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AAT4650 Datasheet(PDF) 9 Page - Advanced Analogic Technologies |
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AAT4650 Datasheet(HTML) 9 Page - Advanced Analogic Technologies |
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9 / 14 page  AAT4650 5V/3V PC Card Power Switch 4650.2006.05.1.2 9 Thermal issues are not a problem in the SOP-8 package since ΘJA, the package thermal resistance, is only 120°C/W. At any given ambient temperature (TA) the maximum package power dissipation can be determined by the following equation: Constants for the AAT4650 are maximum junction temperature, TJ(MAX) = 125°C, and package thermal resistance, ΘJA = 120°C/W. Worst case conditions are calculated at the maximum operating tempera- ture where TA = 85°C. Typical conditions are cal- culated under normal ambient conditions where TA = 25°C. At TA = 85°C, PD(MAX) = 333mW. At TA = 25°C, PD(MAX) = 833mW. Maximum current is given by the following equation: For the AAT4650 at 85°C, IOUT(MAX) = 1.65A, a value greater than the internal minimum current limit specification. Over-Current and Over-Temperature Protection Because many AAT4650 applications provide power to external devices, it is designed to protect its host device from malfunctions in those peripherals through slew rate control, current limiting, and ther- mal limiting. The AAT4650 current limit and thermal limit serve as an immediate and reliable electronic fuse without any increase in RDS(ON) for this function. Other solutions, such as a poly fuse, do not protect the host power supply and system from mishandling or short circuiting peripherals; they will only prevent a fire. The AAT4650 high-speed current limit and thermal limit not only prevent fires, they also isolate the power supply and entire system from any activi- ty at the external port and report a mishap by means of a FAULT signal. Over-current and over-temperature go hand in hand. Once an over-current condition exists, the current supplied to the load by the AAT4650 is limited to the over-current threshold. This results in a voltage drop across the AAT4650 which causes excess power dissipation and a package temperature increase. As the die begins to heat up, the over-temperature cir- cuit is activated. If the temperature reaches the max- imum level, the AAT4650 automatically switches off the P-channel MOSFETs. While they are off, the over-temperature circuit remains active. Once the temperature has cooled by approximately 10°C, the P-channel MOSFETs are switched back on. In this manner, the AAT4650 is thermally cycled on and off until the short circuit is removed. Once the short is removed, normal operation automatically resumes. To save power, the full high-speed over-current cir- cuit is not activated until a lower threshold of cur- rent (approximately 500mA) is exceeded in the power device. When the load current exceeds this crude threshold, the AAT4650 quiescent current increases from 15µA to 200µA. The high-speed over-current circuit works by linearly limiting the current when the current limit is reached. As the voltage begins to drop on VCC due to current limit- ing, the current limit magnitude varies and general- ly decreases as the VCC voltage drops to 0V. Switching VCC Voltage The AAT4650 meets PC card standards for switch- ing the VCC output by providing a ground path for VCC, as well as a high impedance state. The PC card protocol for determining low voltage opera- tions is to first power the peripheral with 5V and poll for 3.3V operation. When transitioning from 5V to 3.3V, VCC must be discharged to less than 0.8V to provide a hard reset. The resistive ground state (CTL1 = 0, CTL0 = 0) will accommodate this. The ground state will also guarantee the VCC voltage to be discharged within the specified amount of time (100ms). Printed Circuit Board Layout Recommendations For proper thermal management, to minimize PCB trace resistance, and to take advantage of the low RDS(ON) of the AAT4650, a few circuit board layout rules should be followed: VCC3, VCC5, and VCC should be routed using wider than normal traces; the two VCC pins (Pins 6 and 7) should be connected to the same wide PCB trace; and GND should be connect- ed to a ground plane. For best performance, CIN and COUT should be placed close to the package pins. = I OUT(MAX) P D(MAX) R DS(ON) P D(MAX) = T J(MAX) -TA θJA |
Similar Part No. - AAT4650_06 |
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Similar Description - AAT4650_06 |
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