Analogic AAT3218IJS-1.8-T1 150ma micropowerâ ¢ high performance ldo Datasheet

AAT3218
150mA MicroPower™ High Performance LDO
General Description
Features
The AAT3218 MicroPower low dropout linear regulator is ideally suited for portable applications where
very fast transient response, extended battery life,
and small size are critical. The AAT3218 has been
specifically designed for high-speed turn-on and turnoff performance, fast transient response, and good
power supply ripple rejection (PSRR), and is reasonably low noise, making it ideal for powering sensitive
circuits with fast switching requirements.
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Other features include low quiescent current, typically 70µA, and low dropout voltage, typically less than
200mV at the maximum output current level of
150mA. The device is output short-circuit protected
and has a thermal shutdown circuit for additional protection under extreme operating conditions.
The AAT3218 also features a low-power shutdown
mode for extended battery life. A reference bypass
pin has been provided to improve PSRR performance and output noise, by connecting a small
external capacitor from device reference output to
ground.
The AAT3218 is available in a Pb-free, space-saving 5-pin SOT23 or 8-pin SC70JW package in 16
factory-programmed voltages: 1.2V, 1.4V, 1.5V,
1.8V, 1.9V, 2.0V, 2.3V, 2.5V, 2.6V, 2.7V, 2.8V,
2.85V, 2.9V, 3.0V, 3.3V, or 3.5V.
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PowerLinear™
Low Dropout: 200mV at 150mA
Guaranteed 150mA Output
High Accuracy: ±1.5%
70µA Quiescent Current
Fast Line and Load Transient Response
High-Speed Device Turn-On and Shutdown
High Power Supply Ripple Rejection
Low Self Noise
Short-Circuit and Over-Temperature
Protection
Uses Low Equivalent Series Resistance
(ESR) Ceramic Capacitors
Output Noise Reduction Bypass Capacitor
Shutdown Mode for Longer Battery Life
Low Temperature Coefficient
16 Factory-Programmed Output Voltages
SOT23 5-Pin or SC70JW 8-Pin Package
Applications
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Bluetooth™ Headsets
Cellular Phones
Digital Cameras
Notebook Computers
Personal Portable Electronics
Portable Communication Devices
Typical Application
VOUT
VIN
IN
OUT
AAT3218
ON/OFF
BYP
EN
GND
1μF
GND
3218.2006.04.1.8
10nF
2.2μF
GND
1
AAT3218
150mA MicroPower™ High Performance LDO
Pin Descriptions
Pin #
Symbol
Function
SOT23-5
SC70JW-8
1
5, 6
IN
2
8
GND
3
7
EN
Enable pin; this pin should not be left floating. When pulled low,
the PMOS pass transistor turns off and all internal circuitry
enters low-power mode, consuming less than 1µA.
4
1
BYP
Bypass capacitor connection; to improve AC ripple rejection,
connect a 10nF capacitor to GND. This will also provide a softstart function.
5
2, 3, 4
OUT
Output pin; should be decoupled with 2.2µF ceramic capacitor.
Input voltage pin; should be decoupled with 1µF or greater
capacitor.
Ground connection pin.
Pin Configuration
SOT23-5
(Top View)
IN
2
1
GND
2
EN
3
SC70JW-8
(Top View)
5
4
OUT
BYP
BYP
OUT
OUT
OUT
1
8
2
7
3
6
4
5
GND
EN
IN
IN
3218.2006.04.1.8
AAT3218
150mA MicroPower™ High Performance LDO
Absolute Maximum Ratings1
TA = 25°C, unless otherwise noted.
Symbol
Description
VIN
VENIN(MAX)
IOUT
TJ
Input Voltage
Maximum EN to Input Voltage
DC Output Current
Operating Junction Temperature Range
Value
Units
6
0.3
PD/(VIN-VO)
-40 to 150
V
V
mA
°C
Rating
Units
190
526
°C/W
mW
Thermal Information2
Symbol
ΘJA
PD
Description
Maximum Thermal Resistance (SOT23-5, SC70JW-8)
Maximum Power Dissipation (SOT23-5, SC70JW-8)
Recommended Operating Conditions
Symbol
VIN
T
Description
Input Voltage3
Ambient Temperature Range
Rating
Units
(VOUT+VDO) to 5.5
-40 to +85
V
°C
1. 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.
