wide range of capacitor ESR, thus it will also
work with some higher ESR tantalum or aluminum
electrolytic capacitors. However, for best performance, ceramic capacitors are recommended.
The value of C
10µF, however 1µF is sufficient for most operating
conditions.
If large output current steps are required by an
application, then an increased value for C
should be considered. The amount of capacitance
needed can be calculated from the step size of the
change in output load current expected and the
voltage excursion that the load can tolerate.
OUT
capacitor connection to the
OUT
typically ranges from 0.47µF to
OUT
OUT
The total output capacitance required can be calculated using the following formula:
OUT
=
∆I
∆V
× 15µF
C
Where:
∆I = maximum step in output current
∆V = maximum excursion in voltage that the load
can tolerate
Note that use of this equation results in capacitor
values approximately two to four times the typical
value needed for an AAT3221/2 at room temperature. The increased capacitor value is recommended if tight output tolerances must be maintained over
extreme operating conditions and maximum operational temperature excursions. If tantalum or aluminum electrolytic capacitors are used, the capacitor
value should be increased to compensate for the
substantial ESR inherent to these capacitor types.
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use
with the AAT3221/2. Ceramic capacitors offer
many advantages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very low ESR, is lower cost, has a
smaller PCB footprint and is non-polarized. Line
and load transient response of the LDO regulator is
improved by using low ESR ceramic capacitors.
Since ceramic capacitors are non-polarized, they
are less prone to damage if connected incorrectly.
Equivalent Series Resistance (ESR): ESR is a
very important characteristic to consider when
selecting a capacitor. ESR is the internal series
resistance associated with a capacitor, which
includes lead resistance, internal connections,
capacitor size and area, material composition and
ambient temperature. Typically capacitor ESR is
measured in milliohms for ceramic capacitors and
can range to more than several ohms for tantalum
or aluminum electrolytic capacitors.
Ceramic Capacitor Materials: Ceramic capacitors
less than 0.1µF are typically made from NPO or
COG materials. NPO and COG materials are typically tight tolerance and very stable over temperature. Larger capacitor values are typically composed
of X7R, X5R, Z5U and Y5V dielectric materials.
3221.2002.03.0.94 9
AAT3221/2
150mA NanoPower™ LDO Linear Regulator
Large ceramic capacitors, typically greater than
2.2µF are often available in the low cost Y5V and Z5U
dielectrics. These two material types are not recommended for use with LDO regulators since the capacitor tolerance can vary more than ±50% over the
operating temperature range of the device. A 2.2µF
Y5V capacitor could be reduced to 1µF over the full
operating temperature range. This can cause problems for circuit operation and stability. X7R and X5R
dielectrics are much more desirable. The temperature tolerance of X7R dielectric is better than ±15%.
Capacitor area is another contributor to ESR.
Capacitors, which are physically large in size will
have a lower ESR when compared to a smaller
sized capacitor of equivalent material and capacitance value. These larger devices can also improve
circuit transient response when compared to an
equal value capacitor in a smaller package size.
Consult capacitor vendor data sheets carefully when
selecting capacitors for use with LDO regulators.
Enable Function
The AAT3221/2 features an LDO regulator enable /
disable function. This pin (EN) is compatible with
CMOS logic. Active high or active low options are
available (see Ordering Information). For a logic high
signal, the EN control level must be greater then 2.4
volts. A logic low signal is asserted when the voltage
on the EN pin falls below 0.6 volts. For example, the
active high version 3221/2 will turn on when a logic
high is applied to the EN pin. If the enable function is
not needed in a specific application, it may be tied to
the respective voltage level to keep the LDO regulator in a continuously on state; e.g. the active high version 3221/2 will tie VINto EN to remain on.
Short Circuit Protection and Thermal
Protection
The AAT3221/2 is protected by both current limit
and over temperature protection circuitry. The
internal short circuit current limit is designed to activate when the output load demand exceeds the
maximum rated output. If a short circuit condition
were to continually draw more than the current limit
threshold, the LDO regulator's output voltage will
drop to a level necessary to supply the current
demanded by the load. Under short circuit or other
over current operating conditions, the output voltage will drop and the AAT3221/2's die temperature
will increase rapidly. Once the regulator's power
dissipation capacity has been exceeded and the
internal die temperature reaches approximately
140°C the system thermal protection circuit will
become active. The internal thermal protection circuit will actively turn off the LDO regulator output
pass device to prevent the possibility of over temperature damage. The LDO regulator output will
remain in a shutdown state until the internal die
temperature falls back below the 140°C trip point.
