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AAT4601IHS-B1 Datasheet(PDF) 9 Page - Advanced Analogic Technologies |
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AAT4601IHS-B1 Datasheet(HTML) 9 Page - Advanced Analogic Technologies |
9 / 14 page AAT4601 1.5A Current Limited P-Channel Switch 4601.2001.11.0.92 9 Applications Information Operation in Current Limit If an excessive load is applied to the output of an AAT4601, the load's current will be limited by the AAT4601's current limit circuitry. Refer to the figure named "Overload Operation". If a short circuit were to occur on the load, it would demand more current than what is allowed by the internal current limiting circuit and the voltage at the AAT4601's output will drop. This causes the AAT4601 to dissipate more power than in normal operation, causing the die tem- perature to increase. When die temperature exceeds the internal over temperature threshold, the AAT4601 will shut down. After shutting down, the AAT4601 cools to a level below the over temperature thresh- old, at which point it will start up again. The AAT4601 will continue to cycle off and on until one of the fol- lowing events occurs; the load current is reduced to a level below the AAT4601's current limit setting, the input power is removed, or until the output is turned off by a logic high level applied to the ON pin. Thermal Considerations Since the AAT4601 has internal current limit and over temperature protection, junction temperature is rarely a concern. If an application requires a large load current in a high temperature operating envi- ronment, there is the possibility that the over tem- perature protection circuit rather than the current limit circuit will regulate the current available to the load. In these applications, the maximum current available without risk of activation of the over tem- perature circuit can be calculated. The maximum internal temperature while current limit is not active can be calculated using Equation 1: TJ(MAX) = IMAX 2 × R DS(ON)(MAX) × R θJA + TA(MAX) In Equation 1, IMAX is the maximum current required by the load. RDS(ON)(MAX) is the maximum rated RDS(ON) of the AAT4601 at high temperature. RθJA is the thermal resistance between the AAT4601's die and the board onto which it is mounted. TA(MAX) is the maximum ambient temperature for the printed circuit board assembly under the AAT4601 when the load switch is not dissipating power. Equation 1 can be transformed to provide IMAX; Refer to Equation 2. IMAX= TSD(MIN) - TA(MAX) RDS(ON)(MAX) × RθJA TSD(MIN) is the minimum temperature required to activate the AAT4601's over temperature protec- tion. With typical specification of 125°C, 115°C is a safe minimum value to use. For example, a portable device is specified to oper- ate in a 50°C environment. The printed circuit board assembly will operate at temperatures as high as 85°C. This portable device has a sealed case and the area of the printed board assembly is rellatively small causing RθJA to be approximately 120°C/W. Using Equation 2, IMAX= 115 - 85 = 1.4 A 130 × 120 If this system requires less than 1.4 A, the thermal limit will not activate during normal operation. Overload Operation 0 1 2 3 4 5 6 -0.5 0 0.5 1 1.5 2 Time (s) Output Voltage Input Voltage 1 9 is applied to output at t = 0 R SET is 2 k9 |
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