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AAT4650IHS-T1 Datasheet(PDF) 9 Page - Advanced Analogic Technologies |
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AAT4650IHS-T1 Datasheet(HTML) 9 Page - Advanced Analogic Technologies |
9 / 12 page 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 for this function. Other solutions such as a poly fuse do not protect the host power supply and system from mishandling, or short circuited 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. Overcurrent and overtemperature go hand in hand. Once an overcurrent condition exists, the current supplied to the load by the AAT4650 is limited to the overcurrent 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 overtemperature circuit is activated. If the temperature reaches the maxi- mum level, the AAT4650 automatically switches off the P-channel MOSFETs. While they are off, the overtemperature 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 overcurrent cir- cuit is not activated until a lower threshold of cur- rent (approximately 700mA) is exceeded in the power device. When the load current exceeds this crude threshold, the AAT4650 quiescent current increases from 15µA to 150µA. The high speed overcurrent circuit works by linearly limiting the cur- rent when the current limit is reached. As the volt- age begins to drop on Vcc due to current limiting, the current limit magnitude varies, and generally decreases as the Vcc voltage drops to 0 volts. 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 hi impedance state. The PC card protocol for determining low voltage operations is to first power the peripheral with 5 volts and poll for 3.3 volt operation. When transitioning from 5 volts to 3.3 volts, Vcc must be discharged to less than 0.8 volts 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 100ms amount of time. 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 (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. AAT4650 5V/3V PC Card Power Switch 4650.2001.10.0.93 9 Typical PC Card Application Circuit VCC5 VCC3 CTL1 CTL0 FAULT VCC GND AAT4650 8 5 3 2 4 1 6,7 VCC Power Supply 5V 3.3V PC Card Controller PC Card Slot CTL1 CTL0 FAULT 100K Ω VCC CIN3 1 µF CIN5 1 µF COUT 0.1 µF |
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