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LM2660-MWC Scheda tecnica(PDF) 11 Page - Texas Instruments |
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LM2660-MWC Scheda tecnica(HTML) 11 Page - Texas Instruments |
11 / 27 page LM2660 www.ti.com SNVS135E – SEPTEMBER 1999 – REVISED DECEMBER 2014 9 Application and Implementation NOTE Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality. 9.1 Application Information The LM2660 CMOS charge-pump voltage converter is a versatile unregulated switched capacitor inverter or doubler. Operating from a wide 1.5 V to 5.5 V supply voltage, the LM2660 uses two low-cost capacitors to provide 100 mA of output current without the cost, size and EMI related to inductor-based converters. With an operating current of only 120 µA and operating efficiency greater than 90% at most loads, the LM2660 provides ideal performance for battery-powered systems. LM2660 devices can be operated directly in parallel to lower output impedance, thus providing more current at a given voltage. 9.2 Typical Applications 9.2.1 Voltage Inverter Figure 14. LM2660 Voltage Inverter 9.2.1.1 Design Requirements The main application of LM2660 is to generate a negative supply voltage. The voltage inverter circuit uses only two external capacitors as shown in the Figure 14. The range of the input supply voltage is 1.5 V to 5.5 V. For a supply voltage less than 3.5V, the LV pin must be connected to ground to bypass the internal regulator circuitry. This gives the best performance in low voltage applications. If the supply voltage is greater than 3.5 V, LV may be connected to ground or left open. The choice of leaving LV open simplifies the direct substitution of the LM2660 for the LMC7660 Switched Capacitor Voltage Converter. 9.2.1.2 Detailed Design Procedure The output characteristics of this circuit can be approximated by an ideal voltage source in series with a resistor. The voltage source equals −(V+). The output resistance Rout is a function of the ON resistance of the internal MOS switches, the oscillator frequency, and the capacitance and ESR of C1 and C2. A good approximation is: where • RSW is the sum of the ON resistance of the internal MOS switches shown in Figure 13. (1) High value, low ESR capacitors will reduce the output resistance. Instead of increasing the capacitance, the oscillator frequency can be increased to reduce the 2/(fosc × C1) term. Once this term is trivial compared with RSW and ESRs, further increasing in oscillator frequency and capacitance will become ineffective. The peak-to-peak output voltage ripple is determined by the oscillator frequency, and the capacitance and ESR of the output capacitor C2: (2) Again, using a low ESR capacitor will result in lower ripple. Copyright © 1999–2014, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LM2660 |
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