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AAT3223IGU-2.85-T1 Datasheet(PDF) 10 Page - Advanced Analogic Technologies |
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AAT3223IGU-2.85-T1 Datasheet(HTML) 10 Page - Advanced Analogic Technologies |
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10 / 17 page  AAT3223 250mA NanoPower™ LDO Linear Regulator with Power-OK 10 3223.2005.04.1.4 Applications Information To assure the maximum possible performance is obtained from the AAT3223, 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 AAT3223 is physically located any distance more than one or two centimeters from the input power source, a C IN capacitor will be needed for stable operation. C IN should be located as closely to the device V IN pin as practically pos- sible. C IN values greater than 1µF will offer superi- or input line transient response and will assist in maximizing the power supply ripple rejection. Ceramic, tantalum, or aluminum electrolytic capac- itors may be selected for C IN, as there is no specif- ic capacitor ESR requirement. For 250mA LDO regulator output operation, ceramic capacitors are recommended for C IN due to their inherent capabil- ity over tantalum capacitors to withstand input cur- rent 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 per- formance. The AAT3223 has been specifically designed to function with very low ESR ceramic capacitors. Although the device is intended to oper- ate with these low ESR capacitors, it is stable over a very wide range of capacitor ESR, thus it will also work with some higher ESR tantalum or aluminum electrolytic capacitors. However, for best perform- ance, ceramic capacitors are recommended. The value of C OUT typically ranges from 0.47µF to 10µF; however, 1µF is sufficient for most operating conditions. If large output current steps are required by an application, then an increased value for C OUT should be considered. The amount of capacitance needed can be calculated from the step size of the change in output load current expected and the voltage excursion that the load can tolerate. The total output capacitance required can be cal- culated using the following formula: Where: ∆I = maximum step in output current ∆V = maximum excursion in voltage that the load can tolerate Note that use of this equation results in capacitor values approximately two to four times the typical value needed for an AAT3223 at room temperature. The increased capacitor value is recommended if tight output tolerances must be maintained over extreme operating conditions and maximum opera- tional temperature excursions. If tantalum or alu- minum electrolytic capacitors are used, the capaci- tor value should be increased to compensate for the substantial ESR inherent to these capacitor types. Capacitor Characteristics Ceramic composition capacitors are highly recom- mended over all other types of capacitors for use with the AAT3223. 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 less prone to damage if incorrectly connected. 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, capacitor size and area, material composition, and ambient tempera- ture. Typically, capacitor ESR is measured in mil- liohms for ceramic capacitors and can range to more than several ohms for tantalum or aluminum electrolytic capacitors. COUT = × 15µF ∆I ∆V |
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