2. Mounted on a demo board.
3. To calculate minimum input voltage, use the following equation: VIN(MIN) = VOUT(MAX) + VDO(MAX) as long as VIN ≥ 2.5V.
3218.2006.04.1.8
3
AAT3218
150mA MicroPower™ High Performance LDO
Electrical Characteristics
VIN = VOUT(NOM) + 1V for VOUT options greater than 1.5V. VIN = 2.5 for VOUT ≤1.5V. IOUT = 1mA, COUT = 2.2µF,
CIN = 1µF, TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C.
Symbol
Description
Conditions
Min
-1.5
-2.5
150
IOUT
VDO
ISC
IQ
ISD
ΔVOUT/
VOUT*ΔVIN
Output Current
Dropout Voltage1, 2
Short-Circuit Current
Ground Current
Shutdown Current
IOUT = 1mA
TA = 25°C
to150mA
TA = -40°C to 85°C
VOUT > 1.2V
IOUT = 150mA
VOUT < 0.4V
VIN = 5V, No Load, EN = VIN
VIN = 5V, EN = 0V
Line Regulation
VIN = VOUT + 1 to 5.0V
ΔVOUT(line)
Dynamic Line Regulation
ΔVOUT(load)
tENDLY
VEN(L)
VEN(H)
IEN
Dynamic Load Regulation
Enable Delay Time
Enable Threshold Low
Enable Threshold High
Leakage Current on Enable Pin
VOUT
PSRR
TSD
THYS
eN
TC
Output Voltage Tolerance
Power Supply Rejection Ratio
Over-Temperature Shutdown
Threshold
Over-Temperature Shutdown
Hysteresis
Output Noise
Output Voltage Temperature
Coefficient
Typ
200
600
70
VIN = VOUT + 1V to VOUT + 2V,
IOUT = 150mA, TR/TF = 2µs
IOUT = 1mA to 150mA, TR< 5µs
BYP = Open
Max
Units
1.5
2.5
%
125
1
mA
mV
mA
µA
µA
0.09
%/V
300
2.5
mV
30
15
0.6
1.5
VEN = 5V
IOUT = 10mA,
CBYP = 10nF
1
1 kHz
10kHz
1MHz
Noise Power BW = 300Hz - 50kHz
mV
µs
V
V
µA
67
47
45
dB
145
°C
12
°C
50
µVrms
22
ppm/°C
1. VDO is defined as VIN - VOUT when VOUT is 98% of nominal.
2. For VOUT < 2.3V, VDO = 2.5V - VOUT.
4
3218.2006.04.1.8
AAT3218
150mA MicroPower™ High Performance LDO
Typical Characteristics
Unless otherwise noted, VIN = 5V, TA = 25°C.
Dropout Voltage vs. Temperature
Dropout Characteristics
3.00
IL = 150mA
Output Voltage (V)
Dropout Voltage (mV)
3.20
260
240
220
200
180
160
140
120
100
80
60
40
20
0
IL = 100mA
IL = 50mA
-40 -30 -20 -10 0
IOUT = 0mA
2.80
IOUT = 10mA
2.60
IOUT = 50mA
2.40
IOUT = 100mA
IOUT = 150mA
2.20
2.00
2.70
10 20 30 40 50 60 70 80 90 100 110 120
Temperature (°C)
2.90
3.10
3.20
Ground Current vs. Input Voltage
90.00
Ground Current (μA)
300
250
200
85°C
150
100
25°C
-40°C
50
80.00
70.00
60.00
50.00
IOUT = 150mA
40.00
IOUT = 50mA
IOUT = 0mA
30.00
IOUT = 10mA
20.00
10.00
0
0
25
50
75
100
125
0.00
150
2
2.5
3
Output Current (mA)
3.5
4
4.5
5
Input Voltage (V)
Output Voltage vs. Temperature
Quiescent Current vs. Temperature
1.203
100
90
1.202
80
Output Voltage (V)
Quiescent Current (μA)
3.00
Input Voltage (V)
Dropout Voltage vs. Output Current
Dropout Voltage (mV)
2.80
70
60
50
40
30
20
10
0
-40 -30 -20 -10
0
10 20 30 40 50 60 70 80 90 100 110 120
Temperature (°C)
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1.201
1.200
1.199
1.198
1.197
1.196
-40 -30 -20 -10
0
10 20
30
40
50 60
70 80
90 100
Temperature (°C)
5
AAT3218
150mA MicroPower™ High Performance LDO
Typical Characteristics
Unless otherwise noted, VIN = 5V, TA = 25°C.
