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150mA MicroPowerTM High Performance LDO General Description
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. Other features include low quiescent current, typically 70A, 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.
AAT3218
Features
* * * * * * * * * * * * * * *
PowerLinearTM
Low Dropout: 200mV at 150mA Guaranteed 150mA Output High Accuracy: 1.5% 70A 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
* * * * * * BluetoothTM Headsets Cellular Phones Digital Cameras Notebook Computers Personal Portable Electronics Portable Communication Devices
Typical Application
VIN IN OUT VOUT
AAT3218
ON/OFF 1F EN GND 10nF 2.2F BYP
GND
GND
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150mA MicroPowerTM High Performance LDO Pin Descriptions
Pin #
SOT23-5 SC70JW-8
AAT3218
Symbol
IN GND EN
Function
Input voltage pin; should be decoupled with 1F or greater capacitor. Ground connection pin. 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 1A. Bypass capacitor connection; to improve AC ripple rejection, connect a 10nF capacitor to GND. This will also provide a softstart function. Output pin; should be decoupled with 2.2F ceramic capacitor.
1 2 3
5, 6 8 7
4
1
BYP
5
2, 3, 4
OUT
Pin Configuration
SOT23-5 (Top View) SC70JW-8 (Top View)
IN GND EN
1
5
OUT
2
3
4
BYP
BYP OUT OUT OUT
1 2 3 4
8 7 6 5
GND EN IN IN
2
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150mA MicroPowerTM High Performance LDO Absolute Maximum Ratings1
TA = 25C, unless otherwise noted. Symbol
VIN VENIN(MAX) IOUT TJ
AAT3218
Description
Input Voltage Maximum EN to Input Voltage DC Output Current Operating Junction Temperature Range
Value
6 0.3 PD/(VIN-VO) -40 to 150
Units
V V mA C
Thermal Information2
Symbol
JA PD
Description
Maximum Thermal Resistance (SOT23-5, SC70JW-8) Maximum Power Dissipation (SOT23-5, SC70JW-8)
Rating
190 526
Units
C/W mW
Recommended Operating Conditions
Symbol
VIN T
Description
Input Voltage3 Ambient Temperature Range
Rating
(VOUT+VDO) to 5.5 -40 to +85
Units
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
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150mA MicroPowerTM High Performance LDO Electrical Characteristics
AAT3218
VIN = VOUT(NOM) + 1V for VOUT options greater than 1.5V. VIN = 2.5 for VOUT 1.5V. IOUT = 1mA, COUT = 2.2F, CIN = 1F, TA = -40C to +85C, unless otherwise noted. Typical values are TA = 25C. Symbol
VOUT IOUT VDO ISC IQ ISD VOUT/ VOUT*VIN VOUT(line) VOUT(load) tENDLY VEN(L) VEN(H) IEN PSRR TSD THYS eN TC
Description
Output Voltage Tolerance Output Current Dropout Voltage1, 2 Short-Circuit Current Ground Current Shutdown Current Line Regulation Dynamic Line Regulation Dynamic Load Regulation Enable Delay Time Enable Threshold Low Enable Threshold High Leakage Current on Enable Pin Power Supply Rejection Ratio Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Output Noise Output Voltage Temperature Coefficient
Conditions
IOUT = 1mA TA = 25C to150mA TA = -40C to 85C VOUT > 1.2V IOUT = 150mA VOUT < 0.4V VIN = 5V, No Load, EN = VIN VIN = 5V, EN = 0V VIN = VOUT + 1 to 5.0V VIN = VOUT + 1V to VOUT + 2V, IOUT = 150mA, TR/TF = 2s IOUT = 1mA to 150mA, TR< 5s BYP = Open
Min
-1.5 -2.5 150
Typ
Max
1.5 2.5
Units
% mA mV mA A A %/V mV mV s V V A dB C C Vrms ppm/C
200 600 70
300 125 1 0.09
2.5 30 15 0.6 1.5
VEN = 5V IOUT = 10mA, CBYP = 10nF 1 kHz 10kHz 1MHz 67 47 45 145 12 Noise Power BW = 300Hz - 50kHz 50 22
1
1. VDO is defined as VIN - VOUT when VOUT is 98% of nominal. 2. For VOUT < 2.3V, VDO = 2.5V - VOUT.
4
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150mA MicroPowerTM High Performance LDO Typical Characteristics
Unless otherwise noted, VIN = 5V, TA = 25C.
