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AAT3218IJS-1.25-T1 Datasheet(PDF) 10 Page - Advanced Analogic Technologies |
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AAT3218IJS-1.25-T1 Datasheet(HTML) 10 Page - Advanced Analogic Technologies |
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10 / 18 page  AAT3218 150mA MicroPower™ High Performance LDO 10 3218.2006.04.1.8 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. 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 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. 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 volt- age 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 1.5k Ω resistor is connected between VOUT and GND. This is intended to discharge COUT when the LDO regulator is disabled. The internal 1.5k Ω has no adverse effect on device turn-on time. Short-Circuit Protection The AAT3218 contains an internal short-circuit pro- tection circuit that will trigger when the output load current exceeds the internal threshold limit. Under short-circuit conditions, the output of the LDO reg- ulator will be current limited until the short-circuit condition is removed from the output or LDO regu- lator package power dissipation exceeds the device thermal limit. Thermal Protection The AAT3218 has an internal thermal protection cir- cuit which will turn on when the device die temper- ature exceeds 150°C. The internal thermal protec- tion 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. |
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