Initial Power-Up Response Time
Turn-Off Response Time
(CBYP = 10nF)
(CBYP = 10nF)
VEN (5V/div)
VEN (5V/div)
VOUT (1V/div)
VOUT (1V/div)
Time (400µs/div)
Time (50µs/div)
Over-Current Protection
Turn-On Time From Enable (VIN present)
(CBYP = 10nF)
1200
Output Current (mA)
VEN (5V/div)
VOUT (1V/div)
1000
800
600
400
200
0
-200
Time (20ms/div)
Time (5µs/div)
Load Transient Response
Line Transient Response
2.85
4
3.02
3
3.01
2
3.00
VOUT
2.99
Output Voltage (V)
3.03
VIN
1
500
VOUT
400
2.80
300
2.75
200
2.70
100
2.65
0
IOUT
0
2.98
Time (100µs/div)
6
2.90
Output Current (mA)
5
3.04
Output Voltage (V)
Input Voltage (V)
6
2.60
-100
Time (100µs/div)
3218.2006.04.1.8
AAT3218
150mA MicroPower™ High Performance LDO
Typical Characteristics
Unless otherwise noted, VIN = 5V, TA = 25°C.
VIH and V IL vs. VIN
AAT3218 Self Noise
Noise Amplitude (µV/rtHz)
(COUT = 10μ
μF, ceramic)
10
1.250
1
1.200
0.1
1.150
1.225
VIH
1.175
1.125
0.01
Band Power:
300Hz to 50kHz = 44.6µVrms/rtHz
100Hz to 100kHz = 56.3µVrms/rtHz
0.001
0.01
0.1
1
10
100
Frequency (kHz)
3218.2006.04.1.8
VIL
1.100
1.075
1000
10000
1.050
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Input Voltage (V)
7
AAT3218
150mA MicroPower™ High Performance LDO
Functional Block Diagram
OUT
IN
Active
Feedback
Control
Over-Current
Protection
OverTemperature
Protection
+
Error
Amplifier
-
EN
FastStart
Control
Voltage
Reference
BYP
Functional Description
The AAT3218 is intended for LDO regulator applications where output current load requirements
range from no load to 150mA. The advanced circuit design of the AAT3218 has been specifically
optimized for very fast start-up and shutdown timing. This proprietary CMOS LDO has also been
tailored for superior transient response characteristics. These traits are particularly important for
applications that require fast power supply timing,
such as GSM cellular telephone handsets.
The high-speed turn-on capability of the AAT3218
is enabled through the implementation of a faststart control circuit, which accelerates the powerup behavior of fundamental control and feedback
circuits within the LDO regulator.
Fast turn-off response time is achieved by an
active output pull-down circuit, which is enabled
when the LDO regulator is placed in shutdown
mode. This active fast shutdown circuit has no
adverse effect on normal device operation.
The AAT3218 has very fast transient response
characteristics, which is an important feature for
applications where fast line and load transient
response are required. This rapid transient
8
GND
response behavior is accomplished through the
implementation of an active error amplifier feedback control. This proprietary circuit design is
unique to this MicroPower LDO regulator.
The LDO regulator output has been specifically
optimized to function with low-cost, low-ESR
ceramic capacitors. However, the design will allow
for operation over a wide range of capacitor types.