AAT3218
Dropout Voltage vs. Temperature
3.20
260 240 220 200 180 160 140 120 100 80 60 40 20 0
Dropout Characteristics
Dropout Voltage (mV)
Output Voltage (V)
IL = 150mA IL = 100mA
3.00 2.80 2.60 2.40 2.20 2.00 2.70
IOUT = 0mA IOUT = 10mA IOUT = 50mA IOUT = 100mA IOUT = 150mA
IL = 50mA
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120
Temperature (C)
2.80
2.90
3.00
3.10
3.20
Input Voltage (V)
Dropout Voltage vs. Output Current
300
90.00 80.00 70.00 60.00 50.00 40.00 30.00 20.00 10.00
Ground Current vs. Input Voltage
Dropout Voltage (mV)
250 200 150 100 50 0 0 25 50 75 100 125 150
85C 25C -40C
Ground Current (A)
IOUT = 150mA IOUT = 0mA IOUT = 50mA
IOUT = 10mA
0.00 2 2.5 3 3.5 4 4.5 5
Output Current (mA)
Input Voltage (V)
Quiescent Current vs. Temperature
100
Output Voltage vs. Temperature
1.203 1.202
Quiescent Current (A)
90
Output Voltage (V)
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120
80 70 60 50 40 30 20 10 0
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)
Temperature (C)
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150mA MicroPowerTM High Performance LDO Typical Characteristics
Unless otherwise noted, VIN = 5V, TA = 25C.
AAT3218
Initial Power-Up Response Time
(CBYP = 10nF)
Turn-Off Response Time
(CBYP = 10nF)
VEN (5V/div)
VEN (5V/div)
VOUT (1V/div) Time (400s/div)
VOUT (1V/div) Time (50s/div)
Turn-On Time From Enable (VIN present)
(CBYP = 10nF)
1200
Over-Current Protection
VEN (5V/div)
Output Current (mA)
VOUT (1V/div) Time (5s/div)
1000 800 600 400 200 0 -200
Time (20ms/div)
Line Transient Response
6 5 3.04 3.03
2.90 2.85 2.80 2.75 2.70 2.65
Load Transient Response
500
VIN
4 3 2 1 0 3.02 3.01 3.00
Output Voltage (V)
Input Voltage (V)
VOUT
400 300 200 100 0
Output Current (mA)
Output Voltage (V)
VOUT
2.99 2.98
IOUT
2.60 -100
Time (100s/div)
Time (100s/div)
6
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150mA MicroPowerTM High Performance LDO Typical Characteristics
Unless otherwise noted, VIN = 5V, TA = 25C.
AAT3218
AAT3218 Self Noise
(COUT = 10F, ceramic)
VIH and V IL vs. VIN
1.250 1.225
Noise Amplitude (V/rtHz)
10
1
1.200 1.175
VIH
0.1 Band Power: 300Hz to 50kHz = 44.6Vrms/rtHz 100Hz to 100kHz = 56.3Vrms/rtHz
1.150 1.125
0.01
1.100 1.075 100 1000 10000 1.050 2.5 3.0 3.5
VIL
0.001 0.01 0.1 1 10
4.0
4.5
5.0
5.5
Frequency (kHz)
Input Voltage (V)
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150mA MicroPowerTM High Performance LDO Functional Block Diagram
AAT3218
IN
Active Feedback Control Over-Current Protection
OUT
OverTemperature Protection + Error Amplifier -
EN
FastStart Control
Voltage Reference
BYP
GND
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
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.
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150mA MicroPowerTM High Performance LDO Applications Information
To assure the maximum possible performance is obtained from the AAT3218, please refer to the following application recommendations.
AAT3218
In low output current applications where output load is less than 10mA, the minimum value for COUT can be as low as 0.47F.
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.
Input Capacitor
Typically, a 1F 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 1F 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 1F to 10F. Applications utilizing the exceptionally low output noise and optimum power supply ripple rejection characteristics of the AAT3218 should use 2.2F or greater for COUT. If desired, COUT may be increased without limit.
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
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150mA MicroPowerTM 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 0.1F 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 2.2F) 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 2.2F Y5V capacitor could be reduced to 1F 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.
AAT3218
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 1.5k resistor is connected between VOUT and GND. This is intended to discharge COUT when the LDO regulator is disabled. The internal 1.5k 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 150C. 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 150C 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.
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150mA MicroPowerTM 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.
AAT3218
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.
PD(MAX) =
[TJ(MAX) - TA] JA
Constants for the AAT3218 are TJ(MAX), the maximum junction temperature for the device which is 125C and JA = 190C/W, the package thermal resistance. Typically, maximum conditions are calculated at the maximum operating temperature where TA = 85C, under normal ambient conditions TA = 25C. Given TA = 85C, the maximum package power dissipation is 211mW. At TA = 25C, 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)
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.
For example, if VIN = 5V, VOUT = 3V, and TA = 25C, 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)
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150mA MicroPowerTM High Performance LDO
This formula can be solved for VIN to determine the maximum input voltage.
