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AAT3220IQY-35-T1 Datasheet(PDF) 10 Page - Advanced Analogic Technologies |
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AAT3220IQY-35-T1 Datasheet(HTML) 10 Page - Advanced Analogic Technologies |
10 / 16 page AAT3220 150mA NanoPower™ LDO Linear Regulator 10 3220.2001.09.1.0 ceramic capacitors, typically greater than 2.2µF are often available in the low cost Y5V and Z5U dielec- trics. These two material types are not recommend- ed for use with LDO regulators since the capacitor tolerance can vary by 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 prob- lems for circuit operation and stability. X7R and X5R dielectrics are much more desirable. The tempera- ture tolerance of X7R dielectric is better than ±15%. Capacitor area is another contributor to ESR. Capacitors, which are physically large in size will have a lower ESR when compared to a smaller sized capacitor of equivalent material and capaci- tance value. These larger devices can also improve circuit transient response when compared to an equal value capacitor in a smaller package size. Consult capacitor vendor data sheets carefully when selecting capacitors for use with LDO regulators. Short Circuit Protection and Thermal Protection The AAT3220 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 maxi- mum rated output. If a short circuit condition were to continually draw more than the current limit threshold, the LDO regulator's output 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 AAT3220's die temperature will increase rapidly. Once the regulator's power dissipation capacity has been exceeded and the internal die temperature reaches approximately 140°C the system thermal protection circuit will become active. The internal thermal protection cir- cuit will actively turn off the LDO regulator output pass device to prevent the possibility of over tem- perature damage. The LDO regulator output will remain in a shutdown state until the internal die temperature falls back below the 140°C trip point. The combination and interaction between the short circuit and thermal protection systems allow the LDO regulator to withstand indefinite short circuit conditions without sustaining permanent damage. No-Load Stability The AAT3220 is designed to maintain output volt- age regulation and stability under operational no- load conditions. 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 for recom- mended typical output capacitor values. Thermal Considerations and High Output Current Applications The AAT3220 is designed to deliver a continuous output load current of 150mA under normal operat- ing conditions. The limiting characteristic for the maximum output load safe operating area is essen- tially package power dissipation and the internal pre- set 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 reg- ulator is mounted on a printed circuit board utilizing the minimum recommended footprint and the print- ed circuit board is 0.062 inch thick FR4 material with one ounce copper. At any given ambient temperature (TA) the maxi- mum package power dissipation can be deter- mined by the following equation: PD(MAX) = [TJ(MAX) - TA] / Θ JA Constants for the AAT3220 are TJ(MAX), the maxi- mum junction temperature for the device which is 125°C and Θ JA = 200°C/W, the package thermal resistance. Typically, maximum conditions are cal- culated at the maximum operating temperature where TA = 85°C, under normal ambient conditions TA = 25°C. Given TA = 85°C, the maximum pack- age power dissipation is 200mW. At TA = 25°C°, the maximum package power dissipation is 500mW. The maximum continuous output current for the AAT3220 is a function of the package power dissi- pation and the input to output voltage drop across the LDO regulator. Refer to the following simple equation: IOUT(MAX) < PD(MAX) / (VIN - VOUT) |
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