The interaction between the short circuit and thermal protection systems allow the LDO regulator to
withstand indefinite short circuit conditions without
sustaining permanent damage.
No-Load Stability
The AAT3221/2 is designed to maintain output voltage regulation and stability under operational noload conditions. This is an important characteristic
for applications where the output current may drop
to zero. An output capacitor is required for stability
under no load operating conditions. Refer to the
output capacitor considerations section for recommended typical output capacitor values.
Thermal Considerations and High
Output Current Applications
The AAT3221/2 is designed to deliver a continuous
output load current of 150mA under normal operating conditions. The limiting characteristic for the
maximum output load safe operating area is essentially package power dissipation and the internal preset thermal limit of the device. In order to obtain high
operating currents, careful device layout and circuit
operating conditions need to be taken into account.
The following discussions will assume the LDO regulator is mounted on a printed circuit board utilizing
the minimum recommended footprint and the printed circuit board is 0.062inch thick FR4 material with
one ounce copper.
At any given ambient temperature (TA) the maximum package power dissipation can be determined by the following equation:
P
Constants for the AAT3221/2 are T
mum junction temperature for the device which is
125°C and Θ
resistance. Typically, maximum conditions are calculated at the maximum operating temperature
where TA= 85°C, under normal ambient conditions
= [T
D(MAX)
= 150°C/W, the package thermal
JA
J(MAX)
- T
] / Θ
A
JA
J(MAX)
, the maxi-
10 3221.2002.03.0.94
150mA NanoPower™ LDO Linear Regulator
T
= 25°C. Given TA= 85°, the maximum package
A
power dissipation is 267mW. At TA= 25°C°, the
maximum package power dissipation is 667mW.
The maximum continuous output current for the
AAT3221/2 is a function of the package power dissipation and the input to output voltage drop across
the LDO regulator. Refer to the following simple
equation:
I
OUT(MAX)
For example, if VIN= 5V, V
I
OUT(MAX)
< 267mA. The output short circuit protection threshold is set between 150mA and 300mA. If
the output load current were to exceed 267mA or if
the ambient temperature were to increase, the internal die temperature will increase. If the condition
remained constant and the short circuit protection
did not activate, there would be a potential damage
hazard to LDO regulator since the thermal protection
circuit will only activate after a short circuit event
occurs on the LDO regulator output.
To figure what the maximum input voltage would be
for a given load current refer to the following equation. This calculation accounts for the total power
dissipation of the LDO Regulator, including that
caused by ground current.
P
D(MAX)
This formula can be solved for VIN to determine
the maximum input voltage.
V
IN(MAX)
= (P
The following is an example for an AAT3221/2 set
for a 2.5 volt output:
From the discussion above, P
mined to equal 667mW at TA= 25°C.
V
= 2.5 volts
OUT
I
= 150mA
OUT
I
= 1.1µA
GND
V
V
=(667mW+(2.5Vx150mA))/(150mA +1.1µA)
IN(MAX)
IN(MAX)
= 6.95V
Thus, the AAT3221/2 can sustain a constant 2.5V
output at a 150mA load current as long as V
6.95V at an ambient temperature of 25°C. 5.5V is
the maximum input operating voltage for the
< P
= (VIN- V
+ (V
D(MAX)
D(MAX)
OUT
OUT)IOUT
OUT
/ (VIN- V
OUT
)
= 2.5V and TA= 25°,
x I
OUT
+ (VINx I
)) / (I
D(MAX)
)
GND
+ I
OUT
was deter-
GND
IN
)
is ≤
AAT3221/2
AAT3221/2, thus at 25°C, the device would not have
any thermal concerns or operational V
This situation can be different at 85°C. The following is an example for an AAT3221/2 set for a 2.5
volt output at 85°C:
From the discussion above, P
D(MAX)
mined to equal 267mW at TA= 85°C.
V
= 2.5 volts
OUT
I
= 150mA
OUT
I
= 1.1µA
GND
V
V
=(267mW+(2.5Vx150mA))/(150mA +1.1µA)
IN(MAX)
= 4.28V
IN(MAX)
Higher input to output voltage differentials can be
obtained with the AAT3221/2, while maintaining
device functions in 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 VIN= 5.0V
while V
= 2.5V at a 150mA load and TA= 85°C.
