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TLV741P_1808 Datasheet(PDF) 12 Page - Texas Instruments |
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TLV741P_1808 Datasheet(HTML) 12 Page - Texas Instruments |
12 / 36 page OUT LIMIT LOAD V I R = ´ t = 120·R L 120+R L ·C OUT 12 TLV741P SBVS309 – JULY 2017 www.ti.com Product Folder Links: TLV741P Submit Documentation Feedback Copyright © 2017, Texas Instruments Incorporated 8.3 Feature Description 8.3.1 Undervoltage Lockout (UVLO) The TLV741P device uses a UVLO circuit that disables the output until the input voltage is greater than the rising UVLO voltage. The circuit ensures that the device does not exhibit any unpredictable behavior when the supply voltage is lower than the operational range of the internal circuitry, VIN(min). During UVLO disable, the output of the TLV741P version is connected to ground with a 120-Ω pulldown resistor. 8.3.2 Shutdown The enable pin (EN) is active high. Enable the device by forcing the EN pin to exceed VEN(high) (0.9 V, minimum). Turn off the device by forcing the EN pin to drop below 0.4 V. If shutdown capability is not required, connect EN to IN. The TLV741P has an internal pulldown MOSFET that connects a 120-Ω resistor to ground when the device is disabled. The discharge time after disabling depends on the output capacitance (COUT) and the load resistance (RL) in parallel with the 120-Ω pulldown resistor. The time constant is calculated in Equation 1. (1) 8.3.3 Foldback Current Limit The TLV741P device has an internal foldback current limit that helps protect the regulator during fault conditions. The current supplied by the device is gradually reduced while the output voltage decreases. When the output shorts, the LDO supplies a typical current of 40 mA. Output voltage is not regulated when the device is in current limit, and is calculated by Equation 2: (2) The PMOS pass transistor dissipates [(VIN – VOUT) × ILIMIT] until thermal shutdown is triggered and the device turns off. The internal thermal shutdown circuit turns on the device during cool down. If the fault condition continues, the device cycles between current limit and thermal shutdown. See Thermal Information for more details. The TLV741P PMOS pass element has a built-in body diode that conducts current when the voltage at OUT exceeds the voltage at IN. This current is not limited, so if extended reverse voltage operation is anticipated, TI recommends externally limiting the rated output current to 5%. 8.3.4 Thermal Protection Thermal protection disables the output when the junction temperature rises to approximately 158°C, allowing the device to cool. When the junction temperature cools to approximately 140°C, the output circuitry is again enabled. Depending on power dissipation, thermal resistance, and ambient temperature, the thermal protection circuit may cycle on and off. This cycling limits regulator dissipation, which protects the device from damage as a result of overheating. Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate heat sink. For reliable operation, junction temperature must be limited to 125°C maximum. To estimate the margin of safety in a complete design (including heat sink), increase the ambient temperature until the thermal protection is triggered; use worst-case loads and signal conditions. The TLV741P internal protection circuitry is designed to protect against overload conditions. This circuitry is not intended to replace proper heat sinking. Continuously running the TLV741P device into thermal shutdown degrades device reliability. |
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