A bypass pin has been provided to allow the addition of an optional voltage reference bypass
capacitor to reduce output self noise and increase
power supply ripple rejection. Device self noise
and PSRR will be improved by the addition of a
small ceramic capacitor to this pin. However,
increased CBYPASS values may slow down the LDO
regulator turn-on time.
This LDO regulator has complete short-circuit and
thermal protection. The integral combination of
these two internal protection circuits gives the
AAT3218 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 of this
datasheet for details on device operation at maximum output current loads.
3218.2006.04.1.8
AAT3218
150mA MicroPower™ High Performance LDO
Applications Information
To assure the maximum possible performance is
obtained from the AAT3218, please refer to the following application recommendations.
Input Capacitor
Typically, a 1µF or larger capacitor is recommended for CIN in most applications. A CIN capacitor is
not required for basic LDO regulator operation.
However, if the AAT3218 is physically located more
than three centimeters from an input power source,
a CIN capacitor will be needed for stable operation.
CIN should be located as close to the device VIN pin
as practically possible. CIN values greater than
1µF will offer superior input line transient response
and will assist in maximizing the highest possible
power supply ripple rejection.
Ceramic, tantalum, or aluminum electrolytic capacitors may be selected for CIN. There is no specific
capacitor ESR requirement for CIN. However, for
150mA LDO regulator output operation, ceramic
capacitors are recommended for CIN due 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 VOUT
and GND. The COUT capacitor connection to
the LDO regulator ground pin should be made as
direct as practically possible for maximum device
performance.
The AAT3218 has been specifically designed to function with very low ESR ceramic capacitors. For best
performance, ceramic capacitors are recommended.
Typical output capacitor values for maximum output
current conditions range from 1µF to 10µF.
Applications utilizing the exceptionally low output
noise and optimum power supply ripple rejection
characteristics of the AAT3218 should use 2.2µF or
greater for COUT. If desired, COUT may be increased
without limit.
3218.2006.04.1.8
In low output current applications where output
load is less than 10mA, the minimum value for
COUT can be as low as 0.47µF.
Bypass Capacitor and Low Noise
Applications
A bypass capacitor pin is provided to enhance the
low noise characteristics of the AAT3218 LDO regulator. The bypass capacitor is not necessary for
operation of the AAT3218. However, for best device
performance, a small ceramic capacitor should be
placed between the bypass pin (BYP) and the device
ground pin (GND). The value of CBYP may range
from 470pF to 10nF. For lowest noise and best possible power supply ripple rejection performance, a
10nF capacitor should be used. To practically realize
the highest power supply ripple rejection and lowest
output noise performance, it is critical that the capacitor connection between the BYP pin and GND pin be
direct and PCB traces should be as short as possible. Refer to the PCB Layout Recommendations
section of this datasheet for examples.
There is a relationship between the bypass capacitor value and the LDO regulator turn-on time and
turn-off time. In applications where fast device
turn-on and turn-off time are desired, the value of
CBYP should be reduced.
In applications where low noise performance and/
or ripple rejection are less of a concern, the bypass
capacitor may be omitted. The fastest device turnon time will be realized when no bypass capacitor
is used.
DC leakage on this pin can affect the LDO regulator output noise and voltage regulation performance. For this reason, the use of a low leakage,
high quality ceramic (NPO or C0G type) or film
capacitor is highly recommended.
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use
with the AAT3218. Ceramic capacitors offer many
advantages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically
9
AAT3218
150mA MicroPower™ High Performance LDO
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 not prone to
incorrect connection damage.
Equivalent Series Resistance: ESR is a very
important characteristic to consider when selecting a
capacitor. ESR is the internal series resistance associated with a capacitor that includes lead resistance,
internal connections, 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 C0G materials. NPO and C0G materials generally have tight tolerance and are very stable over
temperature. Larger capacitor values are usually
composed of X7R, X5R, Z5U, or Y5V dielectric
materials. Large ceramic capacitors (i.e., greater
than 2.2µF) are often available in 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
temperature; this could cause problems for circuit
operation. 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 that are physically large in size will have
a lower ESR when compared to a smaller sized
capacitor of an equivalent material and capacitance
value. These larger devices can improve circuit transient response when compared to an equal value
capacitor in a smaller package size.