AAT3218
From the discussion above, PD(MAX) was determined to equal 211mW at TA = 85C. 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 = 85C. VIN is greater than 3.90V, which is the maximum safe continuous input level for VOUT = 2.5V at 150mA for TA = 85C. 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 = 150A IOUT VIN = 150mA = 4.2V
P + (VOUT * IOUT) VIN(MAX) = D(MAX) IOUT * IGND
The following is an example for an AAT3218 set for a 2.5V output:
VOUT IOUT IGND
= 2.5V = 150mA = 150A 526mW + (2.5V x 150mA) 150mA + 150A
VIN(MAX) =
VIN(MAX) = 6.00V
From the discussion above, PD(MAX) was determined to equal 526mW at TA = 25C. 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 25C. 6.0V is the absolute maximum voltage where an AAT3218 would never be operated, thus at 25C, the device would not have any thermal concerns or operational VIN(MAX) limits. This situation can be different at 85C. The following is an example for an AAT3218 set for a 2.5V output at 85C:
VOUT IOUT IGND = 2.5V = 150mA = 150A 211mW + (2.5V x 150mA) 150mA + 150A
VOUT = 2.5V %DC = 100 %DC = 100 PD(MAX) (VIN - VOUT)IOUT + (VIN x IGND) 211mW (4.2V - 2.5V)150mA + (4.2V x 150A)
%DC = 85.54%
For a 150mA output current and a 2.7V drop across the AAT3218 at an ambient temperature of 85C, 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) =
VIN(MAX) = 3.90V
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150mA MicroPowerTM High Performance LDO
Device Duty Cycle vs. VDROP
(VOUT = 2.5V @ 25C)
3.5
AAT3218
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, 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.
90 100
Voltage Drop (V)
3 2.5 2 1.5 1 0.5 0 0 10 20 30 40 50 60 70 80
200mA
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 378s out of a 4.61ms period. 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 = 378s/4.61ms % Peak Duty Cycle = 8.2%
Device Duty Cycle vs. VDROP
(VOUT = 2.5V @ 50C)
3.5
Voltage Drop (V)
3 2.5 2 1.5 1 0.5 0 0 10 20 30 40 50 60 70 80 90 100
200mA 150mA
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. PD(MAX) = (VIN - VOUT)IOUT + (VIN x IGND) PD(100mA) = (4.2V - 2.5V)100mA + (4.2V x 150A) PD(100mA) = 170.6mW 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 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:
Duty Cycle (%)
Device Duty Cycle vs. VDROP
(VOUT = 2.5V @ 85C)
3.5 3
100mA
Voltage Drop (V)
2.5 2 1.5 1 0.5 0 0 10 20 30 40 50 60 70 80 90 100
200mA 150mA
Duty Cycle (%)
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
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150mA MicroPowerTM 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: PD(total) = PD(100mA) + PD(150mA) PD(total) = 156.6mW + 21mW PD(total) = 177.6mW The maximum power dissipation for the AAT3218 operating at an ambient temperature of 85C 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. (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. 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.
AAT3218
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
IIN
ILOAD VIN EN
LDO VOUT Regulator
BYP GND IGND
DC INPUT
CIN
CBYP
IBYP + noise CBYP
GND LOOP
COUT
RLOAD
IRIPPLE
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
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.
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150mA MicroPowerTM High Performance LDO
ILOAD VIN EN GND
AAT3218
IIN
VIN
LDO VOUT Regulator
BYP
DC INPUT
CIN
IRIPPLE
IGND
CBYP
IBYP only
COUT
RLOAD
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
can be used as an example for good application layouts. Note: Board layout is not shown to scale.
Figure 3: Evaluation Board Component Side Layout.
Figure 4: Evaluation Board Solder Side Layout.
Figure 5: Evaluation Board Top Side Silk Screen Layout / Assembly Drawing.
3218.2006.04.1.8
15
150mA MicroPowerTM High Performance LDO Ordering Information
Output Voltage
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
AAT3218
Package
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
Marking1
KWXYY GZXYY HBXYY HDXYY NVXYY HNXYY GWXYY EOXYY EMXYY HOXYY GXXYY HPXYY IUXYY KWXYY LWXYY JUXYY GZXYY HBXYY HDXYY NVXYY HNXYY GWXYY EOXYY EMXYY HOXYY GXXYY HPXYY IUXYY
Part Number (Tape and Reel)2
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
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
150mA MicroPowerTM High Performance LDO Package Information
SOT23-5
2.85 0.15 1.90 BSC 0.95 BSC
AAT3218
1.575 0.125
1.10 0.20
0.60 REF
2.80 0.20
1.20 0.25
0.15 0.07
4 4
GAUGE PLANE
10 5
0.40 0.10
0.075 0.075
0.60 REF
0.45 0.15
0.10 BSC
All dimensions in millimeters.
3218.2006.04.1.8
17
150mA MicroPowerTM High Performance LDO
SC70JW-8
0.50 BSC 0.50 BSC 0.50 BSC
AAT3218
1.75 0.10
0.225 0.075 2.00 0.20
2.20 0.20
0.048REF
0.85 0.15
1.10 MAX
0.15 0.05
0.100
7 3
0.45 0.10 2.10 0.30
4 4
All dimensions in millimeters.
(c) 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 warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech's standard warranty. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 18
3218.2006.04.1.8
0.05 0.05

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