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LP3982ILD-ADJ Datasheet(PDF) 11 Page - Texas Instruments |
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LP3982ILD-ADJ Datasheet(HTML) 11 Page - Texas Instruments |
11 / 23 page -t = CDELAY - VO VREF RPln 1 + - SHDN GND IN OUT LP3982 FAULT 100k VIN CC LMC7225 RESET CDELAY RP VO = 3V 0.12F 6JA (160 - TA) (0.300 x VD) LP3982 www.ti.com SNVS185D – FEBRUARY 2002 – REVISED APRIL 2013 (6) Fault Detection The LP3982 provides a FAULT pin that goes low during out of regulation conditions like current limit and thermal shutdown, or when it approaches dropout. The latter monitors the input-to-output voltage differential and compares it against a threshold that is slightly above the dropout voltage. This threshold also tracks the dropout voltage as it varies with load current. Refer to Figure 4 in the typical characteristics section. The FAULT pin requires a pull-up resistor since it is an open-drain output. This resistor should be large in value to reduce energy drain. A 100 k Ω pull-up resistor works well for most applications. Figure 20 shows the LP3985 with delay added to the FAULT pin for the reset pin of a microprocessor. The output of the comparator stays low for a preset amount of time after the regulator comes out of a fault condition. Figure 20. Power on Delayed Reset Application The delay time for the application of Figure 20 is set as follows: (7) The application is set for a reset delay time of 8.8 ms. Note that the comparator should have high impedance inputs so as to not load down the VREF at the CC pin of the LP3982. Shutdown The LP3982 goes into sleep mode when the SHDN pin is in a logic low condition. During this condition, the pass transistor, error amplifier, and bandgap are turned off, reducing the supply current to 1 nA typical. The maximum voltage for a logic low at the SHDN pin is 0.4V. A minimum voltage of 2V at the SHDN pin will turn the LP3982 back on. The SHDN pin may be directly tied to VIN to keep the part on. The SHDN pin may exceed VIN but not the ABS MAX of 6.5V. Figure 21 shows an application that uses the SHDN pin. It detects when the battery is too low and disconnects the load by turning off the regulator. A micropower comparator (LMC7215) and reference (LM385) are combined with resistors to set the minimum battery voltage. At the minimum battery voltage, the comparator output goes low and tuns off the LP3982 and corresponding load. Hysteresis is added to the minimum battery threshold to prevent the battery's recovery voltage from falsely indicating an above minimum condition. When the load is disconnected from the battery, it automatically increases in terminal voltage because of the reduced IR drop across its internal resistance. The Minimum battery detector of Figure 21 has a low detection threshold (VLT) of 3.6V that corresponds to the minimum battery voltage. The upper threshold (VUT) is set for 4.6V in order to exceed the recovery voltage of the battery. Copyright © 2002–2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LP3982 |
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