Consult capacitor vendor datasheets carefully
when selecting capacitors for LDO regulators.
10
Enable Function
The AAT3218 features an LDO regulator enable/
disable function. This pin (EN) is active high and is
compatible with CMOS logic. To assure the LDO
regulator will switch on, the EN turn-on control level
must be greater than 1.5V. The LDO regulator will
go into the disable shutdown mode when the voltage on the EN pin falls below 0.6V. If the enable
function is not needed in a specific application, it
may be tied to VIN to keep the LDO regulator in a
continuously on state.
When the LDO regulator is in shutdown mode, an
internal 1.5kΩ resistor is connected between VOUT
and GND. This is intended to discharge COUT when
the LDO regulator is disabled. The internal 1.5kΩ
has no adverse effect on device turn-on time.
Short-Circuit Protection
The AAT3218 contains an internal short-circuit protection circuit that will trigger when the output load
current exceeds the internal threshold limit. Under
short-circuit conditions, the output of the LDO regulator will be current limited until the short-circuit
condition is removed from the output or LDO regulator package power dissipation exceeds the
device thermal limit.
Thermal Protection
The AAT3218 has an internal thermal protection circuit which will turn on when the device die temperature exceeds 150°C. The internal thermal protection circuit will actively turn off the LDO regulator
output pass device to prevent the possibility of overtemperature damage. The LDO regulator output
will remain in a shutdown state until the internal die
temperature falls back below the 150°C trip point.
The combination and interaction between the shortcircuit and thermal protection systems allows the
LDO regulator to withstand indefinite short-circuit
conditions without sustaining permanent damage.
3218.2006.04.1.8
AAT3218
150mA MicroPower™ High Performance LDO
No-Load Stability
The AAT3218 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.
The following discussions will assume the LDO regulator is mounted on a printed circuit board utilizing
the minimum recommended footprint, as stated in
the Layout Considerations section of this datasheet.
At any given ambient temperature (TA), the maximum package power dissipation can be determined by the following equation:
Reverse Output-to-Input Voltage
Conditions and Protection
Under normal operating conditions, a parasitic
diode exists between the output and input of the
LDO regulator. The input voltage should always
remain greater than the output load voltage, maintaining a reverse bias on the internal parasitic
diode. Conditions where VOUT might exceed VIN
should be avoided since this would forward bias
the internal parasitic diode and allow excessive
current flow into the VOUT pin, possibly damaging
the LDO regulator.
In applications where there is a possibility of VOUT
exceeding VIN for brief amounts of time during normal operation, the use of a larger value CIN capacitor is highly recommended. A larger value of CIN
with respect to COUT will effect a slower CIN decay
rate during shutdown, thus preventing VOUT from
exceeding VIN. In applications where there is a
greater danger of VOUT exceeding VIN for extended
periods of time, it is recommended to place a
Schottky diode across VIN to VOUT (connecting the
cathode to VIN and anode to VOUT). The Schottky
diode forward voltage should be less than 0.45V.
Thermal Considerations and High
Output Current Applications
The AAT3218 is designed to deliver a continuous
output load current of 150mA under normal operating conditions. The limiting characteristic for the
maximum output load current 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 must be
taken into account.
PD(MAX) =
[TJ(MAX) - TA]
θJA
Constants for the AAT3218 are TJ(MAX), the maximum junction temperature for the device which is
125°C and ΘJA = 190°C/W, the package thermal
resistance. Typically, maximum conditions are calculated at the maximum operating temperature
where TA = 85°C, under normal ambient conditions
TA = 25°C. Given TA = 85°C, the maximum package power dissipation is 211mW. At TA = 25°C, the
maximum package power dissipation is 526mW.
