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AAT3221IGV-2.3-T1 Datasheet(PDF) 10 Page - Advanced Analogic Technologies |
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AAT3221IGV-2.3-T1 Datasheet(HTML) 10 Page - Advanced Analogic Technologies |
10 / 16 page AAT3221/2 150mA NanoPower™ LDO Linear Regulator PowerLinearTM PRODUCT DATASHEET 10 3221.2007.11.1.12 www .analogictech.com X7R, X5R, Z5U, and Y5V dielectric materials. Large ceramic capacitors, typically 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 the full operating temperature range. This can cause problems for circuit operation and stability. 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 equiva- lent material and capacitance value. These larger devic- es can also improve circuit transient response when compared to an equal value capacitor in a smaller pack- age size. Consult capacitor vendor datasheets carefully when selecting capacitors for use with LDO regulators. Enable Function The AAT3221/2 features an LDO regulator enable / dis- able function. This pin (EN) is compatible with CMOS logic. Active high or active low options are available (see Ordering Information). For a logic high signal, the EN control level must be greater than 2.4 volts. A logic low signal is asserted when the voltage on the EN pin falls below 0.6 volts. For example, the active high version AAT3221/2 will turn on when a logic high is applied to the EN pin. If the enable function is not needed in a spe- cific application, it may be tied to the respective voltage level to keep the LDO regulator in a continuously on state; e.g., the active high version AAT3221/2 will tie VIN to EN to remain on. Short-Circuit Protection and Thermal Protection The AAT3221/2 is protected by both current limit and over-temperature protection circuitry. The internal short- circuit current limit is designed to activate when the output load demand exceeds the maximum rated output. If a short-circuit condition were to continually draw more than the current limit threshold, the LDO regulator’s out- put voltage will drop to a level necessary to supply the current demanded by the load. Under short-circuit or other over-current operating conditions, the output volt- age will drop and the AAT3221/2 die temperature will rapidly increase. Once the regulator’s power dissipation capacity has been exceeded and the internal die tem- perature reaches approximately 140°C, the system ther- mal protection circuit will become active. The internal thermal protection 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 tem- perature falls back below the 140°C trip point. The interaction between the short-circuit and thermal protection systems allows the LDO regulator to with- stand indefinite short-circuit conditions without sustain- ing permanent damage. No-Load Stability The AAT3221/2 is designed to maintain output voltage regulation and stability under operational no-load condi- tions. This is an important characteristic for applications where the output current may drop to zero. An output capacitor is required for stability under no-load operating conditions. Refer to the output capacitor considerations section of this document for recommended typical out- put capacitor values. Thermal Considerations and High Output Current Applications The AAT3221/2 is designed to deliver a continuous out- put load current of 150mA under normal operating con- ditions. The limiting characteristic for the maximum output load safe operating area is essentially package power dissipation and the internal preset thermal limit of the device. In order to obtain high operating currents, careful device layout and circuit operating conditions need to be taken into account. The following discussions will assume the LDO regulator is mounted on a printed circuit board utilizing the minimum recommended foot- print and the printed circuit board is 0.062-inch thick FR4 material with one ounce copper. At any given ambient temperature (TA), the maximum package power dissipation can be determined by the fol- lowing equation: PD(MAX) = TJ(MAX) - TA θJA Constants for the AAT3221/2 are TJ(MAX), the maximum junction temperature for the device which is 125°C and ΘJA = 150°C/W, the package thermal resistance. Typically, |
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