DATA SHEET AAT3218 150mA MicroPowerTM 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, and good power supply ripple rejection (PSRR), and is reasonably low noise, making it ideal for powering sensitive circuits with fast switching requirements. • 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 • 5 Factory-Programmed Output Voltages • SOT23 5-Pin or SC70JW 8-Pin Package 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 5 factoryprogrammed voltages: 1.2V, 2.3V, 2.8V, 2.85V, or 3.5V. Applications • Bluetooth™ Headsets • Cellular Phones • Digital Cameras • Notebook Computers • Personal Portable Electronics • Portable Communication Devices Typical Application VIN IN ON/OFF AAT3218 VOUT OUT BYP EN GND 1µF 10nF 2.2µF GND GND Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 1 DATA SHEET AAT3218 150mA MicroPowerTM High Performance LDO Pin Descriptions Pin Number SOT23-5 SC70JW-8 Symbol 1 2 5, 6 8 IN GND 3 7 EN 4 1 BYP 5 2, 3, 4 OUT Function 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. Bypass capacitor connection; to improve AC ripple rejection, connect a 10nF capacitor to GND. This will also provide a soft-start function. Output pin; should be decoupled with 2.2µF ceramic capacitor. Pin Configuration SOT23-5 (Top View) IN GND 2 EN 1 5 OUT 2 3 4 BYP SC70JW-8 (Top View) BYP OUT OUT OUT 1 8 2 7 3 6 4 5 GND EN IN IN Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 DATA SHEET AAT3218 150mA MicroPowerTM High Performance LDO Absolute Maximum Ratings1 TA = 25°C, unless otherwise noted. Symbol VIN VENIN(MAX) IOUT TJ Description 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 mA °C Rating Units 190 526 °C/W mW Rating Units (VOUT+VDO) to 5.5 -40 to +85 V °C V Thermal Information2 Symbol Description Maximum Thermal Resistance (SOT23-5, SC70JW-8) Maximum Power Dissipation (SOT23-5, SC70JW-8) QJA PD Recommended Operating Conditions Symbol VIN T Description Input Voltage Ambient Temperature Range 3 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. 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 3 DATA SHEET AAT3218 150mA MicroPowerTM 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 VOUT IOUT VDO ISC IQ ISD DVOUT/ VOUT*DVIN Description Conditions Output Voltage Tolerance IOUT = 1mA to 150mA Output Current Dropout Voltage1, 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 Line Regulation VIN = VOUT + 1 to 5.0V DVOUT(line) Dynamic Line Regulation DVOUT(load) tENDLY VEN(L) VEN(H) IEN Dynamic Load Regulation Enable Delay Time Enable Threshold Low Enable Threshold High Leakage Current on Enable Pin PSRR TSD THYS eN TC Power Supply Rejection Ratio Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Output Noise Output Voltage Temperature Coefficient Min TA = 25°C TA = -40°C to 85°C Typ -1.5 -2.5 150 200 600 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 % 300 mA mV mA 125 1 µA 0.09 %/V 2.5 mV 30 15 µs 0.6 1.5 VEN = 5V IOUT = 10mA, CBYP = 10nF 1 1 kHz 10kHz 1MHz 67 47 45 145 12 Noise Power BW = 300Hz - 50kHz µA dB °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 V Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 DATA SHEET AAT3218 150mA MicroPowerTM High Performance LDO Typical Characteristics Unless otherwise noted, VIN = 5V, TA = 25°C. Dropout Characteristics 3.20 260 240 220 200 180 160 140 120 100 80 60 40 20 0 3.00 IL = 150mA Output Voltage (V) Dropout Voltage (mV) Dropout Voltage vs. Temperature IL = 100mA IL = 50mA -40 -30 -20 -10 0 IOUT = 0mA 2.80 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 3.00 3.10 3.20 Ground Current vs. Input Voltage 90.00 Ground Current (µA) 300 Dropout Voltage (mV) 2.80 Input Voltage (V) Dropout Voltage vs. Output Current 250 200 85°C 150 100 25°C -40°C 50 80.00 70.00 60.00 50.00 0 25 50 75 IOUT = 150mA 40.00 IOUT = 50mA IOUT = 0mA 30.00 IOUT = 10mA 20.00 10.00 0 100 125 0.00 150 Output Current (mA) 2 2.5 3 3.5 4 4.5 5 Input Voltage (V) Quiescent Current vs. Temperature Output Voltage vs. Temperature 1.203 100 90 1.202 80 Output Voltage (V) Quiescent Current (µA) IOUT = 10mA 70 60 50 40 30 20 10 0 -40 -30 -20 -10 0 1.200 1.199 1.198 1.197 1.196 -40 -30 -20 -10 10 20 30 40 50 60 70 80 90 100 110 120 Temperature (°C) 1.201 0 10 20 30 40 50 60 70 80 90 100 Temperature (°C) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 5 DATA SHEET AAT3218 150mA MicroPowerTM High Performance LDO Typical Characteristics Unless otherwise noted, VIN = 5V, TA = 25°C. Load Transient Response Over-Current Protection 2.90 Output Voltage (V) 1000 800 600 400 200 0 2.85 VOUT 400 2.80 300 2.75 200 2.70 100 2.65 -200 Time (20ms/div) 500 2.60 0 IOUT -100 Time (100µs/div) AAT3218 Self Noise VIH and V IL vs. VIN Noise Amplitude (µV/rtHz) (COUT = 10µF, 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 0.1 1 10 VIL 1.100 1.075 1.050 2.5 0.001 0.01 100 Frequency (kHz) 1000 10000 3.0 3.5 4.0 4.5 Input Voltage (V) 6 Output Current (mA) Output Current (mA) 1200 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 5.0 5.5 DATA SHEET AAT3218 150mA MicroPowerTM 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 fast-start control circuit, which accelerates the power-up 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. GND 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 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 7 DATA SHEET AAT3218 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. 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. 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. 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. 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 turnoff time are desired, the value of CBYP should be reduced. Output Capacitor 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. 