The maximum continuous output current for the
AAT3218 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:
IOUT(MAX) <
PD(MAX)
(VIN - VOUT)
For example, if VIN = 5V, VOUT = 3V, and TA = 25°C,
IOUT(MAX) < 264mA. If the output load current were
to exceed 264mA or if the ambient temperature
were to increase, the internal die temperature
would increase. If the condition remained constant, the LDO regulator thermal protection circuit
would activate.
To determine the maximum input voltage 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.
PD(MAX) = (VIN - VOUT)IOUT + (VIN x IGND)
3218.2006.04.1.8
11
AAT3218
150mA MicroPower™ High Performance LDO
This formula can be solved for VIN to determine the
maximum input voltage.
P
+ (VOUT · IOUT)
VIN(MAX) = D(MAX)
IOUT · IGND
The following is an example for an AAT3218 set for
a 2.5V output:
VOUT
= 2.5V
IOUT
= 150mA
IGND
= 150µA
VIN(MAX) =
526mW + (2.5V × 150mA)
150mA + 150µA
VIN(MAX) = 6.00V
From the discussion above, PD(MAX) was determined to equal 526mW at TA = 25°C.
Thus, the AAT3218 can sustain a constant 2.5V
output at a 150mA load current as long as VIN is
≤ 6.0V at an ambient temperature of 25°C. 6.0V is
the absolute maximum voltage where an AAT3218
would never be operated, thus at 25°C, the device
would not have any thermal concerns or operational VIN(MAX) limits.
This situation can be different at 85°C. The following is an example for an AAT3218 set for a 2.5V
output at 85°C:
VOUT
= 2.5V
IOUT
= 150mA
IGND
= 150µA
VIN(MAX) =
211mW + (2.5V × 150mA)
150mA + 150µA
From the discussion above, PD(MAX) was determined to equal 211mW at TA = 85°C.
Higher input-to-output voltage differentials can be
obtained with the AAT3218, 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 VIN = 4.2V
while VOUT = 2.5V at a 150mA load and TA = 85°C.
VIN is greater than 3.90V, which is the maximum
safe continuous input level for VOUT = 2.5V at
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
(PD(MAX) is assumed to be 211mW):
IGND = 150μA
IOUT
= 150mA
VIN
= 4.2V
VOUT = 2.5V
%DC = 100
PD(MAX)
(VIN - VOUT)IOUT + (VIN × IGND)
%DC = 100
211mW
(4.2V - 2.5V)150mA + (4.2V × 150µA)
%DC = 85.54%
For a 150mA output current and a 2.7V drop across
the AAT3218 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 operating area for duty-cycled operation from ambient
room temperature to the maximum operating level.
VIN(MAX) = 3.90V
12
3218.2006.04.1.8
AAT3218
150mA MicroPower™ High Performance LDO
High Peak Output Current Applications
Device Duty Cycle vs. VDROP
(VOUT = 2.5V @ 25°C)
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, first calculate the power dissipation at the
nominal continuous level, then factor in the additional power dissipation due to the short duration,
high-current peaks.
Voltage Drop (V)
3.5
3
2.5
200mA
2
1.5
1
0.5
Duty Cycle (%)
For example, a 2.5V system using an AAT3218IGV2.5-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 4.2V.
Device Duty Cycle vs. VDROP
First, the current duty cycle in percent must be
calculated:
0
0
10
20
30
40
50
60
70
80
90
100
(VOUT = 2.5V @ 50°C)
% Peak Duty Cycle: X/100 = 378µs/4.61ms
% Peak Duty Cycle = 8.2%
Voltage Drop (V)
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
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.
