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TPS254900A-Q1 Datasheet(PDF) 22 Page - Texas Instruments |
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TPS254900A-Q1 Datasheet(HTML) 22 Page - Texas Instruments |
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OS(max) 0.9987 (ILIM _ xx) 51 820 V I (mA) 38 R k = + W OS(min) 0.9974 (ILIM _ xx) 46 464 V I (mA) 32 R k = - W OS(nom) 0.9945 (ILIM _ xx) 48 687 V I (mA) R k = W 22 TPS254900A-Q1 SLUSCU5A – NOVEMBER 2017 – REVISED JANUARY 2018 www.ti.com Product Folder Links: TPS254900A-Q1 Submit Documentation Feedback Copyright © 2017–2018, Texas Instruments Incorporated 8.3.8 Undervoltage Lockout The undervoltage-lockout (UVLO) circuit disables the power switch until the input voltage reaches the UVLO turnon threshold. Built-in hysteresis prevents unwanted oscillations on the output due to input voltage drop from large current surges. 8.3.9 Thermal Sensing Two independent thermal-sensing circuits protect the TPS254900A-Q1 device if the temperature exceeds recommended operating conditions. These circuits monitor the operating temperature of the power-distribution switch and disable operation. The power dissipation in the package is proportional to the voltage drop across the power switch, so the junction temperature rises during an overcurrent condition. The first thermal sensor turns off the power switch when the die temperature exceeds 135ºC and the device is in current limit. The second thermal sensor turns off the power switch when the die temperature exceeds 155ºC regardless of whether the power switch is in current limit. Hysteresis is built into both thermal sensors, and the switch turns on after the device has cooled by approximately 20°C. The switch continues to cycle off and then on until the fault is removed. The open-drain false-reporting output, FAULT, is asserted (low) during an overtemperature shutdown condition. 8.3.10 Current-Limit Setting The TPS254900A-Q1 has two independent current-limit settings that are each adjusted externally with a resistor. The ILIM_HI setting is adjusted with R(ILIM_HI) connected between ILIM_HI and GND. The ILIM_LO setting is adjusted with R(ILIM_LO) connected between ILIM_LO and GND. Consult the device truth table (Table 3) to see when each current limit is used. Both settings have the same relation between the current limit and the adjusting resistor. The following equation calculates the value of resistor for adjusting the typical current limit: (3) Many applications require that the current limit meet specific tolerance limits. When designing to these tolerance limits, both the tolerance of the TPS254900A-Q1 current limit and the tolerance of the external adjusting resistor must be taken into account. The following equations approximate the TPS254900A-Q1 minimum and maximum current limits to within a few milliamperes and are appropriate for design purposes. The equations do not constitute part of TI’s published device specifications for purposes of TI’s product warranty. These equations assume an ideal—no variation—external adjusting resistor. To take resistor tolerance into account, first determine the minimum and maximum resistor values based on its tolerance specifications and use these values in the equations. Because of the inverse relation between the current limit and the adjusting resistor, use the maximum resistor value in the IOS(min) equation and the minimum resistor value in the IOS(max) equation. (4) (5) |
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