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TL7660CDGKR датащи(PDF) 9 Page - Texas Instruments |
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TL7660CDGKR датащи(HTML) 9 Page - Texas Instruments |
9 / 19 page www.ti.com Typical Applications Simple Negative Voltage Converter 1 2 3 4 8 7 6 5 + TL7660 + - - 10 µF V+ 10 µF V = –V+ OUT TL7660 CMOS VOLTAGE CONVERTER SCAS794 – JUNE 2006 APPLICATION INFORMATION (continued) The majority of applications will undoubtedly utilize the TL7660 for generation of negative supply voltages. Figure 3 shows typical connections to provide a negative supply negative (GND) for supply voltages below 3.5 V. Figure 3. Simple Negative-Voltage Converter The output characteristics of the circuit in Figure 3 can be approximated by an ideal voltage source in series with a resistance. The voltage source has a value of –VCC. The output impedance (RO) is a function of the ON resistance of the internal MOS switches (shown in Figure 2), the switching frequency, the value of C1 and C2, and the ESR (equivalent series resistance) of C1 and C2. A good first order approximation for RO is: RO ≈ 2(RSW1 + RSW3 + ESRC1) + 2(RSW2 + RSW4 + ESRC1) RO ≈ 2(RSW1 + RSW3 + ESRC1) + 1/fPUMPC1 + ESRC2 Where fPUMP = fOSC/2 , RSWX = MOSFET switch resistance. Combining the four RSWX terms as RSW, we see that: RO ≈ 2 (RSW) + 1/fPUMPC1 + 4 (ESRC1) + ESRC2 RSW, the total switch resistance, is a function of supply voltage and temperature (See the Output Source Resistance graphs). Careful selection of C1 and C2 reduces the remaining terms, minimizing the output impedance. High value capacitors reduce the 1/fPUMPC1 component, and low ESR capacitors lower the ESR term. Increasing the oscillator frequency reduces the 1/fPUMPC1 term but may have the side effect of a net increase in output impedance when C1 > 10 µF and there is no longer enough time to fully charge the capacitors every cycle. In a typical application where fOSC = 10 kHz and C = C1 = C2 = 10 µF: RO ≈ 2(23) + 1/(5 × 10 3)(10–5) + 4(ESR C1) + ESRC2 RO ≈ 46 + 20 + 5 (ESRC) Because the ESRs of the capacitors are reflected in the output impedance multiplied by a factor of 5, a high value could potentially swamp out a low 1/fPUMPC1 term, rendering an increase in switching frequency or filter capacitance ineffective. Typical electrolytic capacitors may have ESRs as high as 10 Ω. 9 Submit Documentation Feedback |
Аналогичный номер детали - TL7660CDGKR |
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Аналогичное описание - TL7660CDGKR |
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