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AAT3218 Datasheet(PDF) 9 Page - Advanced Analogic Technologies |
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AAT3218 Datasheet(HTML) 9 Page - Advanced Analogic Technologies |
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9 / 18 page  Applications Information To assure the maximum possible performance is obtained from the AAT3218, please refer to the fol- lowing application recommendations. Input Capacitor Typically, a 1µF or larger capacitor is recommend- ed for CIN in most applications. A CIN capacitor is not required for basic LDO regulator operation. However, if the AAT3218 is physically located more than three centimeters from an input power source, a CIN capacitor will be needed for stable operation. CIN should be located as close to the device VIN pin as practically possible. CIN values greater than 1µF will offer superior input line transient response and will assist in maximizing the highest possible power supply ripple rejection. Ceramic, tantalum, or aluminum electrolytic capac- itors 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 with- stand 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 func- tion 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. Bypass Capacitor and Low Noise Applications A bypass capacitor pin is provided to enhance the low noise characteristics of the AAT3218 LDO regu- lator. 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 pos- sible 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 capac- itor connection between the BYP pin and GND pin be direct and PCB traces should be as short as possi- ble. Refer to the PCB Layout Recommendations section of this datasheet for examples. There is a relationship between the bypass capac- itor 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 turn- on time will be realized when no bypass capacitor is used. DC leakage on this pin can affect the LDO regula- tor output noise and voltage regulation perform- ance. For this reason, the use of a low leakage, high quality ceramic (NPO or C0G type) or film capacitor is highly recommended. Capacitor Characteristics Ceramic composition capacitors are highly recom- mended over all other types of capacitors for use with the AAT3218. Ceramic capacitors offer many advantages over their tantalum and aluminum elec- trolytic counterparts. A ceramic capacitor typically AAT3218 150mA MicroPower™ High Performance LDO 3218.2006.04.1.8 9 |
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