Duty Cycle (%)
PD(MAX) = (VIN - VOUT)IOUT + (VIN x IGND)
PD(100mA) = (4.2V - 2.5V)100mA + (4.2V x 150µA)
PD(100mA) = 170.6mW
Device Duty Cycle vs. VDROP
(VOUT = 2.5V @ 85°C)
3.5
100mA
Voltage Drop (V)
3
2.5
The power dissipation for a 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:
200mA
2
1.5
150mA
1
PD(91.8%D/C) = %DC x PD(100mA)
PD(91.8%D/C) = 0.918 x 170.6mW
PD(91.8%D/C) = 156.6mW
0.5
0
0
10
20
30
40
50
60
Duty Cycle (%)
70
80
90
100
PD(MAX) = (VIN - VOUT)IOUT + (VIN x IGND)
PD(150mA) = (4.2V - 2.5V)150mA + (4.2V x 150mA)
PD(150mA) = 255.6mW
PD(8.2%D/C) = %DC x PD(150mA)
PD(8.2%D/C) = 0.082 x 255.6mW
PD(8.2%D/C) = 21mW
3218.2006.04.1.8
13
AAT3218
150mA MicroPower™ High Performance LDO
The power dissipation for a 150mA load occurring
for 8.2% of the duty cycle will be 21mW. Finally,
the two power dissipation levels can summed to
determine the total true power dissipation under
the varied load:
(CIN, COUT, and CBYP), and the load circuit are all
connected to a common ground plane. This type of
layout will work in simple applications where good
power supply ripple rejection and low self noise are
not a design concern. For high-performance applications, this method is not recommended.
PD(total) = PD(100mA) + PD(150mA)
PD(total) = 156.6mW + 21mW
PD(total) = 177.6mW
The problem with the layout in Figure 1 is the
bypass capacitor and output capacitor share the
same ground path to the LDO regulator ground pin,
along with the high-current return path from the
load back to the power supply. The bypass capacitor node is connected directly to the LDO regulator
internal reference, making this node very sensitive
to noise or ripple. The internal reference output is
fed into the error amplifier, thus any noise or ripple
from the bypass capacitor will be subsequently
amplified by the gain of the error amplifier. This
effect can increase noise seen on the LDO regulator output, as well as reduce the maximum possible power supply ripple rejection. There is PCB
trace impedance between the bypass capacitor
connection to ground and the LDO regulator
ground connection. When the high load current
returns through this path, a small ripple voltage is
created, feeding into the CBYP loop.
The maximum power dissipation for the AAT3218
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.
Printed Circuit Board Layout
Recommendations
In order to obtain the maximum performance from
the AAT3218 LDO regulator, careful consideration
should be given to the printed circuit board (PCB)
layout. If grounding connections are not properly
made, power supply ripple rejection, low output self
noise, and transient response can be compromised.
Figure 1 shows a common LDO regulator layout
scheme. The LDO regulator, external capacitors
VIN
ILOAD
IIN
VIN
LDO VOUT
Regulator
EN
DC INPUT
BYP
GND
CIN
CBYP
IGND
IRIPPLE
COUT
RLOAD
CBYP
IBYP + noise
GND
LOOP
GND
RTRACE
RTRACE
RTRACE
RTRACE
ILOAD return + noise and ripple
Figure 1: Common LDO Regulator Layout with CBYP Ripple Feedback Loop.
Figure 2 shows the preferred method for the bypass
and output capacitor connections. For low output
noise and highest possible power supply ripple
rejection performance, it is critical to connect the
14
bypass and output capacitor directly to the LDO regulator ground pin. This method will eliminate any
load noise or ripple current feedback through the
LDO regulator.
3218.2006.04.1.8
AAT3218
150mA MicroPower™ High Performance LDO
ILOAD
IIN
VIN
VIN
LDO VOUT
Regulator
BYP
EN
GND
DC INPUT
CIN
IGND
CBYP
COUT
RLOAD
IBYP only
IRIPPLE
GND
RTRACE
RTRACE
RTRACE
RTRACE
ILOAD return + noise and ripple
Figure 2: Recommended LDO Regulator Layout.
Evaluation Board Layout
The AAT3218 evaluation layout follows the recommend printed circuit board layout procedures and
Figure 3: Evaluation Board
Component Side Layout.
3218.2006.04.1.8
can be used as an example for good application
layouts.
Note: Board layout is not shown to scale.
Figure 4: Evaluation Board
Solder Side Layout.
Figure 5: Evaluation Board
Top Side Silk Screen Layout /
Assembly Drawing.
