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9 / 16 page AAT3221/2 150mA NanoPower™ LDO Linear Regulator PowerLinearTM PRODUCT DATASHEET 3221.2007.11.1.12 9 www .analogictech.com Applications Information To ensure that the maximum possible performance is obtained from the AAT3221/2, please refer to the follow- ing application recommendations. Input Capacitor A 1μF or larger capacitor is typically recommended for CIN in most applications. A CIN capacitor is not required for basic LDO regulator operation. However, if the AAT3221/2 is physically located any distance more than one or two centimeters from the input power source, a CIN capacitor will be needed for stable operation. CIN should be located as closely 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 power supply ripple rejection. Ceramic, tantalum, or aluminum electrolytic capacitors may be selected for CIN, as there is no specific capacitor ESR requirement. 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 sta- bility, 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 pos- sible for maximum device performance. The AAT3221/2 has been specifically designed to function with very low ESR ceramic capacitors. Although the device is intended to operate with these low ESR capacitors, it is stable over a wide range of capacitor ESR, thus it will also work with some higher ESR tantalum or aluminum electrolytic capacitors. However, for best performance, ceramic capacitors are recommended. The value of COUT typically ranges from 0.47μF to 10μF; however, 1μF is sufficient for most operating conditions. If large output current steps are required by an applica- tion, then an increased value for COUT should be consid- ered. The amount of capacitance needed can be calcu- lated 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 calculated using the following formula: COUT = · 15µF ΔI ΔV Where: ΔI = maximum step in output current ΔV = 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 AAT3221/2 at room temperature. The increased capacitor value is recommended if tight output toler- ances must be maintained over extreme operating con- ditions and maximum operational temperature excur- sions. If tantalum or aluminum electrolytic capacitors are used, the capacitor value should be increased to compensate for the substantial ESR inherent to these capacitor types. Capacitor Characteristics Ceramic composition capacitors are highly recommend- ed over all other types of capacitors for use with the AAT3221/2. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counter- parts. 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 capaci- tors. Since ceramic capacitors are non-polarized, they are less prone to damage if incorrectly connected. Equivalent Series Resistance (ESR) ESR is a very important characteristic to consider when selecting a capacitor. ESR is the internal series resis- tance associated with a capacitor, which includes lead resistance, internal connections, capacitor 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 C0G materials. NPO and C0G materials are typically tight tolerance and very stable over tempera- ture. Larger capacitor values are typically composed of |
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