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AAT4280AIJS-2-T1 Datasheet(PDF) 11 Page - Advanced Analogic Technologies |
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AAT4280AIJS-2-T1 Datasheet(HTML) 11 Page - Advanced Analogic Technologies |
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11 / 16 page  AAT4280A Slew Rate Controlled Load Switch SmartSwitch TM PRODUCT DATASHEET 4280A.2008.04.1.5 11 www .analogictech.com Applications Information Input Capacitor A 1μF or larger capacitor is typically recommended for CIN in most applications. A CIN capacitor is not required for basic operation; however, CIN is useful in preventing load transients from affecting upstream circuits. CIN should be located as close to the device VIN pin as practi- cally possible. Ceramic, tantalum, or aluminum electro- lytic capacitors may be selected for CIN. There is no specific capacitor ESR requirement for CIN; however, for higher current operation, ceramic capacitors are recom- mended for CIN due to their inherent capability over tan- talum capacitors to withstand input current surges from low impedance sources, such as batteries in portable devices. Output Capacitor For proper slew operation, a 0.1μF capacitor or greater between VOUT and GND is recommended. The output capacitor has no specific capacitor type or ESR require- ment. If desired, COUT may be increased without limit to accommodate any load transient condition without adversely affecting the device turn-on slew rate time. Enable Function The AAT4280A features an enable / disable function. This pin (ON/OFF) is compatible with both TTL or CMOS logic. Reverse Output-to-Input Voltage Conditions and Protection Under normal operating conditions, a parasitic diode exists between the output and input of the load switch. The input voltage should always remain greater than the output load voltage, maintaining a reverse bias on the internal para- sitic diode. Conditions where VOUT might exceed VIN should be avoided since this would forward bias the internal para- sitic diode and allow excessive current flow into the VOUT pin and possibly damage the load switch. In applications where there is a possibility of VOUT exceeding VIN for brief periods of time during normal 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 exceeding VIN for extended periods of time, it is recommended to place a Schottky diode from 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 AAT4280A is designed to deliver a continuous output load current. The limiting characteristic for maximum safe operating output load current is package power dis- sipation. 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 load switch is mounted on a printed circuit board utilizing the minimum recommended footprint, as stated in the Layout Considerations section of this datasheet. At any given ambient temperature (TA), the maximum package power dissipation can be determined by the fol- lowing equation: PD(MAX) [TJ(MAX) - TA] θ JA = Constants for the AAT4280A are maximum junction tem- perature, TJ(MAX) = 125°C, and package thermal resis- tance, ΘJA = 120°C/W. Worst case conditions are calcu- lated at the maximum operating temperature where TA = 85°C. Typical conditions are calculated under normal ambient conditions where TA = 25°C. At TA = 85°C, PD(MAX) = 333mW. At TA = 25°C, PD(MAX) = 833mW. The maximum continuous output current for the AAT4280A is a function of the package power dissipation and the RDS of the MOSFET at TJ(MAX). The maximum RDS of the MOSFET at TJ(MAX) is calculated by increasing the maximum room temperature RDS by the RDS temperature coefficient. The temperature coefficient (TC) is 2800ppm/°C. Therefore, MAX RDS125°C = RDS25°C · (1 + TC · ΔT) MAX RDS125°C = 120mΩ · (1 + 0.0028 · (125°C - 25°C)) = 154mΩ For maximum current, refer to the following equation: IOUT(MAX) PD(MAX) RDS < |
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