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TC682COA Fiches technique(PDF) 5 Page - Microchip Technology |
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TC682COA Fiches technique(HTML) 5 Page - Microchip Technology |
5 / 14 page © 2006 Microchip Technology Inc. DS21453C-page 5 TC682 4.0 TYPICAL APPLICATIONS 4.1 Negative Doubling Converter The most common application of the TC682 is as a charge pump voltage converter which provides a negative output of two times a positive input voltage (Figure 4-1). FIGURE 4-1: Inverting Voltage Doubler 4.2 Capacitor Selection The output resistance of the TC682 is determined, in part, by the ESR of the capacitors used. An expression for ROUT is derived as shown below: Assuming all switch resistances are approximately equal: ROUT is typically 140Ω at +25°C with VIN = +5V and 3.3 μF low ESR capacitors. The fixed term (16RSW) is about 80-90 Ω. It can be seen easily that increasing or decreasing values of C1 and C2 will affect efficiency by changing ROUT. However, be careful about ESR. This term can quickly become dominant with large electro- lytic capacitors. Table 4-1 shows ROUT for various values of C1 and C2 (assume 0.5 Ω ESR). C1 must be rated at 6VDC or greater while C2 and C3 must be rated at 12VDC or greater. Output voltage ripple is affected by C3. Typically the larger the value of C3 the less the ripple for a given load current. The formula for P-P VRIPPLE is given below: VRIPPLE = {1/[2(fPUMP x C3)] + 2(ESRC3)} (IOUT) For a 10 μF (0.5Ω ESR) capacitor for C3, fPUMP = 10 kHz and IOUT = 10 mA the peak-to-peak ripple voltage at the output will be less then 60 mV. In most applications (IOUT < = 10 mA) a 10-20 μF capacitor and 1-5 μF pump capacitors will suffice. Table 4-2 shows VRIPPLE for different values of C3 (assume 1Ω ESR). TABLE 4-1: OUTPUT RESISTANCE VS. C1, C2 TABLE 4-2: VRIPPLE PEAK-TO-PEAK VS. C3 (IOUT 10mA) GND GND TC682 22 μF 22 μF 22 μF 7 6 5 4 3 2 1 + VIN C1+ C2+ C1– C2– V–OUT C1 C2 V–OUT + + VIN C3 ROUT =2(RSW1 +RSW2 +ESRC1 +RSW3 +RSW4 +ESRC2) +2(RSW1 +RSW2 +ESRC1 +RSW3 +RSW4 +ESRC2) +1/(fPUMP x C1) +1/(fPUMP x C2) +ESRC3 ROUT = 16RSW + 4ESRC1 + 4ESRC2 + ESRC3 +1/(fPUMP x C1) +1/(fPUMP x C2) C1, C2 ( μF) ROUT(Ω) 0.05 4085 0.10 2084 0.47 510 1.00 285 3.30 145 5.00 125 10.00 105 22.00 94 100.00 87 C3 ( μF) VRIPPLE (mV) 0.50 1020 1.00 520 3.30 172 5.00 120 10.00 70 22.00 43 100.00 25 |
Numéro de pièce similaire - TC682COA |
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Description similaire - TC682COA |
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