15
AAT3218
150mA MicroPower™ High Performance LDO
Ordering Information
Output Voltage
Package
Marking1
Part Number (Tape and Reel)2
1.2V
1.5V
1.8V
1.9V
2.0V
2.3V
2.5V
2.6V
2.7V
2.8V
2.85V
2.9V
3.0V
3.3V
3.5V
1.2V
1.25V
1.4V
1.5V
1.8V
1.9V
2.0V
2.3V
2.5V
2.6V
2.7V
2.8V
2.85V
2.9V
3.0V
3.3V
3.5V
SOT23-5
SOT23-5
SOT23-5
SOT23-5
SOT23-5
SOT23-5
SOT23-5
SOT23-5
SOT23-5
SOT23-5
SOT23-5
SOT23-5
SOT23-5
SOT23-5
SOT23-5
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
KWXYY
GZXYY
HBXYY
HDXYY
NVXYY
AAT3218IGV-1.2-T1
AAT3218IGV-1.5-T1
AAT3218IGV-1.8-T1
AAT3218IGV-1.9-T1
AAT3218IGV-2.0-T1
AAT3218IGV-2.3-T1
AAT3218IGV-2.5-T1
AAT3218IGV-2.6-T1
AAT3218IGV-2.7-T1
AAT3218IGV-2.8-T1
AAT3218IGV-2.85-T1
AAT3218IGV-2.9-T1
AAT3218IGV-3.0-T1
AAT3218IGV-3.3-T1
AAT3218IGV-3.5-T1
AAT3218IJS-1.2-T1
AAT3218IJS-1.25-T1
AAT3218IJS-1.4-T1
AAT3218IJS-1.5-T1
AAT3218IJS-1.8-T1
AAT3218IJS-1.9-T1
AAT3218IJS-2.0-T1
AAT3218IJS-2.3-T1
AAT3218IJS-2.5-T1
AAT3218IJS-2.6-T1
AAT3218IJS-2.7-T1
AAT3218IJS-2.8-T1
AAT3218IJS-2.85-T1
AAT3218IJS-2.9-T1
AAT3218IJS-3.0-T1
AAT3218IJS-3.3-T1
AAT3218IJS-3.5-T1
HNXYY
GWXYY
EOXYY
EMXYY
HOXYY
GXXYY
HPXYY
IUXYY
KWXYY
LWXYY
JUXYY
GZXYY
HBXYY
HDXYY
NVXYY
HNXYY
GWXYY
EOXYY
EMXYY
HOXYY
GXXYY
HPXYY
IUXYY
All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means
semiconductor products that are in compliance with current RoHS standards, including
the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more
information, please visit our website at http://www.analogictech.com/pbfree.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
16
3218.2006.04.1.8
AAT3218
150mA MicroPower™ High Performance LDO
Package Information
SOT23-5
2.85 ± 0.15
1.90 BSC
0.40 ± 0.10
0.075 ± 0.075
0.15 ± 0.07
4° ± 4°
10° ± 5°
1.10 ± 0.20
0.60 REF
1.20 ± 0.25
2.80 ± 0.20
1.575 ± 0.125
0.95
BSC
0.60 REF
0.45 ± 0.15
GAUGE PLANE
0.10 BSC
All dimensions in millimeters.
3218.2006.04.1.8
17
AAT3218
150mA MicroPower™ High Performance LDO
SC70JW-8
2.20 ± 0.20
1.75 ± 0.10
0.50 BSC 0.50 BSC 0.50 BSC
0.225 ± 0.075
2.00 ± 0.20
0.100
7° ± 3°
0.45 ± 0.10
4° ± 4°
0.05 ± 0.05
0.15 ± 0.05
1.10 MAX
0.85 ± 0.15
0.048REF
2.10 ± 0.30
All dimensions in millimeters.
© Advanced Analogic Technologies, Inc.
AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights,
or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice.
Customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech
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Phone (408) 737-4600
Fax (408) 737-4611
18
3218.2006.04.1.8
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