OUT
VINis greater than 4.28V, which is the maximum
safe continuous input level for V
OUT
150mA for TA= 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:
P
I
GND
I
OUT
is assumed to be 267mW
D(MAX)
= 1.1µA
= 150mA
VIN= 5.0 volts
V
= 2.5 volts
OUT
%DC = 100(P
D(MAX)
/ ((VIN- V
OUT)IOUT
+ (VINx I
%DC=100(267mW/((5.0V-2.5V)150mA+(5.0Vx1.1µA))
%DC = 71.2%
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 temperature to the maximum operating level.
limits.
IN(MAX)
was deter-
= 2.5V at
GND
))
3221.2002.03.0.94 11
AAT3221/2
150mA NanoPower™ LDO Linear Regulator
Device Duty Cycle vs. V
V
= 2.5V @ 25 degrees C
OUT
3.5
3
2.5
2
1.5
1
0.5
Voltage Drop (V)
0
0 102030405060708090100
Duty Cycle (%)
Device Duty Cycle vs. V
V
= 2.5V @ 50 degrees C
OUT
3.5
3
2.5
2
1.5
1
0.5
Voltage Drop (V)
0
0 102030405060708090100
Duty Cycle (%)
DROP
200mA
DROP
200mA
150mA
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 nominal continuous level, then factor in the addition power dissipation due to the short duration high current peaks.
For example, a 2.5V system using a AAT3221/
2IGV-2.5-T1 operates at a continuous 100mA load
current level and has short 150mA current peaks.
The current 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. 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
P
P
P
P
P
= (VIN- V
D(MAX)
D(100mA)
D(100mA)
D(91.8%D/C)
D(91.8%D/C)
D(91.8%D/C)
OUT)IOUT
+ (VINx I
GND
)
= (5.0V - 2.5V)100mA + (5.0V x 1.1mA)
= 250mW
= %DC x P
D(100mA)
= 0.918 x 250mW
= 229.5mW
Device Duty Cycle vs. V
V
= 2.5V @ 85 degrees C
OUT
3.5
3
2.5
2
1.5
1
0.5
Voltage Drop (V)
0
0 10 20304050607080 90100
200mA
Duty Cycle (%)
DROP
100mA
150mA
12 3221.2002.03.0.94
AAT3221/2
150mA NanoPower™ LDO Linear Regulator
The power dissipation for a 100mA load occurring
for 91.8% of the duty cycle will be 229.5mW. Now
the power dissipation for the remaining 8.2% of the
duty cycle at the 150mA load can be calculated:
P
P
P
P
P
P
= (VIN- V
D(MAX)
D(150mA)
D(150mA)
D(8.2%D/C)
D(8.2%D/C)
D(8.2%D/C)
OUT)IOUT
+ (VINx I
GND
)
= (5.0V - 2.5V)150mA + (5.0V x 1.1mA)
= 375mW
= %DC x P
D(150mA)
= 0.082 x 375mW
= 30.75mW
The power dissipation for a 150mA load occurring
for 8.2% of the duty cycle will be 20.9mW. Finally,
the two power dissipation levels can summed to
determine the total true power dissipation under the
varied load.
P
P
P
= P
D(total)
D(total)
D(total)
D(100mA)
= 229.5mW + 30.75mW
= 260.25mW
+ P
D(150mA)
The maximum power dissipation for the AAT3221/2
operating at an ambient temperature of 85°C is
267mW. The device in this example will have a total
power dissipation of 260.25mW. This is within the
thermal limits for safe operation of the device.
Printed Circuit Board Layout
Recommendations
In order to obtain the maximum performance from
the AAT3221/2 LDO regulator, very careful attention
must be considered in regard to the printed circuit
board layout. If grounding connections are not properly made, power supply ripple rejection and LDO
regulator transient response can be compromised.
The LDO Regulator external capacitors CINand
C
should be connected as directly as possible
OUT
to the ground pin of the LDO Regulator. For maximum performance with the AAT3221/2, the ground
pin connection should then be made directly back
to the ground or common of the source power supply. If a direct ground return path is not possible
due to printed circuit board layout limitations, the
LDO ground pin should then be connected to the
common ground plane in the application layout.
