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 turn off performance, fast transient response, 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 70µA, and low dropout voltage which is 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 the AAT3218's reference output to ground. The AAT3218 is available in a space saving 5-pin SOT23 or 8-pin SC70JW package in 16 factory programmed voltages of 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. 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 protection Over-Temperature protection Uses Low 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 • • • • • Cellular Phones Notebook Computers Portable Communication Devices Personal Portable Electronics Digital Cameras Typical Application VIN VOUT IN OUT AAT3218 ON/OFF BYP EN GND 1µF GND 3218.2004.02.1.0 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 4 1 BYP Bypass capacitor connection - to improve AC ripple rejection, connect a 10nF capacitor to GND. This will also provide a soft start 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 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. Pin Configuration SOT23-5 (Top View) OUT BYP BYP OUT OUT OUT 1 8 7 2 2 2 1 5 2 3 4 1 IN GND EN SC70JW-8 (Top View) 3 6 4 5 GND EN IN IN 3218.2004.02.1.0 AAT3218 150mA MicroPower™ High Performance LDO Absolute Maximum Ratings Symbol VIN IOUT TJ (TA=25°C unless otherwise noted) Description Input Voltage DC Output Current Operating Junction Temperature Range Value Units 6 PD/(VIN-VO) -40 to 150 V mA °C 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. Thermal Information Symbol ΘJA PD Description Maximum Thermal Resistance (SOT23-5, SC70JW-8) Maximum Power Dissipation1 (SOT23-5, SC70JW-8) 1 Rating Units 190 526 °C/W mW Note 1: Mounted on a demo board. Recommended Operating Conditions Symbol VIN T Description Input Voltage Ambient Temperature Range 2 Rating Units (VOUT+VDO) to 5.5 -40 to +85 V °C Note 2: To calculate minimum input voltage, use the following equation: VIN(MIN) = VOUT(MAX) + VDO(MAX) as long as VIN ≥ 2.5V. 3218.2004.02.1.0 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 to 85°C unless otherwise noted. Typical values are at TA=25°C) Symbol VOUT Description Conditions Min Typ Max Output Voltage Tolerance IOUT = 1mA to 150mA Output Current Dropout Voltage 1, 2 Short Circuit Current Ground Current Shutdown Current VOUT > 1.2V IOUT = 150mA VOUT < 0.4V VIN = 5V, No load, EN = VIN VIN = 5V, EN = 0V TA=25°C -1.5 TA=-40 to 85°C -2.5 150 IOUT VDO ISC IQ ISD ∆VOUT/ VOUT*∆VIN ∆VOUT(line) Line Regulation VIN = VOUT + 1 to 5.0V Dynamic Line Regulation ∆VOUT(load) tENDLY VEN(L) VEN(H) IEN Dynamic Load Regulation Enable Delay Time Enable Threshold Low Enable Threshold High Leakage Current on Enable Pin VIN=VOUT+1V to VOUT+2V, IOUT=150mA, TR/TF =2µs IOUT = 1mA to 150mA, TR<5µs BYP = open PSRR TSD THYS eN TC Power Supply Rejection Ratio 1.5 2.5 200 600 70 125 1 % % mA mV mA µA µA 0.09 %/V 300 2.5 mV 30 15 mV µs V V µA 0.6 1.5 VEN = 5V 1 kHz IOUT=10mA, CBYP=10nF 10kHz 1MHz Over Temp Shutdown Threshold Over Temp Shutdown Hysteresis Output Noise Noise Power BW = 300Hz-50kHz Output Voltage Temp. Coeff. Units 1 67 47 45 145 12 50 22 dB °C °C µVrms/rtHz ppm/°C Note 1: VDO is defined as VIN - VOUT when VOUT is 98% of nominal. Note 2: For VOUT < 2.3V, VDO = 2.5V - VOUT. 4 3218.2004.02.1.0 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 IOUT = 0mA 2.80 V OUT (V) Dropout Voltage (mV) 3.20 260 240 220 200 180 160 140 120 100 80 60 40 20 0 IL = 100mA IOUT = 10mA 2.60 IOUT = 50mA 2.40 IL = 50mA -40 -30 -20 -10 0 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 3.00 3.20 Ground Current vs. Input Voltage 90.00 300 80.00 250 70.00 IGND (µA) 200 85°C 150 100 50.00 IOUT=150mA 40.00 IOUT=50mA IOUT=0mA IOUT=10mA 20.00 -40°C 50 60.00 30.00 25°C 10.00 0 0 25 50 75 100 125 0.00 150 2 2.5 3 3.5 Output Current (mA) 4 4.5 VIN (V) Output Voltage vs. Temperature Quiescent Current vs. Temperature 1.203 100 90 1.202 80 Output Voltage (V) Quiescent Current (µA) 3.10 VIN (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) 3218.2004.02.1.0 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) 5 AAT3218 150mA MicroPower™ High Performance LDO Typical Characteristics (Unless otherwise noted, VIN = 5V, TA = 25°C) Initial Power Up Response Time CBYP=10nF Turn-OFF Response Time CBYP=10nF VEN (5V/div) VEN (5V/div) VOUT (1V/div) VOUT (1V/div) 50 µs/div 400µs/div Over Current Protection Turn-ON Time From Enable (VIN present) CBYP=10nF 1200 1000 VEN (5V/div) IOUT (mA) 800 600 400 200 0 -200 VOUT (1V/div) Time (20 ms/div) 5 µs/div Load Transient Response Line Transient Response 500 2.90 6 3.04 5 3.03 V IN (V) 3 3.01 2 3.00 V OUT (V) 3.02 VOUT 400 2.80 300 2.75 200 2.70 100 2.65 1 VOUT 2.99 0 2.98 I OUT (mA) VIN 4 VOUT (V) 2.85 0 IOUT 2.60 -100 100µs/div 100µs/div 6 3218.2004.02.1.0 AAT3218 150mA MicroPower™ High Performance LDO Typical Characteristics (Unless otherwise noted, VIN = 5V, TA = 