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LP8345IDT-5.0 Datasheet(PDF) 10 Page - National Semiconductor (TI) |
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LP8345IDT-5.0 Datasheet(HTML) 10 Page - National Semiconductor (TI) |
10 / 13 page Applications Section GENERAL INFORMATION The LP8345 is a low-dropout, low quiescent current linear regulator. As shown in Figure 1 it consists of a 1.25V refer- ence, error amplifier, MOSFET driver, PMOS pass transistor and for the fixed output versions, an internal feedback net- work (R 1/R2). In addition, the device is protected from over- load by a thermal shutdown circuit and a foldback current limit circuit. The 1.25V reference is connected to the inverting input of the error amplifier. Regulation of the output voltage is achieved by means of negative feedback to the non- inverting input of the error amplifier. Feedback resistors R 1 and R 2 are either internal or external to the device, depend- ing on whether it is a fixed voltage version or the adjustable version. The negative feedback and high open loop gain of the error amplifier cause the two inputs of the error amp to be virtually equal in voltage. If the output voltage changes due to load changes, the error amplifier and MOSFET driver provide the appropriate drive to the pass transistor to main- tain the error amplifier’s inputs as virtually equal. EXTERNAL CAPACITOR An Input capacitor of 1µF or greater is required between the LP8345 V IN pin and ground. While 1µF will provide adequate bypassing of the V IN supply larger values of input capacitor (i.e. 10µF) can provide improved bypassing of power supply noise. Stable operation can be achieved with an output capacitor of 1µF or greater, either ceramic X7R dielectric or aluminum/ tantalum electrolytic. While the minimum capacitor value is 1µF, the typical output capacitor values selected range from 1µF to 10µF. The larger values provide improved load- transient response, power supply rejection and stability. OUTPUT VOLTAGE SETTING (ADJ VERSION ONLY) The output voltage is set according to the amount of nega- tive feedback (Note that the pass transistor inverts the feed- back signal). This feedback is determined by R 1 and R2 with the resulting output voltage represented by the following equation: Use the following equation to determine the values of R 1 and R 2 for a desired VOUT (R2 = 100 Ω is recommended). MINIMUM LOAD CURRENT A minimum load of 100µA is required for regulation and stability over the entire operating temperature range. If ac- tual load current fall below 100µA it is recommended that a resistor of value R L =VO/100µA be placed between VO and ground. 20064803 FIGURE 1. LP8345 Functional Block Diagram www.national.com 10 |
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