3221.2002.03.0.94 13
Ordering Information
AAT3221/2
150mA NanoPower™ LDO Linear Regulator
Output Voltage Enable Package Marking
1.8V Active high SOT23-5 N/A AAT3221IGV-1.8-T1
2.0V Active high SOT23-5 N/A AAT3221IGV-2.0-T1
2.3V Active high SOT23-5 N/A AAT3221IGV-2.3-T1
2.4V Active high SOT23-5 N/A AAT3221IGV-2.4-T1
2.5V Active high SOT23-5 N/A AAT3221IGV-2.5-T1
2.7V Active high SOT23-5 N/A AAT3221IGV-2.7-T1
2.8V Active high SOT23-5 N/A AAT3221IGV-2.8-T1
2.85V Active high SOT23-5 N/A AAT3221IGV-2.85-T1
3.0V Active high SOT23-5 N/A AAT3221IGV-3.0-T1
3.3V Active high SOT23-5 N/A AAT3221IGV-3.3-T1
3.5V Active high SOT23-5 N/A AAT3221IGV-3.5-T1
1.8V Active high SC70JW-8 N/A AAT3221IJS-1.8-T1
2.0V Active high SC70JW-8 N/A AAT3221IJS-2.0-T1
2.3V Active high SC70JW-8 N/A AAT3221IJS-2.3-T1
2.4V Active high SC70JW-8 N/A AAT3221IJS-2.4-T1
2.5V Active high SC70JW-8 N/A AAT3221IJS-2.5-T1
2.7V Active high SC70JW-8 N/A AAT3221IJS-2.7-T1
2.8V Active high SC70JW-8 N/A AAT3221IJS-2.8-T1
2.85V Active high SC70JW-8 N/A AAT3221IJS-2.85-T1
3.0V Active high SC70JW-8 N/A AAT3221IJS-3.0-T1
3.3V Active high SC70JW-8 N/A AAT3221IJS-3.3-T1
3.5V Active high SC70JW-8 N/A AAT3221IJS-3.5-T1
1.8V Active high SOT23-5 N/A AAT3222IGV-1.8-T1
1.8V Active high SOT23-5 N/A AAT3222IGV-1.8-T1
2.0V Active high SOT23-5 N/A AAT3222IGV-2.0-T1
2.3V Active high SOT23-5 N/A AAT3222IGV-2.3-T1
2.4V Active high SOT23-5 N/A AAT3222IGV-2.4-T1
2.5V Active high SOT23-5 N/A AAT3222IGV-2.5-T1
2.7V Active high SOT23-5 N/A AAT3222IGV-2.7-T1
2.8V Active high SOT23-5 N/A AAT3222IGV-2.8-T1
2.85V Active high SOT23-5 N/A AAT3222IGV-2.85-T1
3.0V Active high SOT23-5 N/A AAT3222IGV-3.0-T1
3.3V Active high SOT23-5 N/A AAT3222IGV-3.3-T1
3.5V Active high SOT23-5 N/A AAT3222IGV-3.5-T1
2.8V Active low SOT23-5 N/A AAT3221IGV-2.8-2 T1
Part Number
Bulk Tape and Reel
14 3221.2002.03.0.94
Package Information
SOT23-5
AAT3221/2
150mA NanoPower™ LDO Linear Regulator
S1
S
e
D
b
SC70JW-8
eee
D
Dim
Millimeters Inches
Min Max Min Max
A 0.95 1.45 0.037 0.057
A1 0.05 0.15 0.002 0.006
H
E
A2 0.90 1.30 0.035 0.051
b 0.35 0.50 0.014 0.019
c 0.08 0.20 0.003 0.078
D 2.84 3.00 0.112 0.112
E 1.50 1.70 0.059 0.067
e 1.90 0.0748
H 2.60 3.00 0.102 0.118
A
A1
L
c
L 0.35 0.55 .0137 .0216
S 0.47 0.55 0.019 .0216
S1 .95 0.037
Θ 0° 10° 0° 10°
Dim
Millimeters Inches
Min Max Min Max
E 2.10 BSC 0.083 BSC
E1 1.75 2.00 0.069 0.079
E
L 0.23 0.40 0.009 0.016
A 1.10 0.043
A1 0 0.10 0.004
A2 0.70 1.00 0.028 0.039
D 2.00 BSC 0.079 BSC
b
0.048REF
c
A2
A
e 0.50 BSC 0.020 BSC
b 0.15 0.30 0.006 0.012
c 0.10 0.20 0.004 0.008
Θ 08º08º
Θ1 4º 10º 4º 10º
Θ1
3221.2002.03.0.94 15
L
Θ
E1
A1
AAT3221/2
150mA NanoPower™ LDO Linear Regulator
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Advanced Analogic Technologies, Inc.
1250 Oakmead Parkway, Suite 310, Sunnyvale, CA 94086
Phone (408) 524-9684
Fax (408) 524-9689
16 3221.2002.03.0.94
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