25°C) AAT3218 Self Noise COUT = 10µF (ceramic) VIH and V IL vs. VIN Noise Amplitude (µV/rtHz) 1.250 1.225 10 1.200 1 VIH 1.175 1.150 0.1 0.01 1.125 0.001 0.01 0.1 1 10 1.075 100 Frequency (kHz) 3218.2004.02.1.0 VIL 1.100 Band Power: 300Hz to 50kHz = 44.6µVrms/rtHz 100Hz to 100kHz = 56.3µVrms/rtHz 1000 10000 1.050 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VIN (V) 7 AAT3218 150mA MicroPower™ High Performance LDO Functional Block Diagram OUT IN Active Feedback Control Over-Current Protection OverTemperature Protection + Error Amplifier - EN Fast Start 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, which 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 fast start control circuit, which accelerates the power up behavior of fundamental control and feedback circuits within the LDO regulator. Fast turn-off time response is achieved by an active output pull down circuit, which is enabled when the LDO regulator is placed in the 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 is 8 GND required. This rapid transient 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 in this pin. However, increased values of CBYPASS 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 give 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 discussion in the section for details on device operation at maximum output current loads. 3218.2004.02.1.0 AAT3218 150mA MicroPower™ High Performance LDO Applications Information Bypass Capacitor and Low Noise Applications To assure the maximum possible performance is obtained from the AAT3218, please refer to the following application recommendations. 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 document for examples. 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 3 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. In low output current applications where output load is less then 10mA, the minimum value for COUT can be as low as 0.47µF. 3218.2004.02.1.0 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 time and turn off time is 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 turn on 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 COG 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 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. 9 AAT3218 150mA MicroPower™ High Performance LDO Applications Information 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, 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 very stable over temperature. Larger capacitor values are typically composed of X7R, X5R, Z5U and Y5V dielectric materials. Large ceramic capacitors, typically greater then 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 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 which 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 data sheets carefully when selecting capacitors for LDO regulators. 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 1.5 volts. The LDO regulator will go into the disable shutdown mode when the voltage on the EN pin falls below 0.6 volts. 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. 10 When the LDO regulator is in the 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 over temperature 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 short circuit and thermal protection systems allow the LDO regulator to withstand indefinite short circuit conditions without sustaining permanent damage. 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. 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 then 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. 3218.2004.02.1.0 AAT3218 150mA MicroPower™ High Performance LDO Applications Information 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 0.45 volts. 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 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 as stated in the layout considerations section of the document. pation 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°, IOUT(MAX) < 264mA. If the output load current were to exceed 264mA or if the ambient temperature were to increase, the internal die temperature will increase. If the condition remained constant, the LDO regulator thermal protection circuit will activate. 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. PD(MAX) = (VIN - VOUT)IOUT + (VIN x IGND) This formula can be solved for VIN to determine the maximum input voltage. VIN(MAX) = (PD(MAX) + (VOUT x IOUT)) / (IOUT + IGND) The following is an example for an AAT3218 set for a 2.5 volt output: From the discussion above, PD(MAX) was determined to equal 526mW at TA = 25°C. VOUT = 2.5 volts IOUT = 150mA IGND = 150µA At any given ambient temperature (TA) the maximum package power dissipation can be determined by the following equation: VIN(MAX)=(526mW+(2.5Vx150mA))/(150mA +150µA) PD(MAX) = [TJ(MAX) - TA] / ΘJA Thus, the AAT3218 can sustain a constant 2.5V output at a 150mA load current as long as VIN is ≤ 6.00V 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. 