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 than 10mA, the minimum value for COUT can be as low as 0.47µF. 8 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. 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 nonpolarized. 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 ambi- Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 DATA SHEET AAT3218 150mA MicroPowerTM High Performance LDO ent 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. 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 1.5kW resistor is connected between VOUT and GND. This is intended to discharge COUT when the LDO regulator is disabled. The internal 1.5kW 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 allows 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 no-load 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 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 9 DATA SHEET AAT3218 150mA MicroPowerTM High Performance LDO 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. 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: [TJ(MAX) - TA] PD(MAX) = ΘJA Constants for the AAT3218 are TJ(MAX), the maximum junction temperature for the device which is 125°C and QJA = 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 = 2.8V, and TA = 25°C, IOUT(MAX) < 240mA. If the output load current were to exceed 240mA 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. 10 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 · IGND This formula can be solved for VIN to determine the maximum input voltage. VIN(MAX) = PD(MAX) + VOUT · IOUT IOUT · IGND The following is an example for an AAT3218 set for a 2.3V output: VOUT = 2.3V IOUT = 150mA IGND = 150µA VIN(MAX) = 526mW + 2.3V ∙ 150mA 150mA + 150µA VIN(MAX) = 5.8V From the discussion above, PD(MAX) was determined to equal 526mW at TA = 25°C. Thus, the AAT3218 can sustain a constant 2.3V output at a 150mA load current as long as VIN is ≤ 5.8V at an ambient temperature of 25°C. 5.8V 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 2.3V output at 85°C: VOUT = 2.3V IOUT = 150mA IGND = 150µA VIN(MAX) = 211mW + 2.3V ∙ 150mA 150mA + 150µA VIN(MAX) = 3.7V Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 DATA SHEET AAT3218 150mA MicroPowerTM High Performance LDO 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 = 2.3V at a 150mA load and TA = 85°C. VIN is greater than 3.7V, which is the maximum safe continuous input level for VOUT = 2.3V 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 = 2.3V %DC = PD(MAX) (VIN - VOUT) ∙ IOUT + VIN ∙ IGND %DC = 211mW (4.2V - 2.3V) ∙ 150mA + 4.2V ∙ 150µA %DC = 73.87% For a 150mA output current and a 2.5V drop across the AAT3218 at an ambient temperature of 85°C, the maximum on-time duty cycle for the device would be 73.87%. High Peak Output Current Applications Some applications require the LDO regulator to operate at continuous nominal level with short duration, highcurrent 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. For example, a 2.3V system using an AAT3218IGV2.3-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. 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 · IGND PD(100mA) = (4.2V - 2.3V) · 100mA + 4.2V · 150µA PD(100mA) = 190.6mW PD(91.8%D/C) = %DC · PD(100mA) PD(91.8%D/C) = 0.918 x 190.6mW PD(91.8%D/C) = 175mW The power dissipation for a 100mA load occurring for 91.8% of the duty cycle will be 175mW. 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 · IGND PD(150mA) = (4.2V - 2.3V) · 150mA + 4.2V · 150mA PD(150mA) = 285.6mW PD(8.2%D/C) = %DC x PD(150mA) PD(8.2%D/C) = 0.082 x 285.6mW PD(8.2%D/C) = 23.4mW The power dissipation for a 150mA load occurring for 8.2% of the duty cycle will be 23.4mW. 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) = 175mW + 23.4mW PD(total) = 198.4mW 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 198.4mW. This is well within the thermal limits for safe operation of the device. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 11 DATA SHEET AAT3218 150mA MicroPowerTM High Performance LDO Printed Circuit Board Layout Recommendations 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 highperformance applications, this method is not recommended. 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. 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. 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. 12 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. 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 DATA SHEET AAT3218 150mA MicroPowerTM High Performance LDO ILOAD IIN VIN VIN LDO VOUT Regulator EN 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. 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 13 DATA SHEET AAT3218 150mA MicroPowerTM High Performance LDO Ordering Information Output Voltage Package 1.2V 2.3V 2.8V 2.85V 3.5V 1.2V 2.3V 3.5V Marking1 Part Number (Tape and Reel)2 KWXYY AAT3218IGV-1.2-T1 AAT3218IGV-2.3-T1 AAT3218IGV-2.8-T1 AAT3218IGV-2.85-T1 AAT3218IGV-3.5-T1 AAT3218IJS-1.2-T1 AAT3218IJS-2.3-T1 AAT3218IJS-3.5-T1 SOT23-5 EMXYY HOXYY KWXYY SC70JW-8 Skyworks Green™ products are compliant with all applicable legislation and are halogen-free. For additional information, refer to Skyworks Definition of Green™, document number SQ04-0074. 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. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 14 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 DATA SHEET AAT3218 150mA MicroPowerTM 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. Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved. 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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202249A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012 15