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AAT3237IJS-2.8-T1 Datasheet(PDF) 9 Page - Advanced Analogic Technologies |
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AAT3237IJS-2.8-T1 Datasheet(HTML) 9 Page - Advanced Analogic Technologies |
9 / 13 page Applications Information To assure the maximum possible performance is obtained from the AAT3237, please refer to the fol- lowing application recommendations. Input Capacitor Typically, a 1µF or larger capacitor is recommend- ed for C IN in most applications. A C IN capacitor is not required for basic LDO regulator operation. However, if the AAT3237 is physically located more than three centimeters from an input power source, a C IN capacitor will be needed for stable operation. C IN should be located as closely to the device VIN pin as practically possible. C IN 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 C IN. There is no specific capacitor ESR requirement for C IN. However, for 300mA LDO regulator output operation, ceramic capacitors are recommended for C IN 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 V OUT and GND. The C OUT capacitor connection to the LDO regulator ground pin should be made as direct as practically possible for maximum device performance. The AAT3237 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 AAT3237 should use 2.2µF or greater for C OUT. If desired, COUT may be increased without limit. In low output current applications where output load is less than 10mA, the minimum value for C OUT can be as low as 0.47µF. Capacitor Characteristics Ceramic composition capacitors are highly recom- mended over all other types of capacitors for use with the AAT3237. Ceramic capacitors offer many advantages over their tantalum and aluminum elec- trolytic counterparts. A ceramic capacitor typically has very low ESR, is lower cost, has a smaller PCB footprint, and is non-polarized. Line and load tran- sient 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 asso- ciated with a capacitor that includes lead resistance, internal connections, size and area, material compo- sition, and ambient temperature. Typically, capacitor ESR is measured in milliohms for ceramic capacitors and can range to more than several ohms for tanta- lum or aluminum electrolytic capacitors. Ceramic Capacitor Materials: Ceramic capaci- tors less than 0.1µF are typically made from NPO or C0G materials. NPO and C0G materials gener- ally have tight tolerance and are very stable over temperature. Larger capacitor values are usually composed of X7R, X5R, Z5U, or Y5V dielectric materials. These two material types are not recom- mended 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 tran- sient response when compared to an equal value capacitor in a smaller package size. Consult capacitor vendor datasheets carefully when selecting capacitors for LDO regulators. AAT3237 300mA MicroPower™ LDO with PowerOK 3237.2006.01.1.4 9 |
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