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AAT4252A Datasheet(PDF) 9 Page - Advanced Analogic Technologies |
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AAT4252A Datasheet(HTML) 9 Page - Advanced Analogic Technologies |
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9 / 14 page  AAT4252A Dual Slew Rate Controlled Load Switch 4252A.2007.06.1.0 9 Functional Description The AAT4252A is a family of flexible dual P-chan- nel MOSFET power switches designed for high- side load switching applications. There are three versions of the AAT4252A with different turn-on and turn-off characteristics to choose from, depending upon the specific requirements of an application. The first version, the AAT4252A-1, has a moderate turn-on slew rate feature, which reduces in-rush current when the MOSFET is turned on. This func- tion allows the load switch to be implemented with either a small input capacitor or no input capacitor at all. During turn-on slewing, the current ramps linearly until it reaches the level required for the output load condition. The proprietary turn-on cur- rent control method works by careful control and monitoring of the MOSFET gate voltage. When the device is switched ON, the gate voltage is quickly increased to the threshold level of the MOSFET. Once at this level, the current begins to slew as the gate voltage is slowly increased until the MOSFET becomes fully enhanced. Once it has reached this point the gate is quickly increased to the full input voltage and the R DS(ON) is minimized. The second version, the AAT4252A-2, is a very fast switch intended for high-speed switching applications. This version has no turn-on slew rate control and no special output discharge features. The final switch version, the AAT4252A-3, has the addition of a minimized slew rate limited turn-on function and a shutdown output discharge circuit to rapidly turn off a load when the load switch is dis- abled through the ON/OFF pin. Using the FAST input pin on the AAT4252A-3, the device can be manually switched to a slower slew rate. All versions of the AAT4252A operate with input voltages ranging from 1.5V to 6.5V. All versions of this device have extremely low operating current, making them ideal for battery-powered applications. The ON/OFF control pin is TTL compatible and will also function with 2.5V to 5V logic systems, mak- ing the AAT4252A an ideal level-shifting load switch. Applications Information Input Capacitor A 1μF or larger capacitor is typically recommended for C IN in most applications. A CIN capacitor is not required for basic operation; however, it is useful in preventing load transients from affecting upstream circuits. C IN should be located as close to the device VIN pin as practically possible. Ceramic, tantalum, or aluminum electrolytic capacitors may be selected for C IN. There is no specific capacitor equivalent series resistance (ESR) requirement for C IN. However, for higher current C IN, ceramic capacitors are recommended for CIN due to their inherent capability over tantalum capacitors to with- stand 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 is required between V OUT and GND. Likewise, with the output capacitor, there is no spe- cific capacitor ESR requirement. If desired, C OUT may be increased without limit to accommodate any load transient condition without adversely affecting the slew rate. Enable Function The AAT4252A features an enable / disable func- tion. This pin (ON) is active high and is compatible with TTL or CMOS logic. To assure the load switch will turn on, the ON control level must be greater than 2.0V. The load switch will go into shutdown mode when the voltage on the ON pin falls below 0.8V. When the load switch is in shutdown mode, the OUT pin is tri-stated, and quiescent current drops to leakage levels below 1μA. 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 parasitic diode. Conditions where V OUT might exceed VIN should be avoided since this would forward bias the internal parasitic diode and allow excessive current flow into |
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