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°, 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 dissi- 3218.2004.02.1.0 VIN(MAX) = 6.00V This situation can be different at 85°C. The following is an example for an AAT3218 set for a 2.5 volt output at 85°C: From the discussion above, PD(MAX) was determined to equal 211mW at TA = 85°C. 11 AAT3218 150mA MicroPower™ High Performance LDO Applications Information VIN(MAX) = 3.90V 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 = 4.2 volts Voltage Drop (V) VIN(MAX)=(211mW+(2.5Vx150mA))/(150mA +150uA) 3.5 3 2.5 200mA 2 1.5 1 0.5 0 0 10 20 30 40 50 60 70 80 90 100 Duty Cycle (%) Device Duty Cycle vs. VDROP VOUT= 2.5V @ 50 C 3.5 Voltage Drop (V) VOUT = 2.5 volts IOUT = 150mA IGND = 150uA Device Duty Cycle vs. V DROP VOUT = 2.5V @ 25 C 3 2.5 200mA 2 150mA 1.5 1 0.5 0 0 10 20 30 40 50 60 70 80 90 100 Duty Cycle (%) VOUT = 2.5 volt %DC=100(PD(MAX)/((VIN-VOUT)IOUT+(VINxIGND)) %DC=100(211mW/((4.2V-2.5V)150mA+(4.2Vx150µA)) Device Duty Cycle vs. VDROP VOUT = 2.5V @ 85 C %DC = 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. 3.5 Voltage Drop (V) For a 150mA output current and a 2.7volt drop across the AAT3218 at an ambient temperature of 85°C, the maximum on time duty cycle for the device would be 85.54%. 100mA 3 2.5 200mA 2 1.5 150mA 1 0.5 0 0 10 20 30 40 50 60 70 80 90 100 Duty Cycle (%) 12 3218.2004.02.1.0 AAT3218 150mA MicroPower™ High Performance LDO Applications Information High Peak Output Current Applications two power dissipation levels can summed to determine the total true power dissipation under the varied load. Some applications require the LDO regulator to operate at continuous nominal level with short duration high current peaks. The duty cycles for both output current levels must be taken into account. To do so, one would first need to calculate the power dissipation at the nominal continuous level, then factor in the additional power dissipation due to the short duration high current peaks. PD(total) = PD(100mA) + PD(150mA) PD(total) = 156.6mW + 21mW PD(total) = 177.6mW For example, a 2.5V system using a 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. Printed Circuit Board Layout Recommendations First the current duty cycle in percent must be calculated: % Peak Duty Cycle: X/100 = 378µs/4.61ms % Peak Duty Cycle = 8.2% The LDO Regulator will be under the 100mA load for 91.8% of the 4.61ms period and have 150mA peaks occurring for 8.2% of the time. Next, the continuous nominal power dissipation for the 100mA load should be determined then multiplied by the duty cycle to conclude the actual power dissipation over time. PD(MAX) = (VIN - VOUT)IOUT + (VIN x IGND) PD(100mA) = (4.2V - 2.5V)100mA + (4.2V x 150µA) 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 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: 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 The power dissipation for 150mA load occurring for 8.2% of the duty cycle will be 21mW. Finally, the 3218.2004.02.1.0 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. In order to obtain the maximum performance from the AAT3218 LDO regulator, very careful attention must be considered in regard 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 (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. 13 AAT3218 150mA MicroPower™ High Performance LDO Applications Information ILOAD IIN VIN VIN EN DC INPUT LDO Regulator VOUT BYP GND CIN GND CBYP IGND IRIPPLE IBYP + noise RTRACE COUT CBYP RLOAD GND LOOP 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. ILOAD IIN VIN VIN EN LDO Regulator VOUT BYP 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 14 can be used as an example for good application layouts. Note: Board layout shown is not to scale. Figure 4: Evaluation board solder side layout Figure 5: Evaluation board top side silk screen layout / assembly drawing 3218.2004.02.1.0 AAT3218 150mA MicroPower™ 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 1.4V 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 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 Marking1 GZXYY HBXYY HDXYY HNXYY GWXYY EOXYY EMXYY HOXYY GXXYY HPXYY KWXYY JUXYY GZXYY HBXYY HDXYY HNXYY GWXYY EOXYY EMXYY HOXYY GXXYY HPXYY IUXYY Part Number (Tape and Reel) 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-1.4-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 Note: Sample stock is generally held on all part numbers listed in BOLD. Note 1: XYY = assembly and date code. 3218.2004.02.1.0 15 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. 16 3218.2004.02.1.0 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. 3218.2004.02.1.0 17 AAT3218 150mA MicroPower™ High Performance LDO 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, and advise customers 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. Advanced Analogic Technologies, Inc. 830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 18 3218.2004.02.1.0