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TC1240ECH データシート(PDF) 8 Page - Microchip Technology |
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TC1240ECH データシート(HTML) 8 Page - Microchip Technology |
8 / 18 page TC1240/TC1240A DS21516D-page 8 2001-2012 Microchip Technology Inc. The switching frequency in Equation 5-1b is defined as one-half the oscillator frequency (i.e., FSW = FOSC/2). The 1/(FSW)(C1) term in Equation 5-1b is the effective output resistance of an ideal switched capacitor circuit (Figure 5-1 and Figure 5-2). The output voltage ripple is given by Equation 5-2. EQUATION 5-2: FIGURE 5-1: Ideal Switched Capacitor Model. FIGURE 5-2: Equivalent Output Resistance. 5.3 Capacitor Selection In order to maintain the lowest output resistance and output ripple voltage, it is recommended that low ESR capacitors be used. Additionally, larger values of C1 will lower the output resistance and larger values of C2 will reduce output ripple (see Equation 5-1b). Table 5-1 shows various values of C1 and the corresponding output resistance values @ +25°C. It assumes a 0.1 ESR C1 and 0.9 RSW. Table 5-2 shows the output voltage ripple for various values of C2. The VRIPPLE values assume 5mA output load current and 0.1 ESR C2. TABLE 5-1: OUTPUT RESISTANCE VS. C1 (ESR = 0.1) TABLE 5-2: OUTPUT VOLTAGE RIPPLE VS. C2 (ESR = 0.1) IOUT 5mA V RIPPLE I OUT 2F SW C 2 -------------------------------- 2I OUT ESR C2 + = V+ VOUT RL C2 C1 f FSW x C1 1 V+ VOUT REQUIV REQUIV = RL C2 C1 (µF) TC1240 ROUT() TC1240A ROUT() 0.47 47 35 128.5 20.5 2.2 19.5 14 3.3 17 12 4.7 15.5 10.5 10 13.6 9.3 47 12.5 8.3 100 12.2 8.1 C1 (µF) TC1240/TC1240A VRIPPLE (mV) 0.47 142 167 2.2 30 3.3 20 4.7 14 10 6.7 47 2.5 100 1.6 |
同様の部品番号 - TC1240ECH |
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同様の説明 - TC1240ECH |
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