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LM2775 Arkusz danych(PDF) 9 Page - Texas Instruments |
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LM2775 Arkusz danych(HTML) 9 Page - Texas Instruments |
9 / 27 page 12 11 12 11 S2 S4 S1 S3 1.2-V Ref. 2-MHz Osc. OCL OCL = Current Limit VIN VOUT C1- C1+ EN LM2775 GND PFM EN PFM OUTDIS LM2775 www.ti.com SNVSA57 – MAY 2015 7 Detailed Description 7.1 Overview The LM2775 is a regulated switched capacitor doubler that, by combining the principles of switched-capacitor voltage boost and linear regulation, generates a regulated output from an extended Li-Ion input voltage range. A two-phase non-overlapping clock generated internally controls the operation of the doubler. During the charge phase ( φ1), the flying capacitor (C1) is connected between the input and ground through internal pass transistor switches and is charged to the input voltage. In the pump phase that follows ( φ2), the flying capacitor is connected between the input and output through similar switches. Stacked atop the input, the charge of the flying capacitor boosts the output voltage and supplies the load current. A traditional switched capacitor doubler operating in this manner uses switches with very low on-resistance to generate an output voltage that is 2× the input voltage. Regulation is achieved by modulating the current of the two switches connected to the VIN pin (one switch in each phase). 7.2 Functional Block Diagram 7.3 Feature Description 7.3.1 Pre-Regulation The very low input current ripple of the LM2775, resulting from internal pre-regulation, adds minimal noise to the input line. The core of the LM2775 is very similar to that of a basic switched capacitor doubler: it is composed of four switches and a flying capacitor (external). Regulation is achieved by controlling the current through the two switches connected to the VIN pin (one switch in each phase). The regulation is done before the voltage doubling, giving rise to the term "pre-regulation". It is pre-regulation that eliminates most of the input current ripple that is a typical and undesirable characteristic of a many switched capacitor converters. 7.3.2 Input Current Limit The LM2775 contains current limit circuitry that protects the device in the event of excessive input current and/or output shorts to ground. The input current is limited to 600 mA (typical) when the output is shorted directly to ground. When the LM2775 is current limiting, power dissipation in the device is likely to be quite high. In this event, thermal cycling should be expected. Copyright © 2015, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM2775 |
Podobny numer części - LM2775_15 |
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Podobny opis - LM2775_15 |
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