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AAT3242ITP-QY-T1 Datasheet(PDF) 11 Page - Advanced Analogic Technologies |
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AAT3242ITP-QY-T1 Datasheet(HTML) 11 Page - Advanced Analogic Technologies |
11 / 15 page AAT3242 300mA/150mA Dual CMOS LDO Linear Regulator PowerLinearTM PRODUCT DATASHEET 3242.2008.08.1.11 11 www .analogictech.com Short-Circuit Protection The AAT3242 contains internal short-circuit protection that will trigger when the output load current exceeds the internal threshold limit. Under short-circuit condi- tions, the output of the LDO regulator will be current limited until the short-circuit condition is removed from the output or LDO regulator package power dissipation exceeds the device thermal limit. Thermal Protection The AAT3242 has an internal thermal protection circuit which will turn on when the device die temperature exceeds 145°C. The LDO regulator output will remain in a shutdown state until the internal die temperature falls back below the 145°C trip point. The combination and interaction between the short-circuit and thermal pro- tection systems allows the LDO regulators to withstand indefinite short-circuit conditions without sustaining per- manent damage. No-Load Stability The AAT3242 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. Reverse Output-to-Input Voltage Conditions and Protection Under normal operating conditions, a parasitic diode exists between the output and input of the LDO regula- tor. The input voltage should always remain greater than the output load voltage maintaining a reverse bias on the internal parasitic diode. Conditions where VOUT might exceed VIN should be avoided since this would forward bias the internal parasitic diode and allow excessive cur- rent flow into the VOUT pin, possibly damaging the LDO regulator. In applications where there is a possibility of VOUT exceeding VIN for brief amounts of time during nor- mal operation, the use of a larger value CIN capacitor is highly recommended. A larger value of CIN with respect to COUT will effect a slower CIN decay rate during shut- down, thus preventing VOUT from exceeding VIN. In appli- cations where there is a greater danger of VOUT exceed- ing VIN for extended periods of time, it is recommended to place a Schottky diode across VIN to VOUT (connecting the cathode to VIN and anode to VOUT). The Schottky diode forward voltage should be less than 0.45V. Thermal Considerations and High Output Current Applications The AAT3242 is designed to deliver continuous output load currents of 300mA and 150mA under normal oper- ations, and can supply up to 500mA during circuit start- up conditions. This is desirable for circuit applications where there might be a brief high in-rush current during a power-on event. The limiting characteristic for the maximum output load current safe operating area is essentially package power dissipation and the internal preset thermal limit of the device. In order to obtain high operating currents, care- ful 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 mini- mum recommended footprint as stated in the layout considerations section of this document. At any given ambient temperature (TA), the maximum package power dissipation can be determined by the following equa- tion: P D(MAX) = T J(MAX) - TA θJA Constants for the AAT3242 are TJ(MAX) (the maximum junction temperature for the device, which is 125°C) and θJA = 110°C/W (the package thermal resistance). Typically, maximum conditions are calculated at the maximum operating temperature of TA = 85°C and under normal ambient conditions where TA = 25°C. Given TA = 85°C, the maximum package power dissipa- tion is 364mW. At TA = 25°C, the maximum package power dissipation is 909mW. The maximum continuous output current for the AAT3242 is a function of the package power dissipation and the input-to-output voltage drop across the LDO regulator. To determine the maximum output current for a given output voltage, refer to the following equation. This cal- culation accounts for the total power dissipation of the LDO regulator, including that caused by ground current. P D(MAX) = [(VIN - VOUTA)IOUTA + (VIN x IGND)] + [(VIN - VOUTB)IOUTB + (VIN x IGND)] |
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