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TC7660COATR Fiches technique(PDF) 8 Page - Microchip Technology |
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TC7660COATR Fiches technique(HTML) 8 Page - Microchip Technology |
8 / 18 page TCM680 DS21486C-page 8 © 2005 Microchip Technology Inc. 5.0 APPLICATIONS INFORMATION 5.1 Voltage Multiplication and Inversion The TCM680 performs voltage multiplication and inver- sion simultaneously, providing positive and negative outputs (Figure 5-1). The magnitude of both outputs is, approximately, twice the input voltage. Unlike other switched capacitor converters, the TCM680 requires only four external capacitors to provide both functions simultaneously. FIGURE 5-1: Positive and Negative Converter. 5.2 Capacitor Selection The TCM680 requires only 4 external capacitors for operation, which can be inexpensive, polarized alumi- num electrolytic types. For the circuit in Figure 5-1, the output characteristics are largely determined by the external capacitors. An expression for ROUT can be derived as shown below: EQUATION Assuming all switch resistances are approximately equal: EQUATION ROUT is typically 140Ω at +25°C with VIN = +5V and C1 and C2 as 4.7 µF low ESR capacitors. The fixed term (32RSW) is about 130Ω. It can easily be seen 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 electrolytic capacitors. Table 5-1 shows ROUT for various values of C1 and C2 (assume 0.5Ω ESR). C1 and C4 must be rated at 6 VDC or greater while C2 and C3 must be rated at 12 VDC or greater. Output voltage ripple is affected by C3 and C4. Typically, the larger the value of C3 and C4, the less the ripple for a given load current. The formula for VRIPPLE(p-p) is given below: EQUATION For a 10 µF (0.5 Ω ESR) capacitor for C3, C4, fPUMP = 21 kHz and IOUT = 10 mA, the peak-to-peak ripple voltage at the output will be less than 100 mV. In most applications (IOUT ≤ 10 mA), 10-20 µF output capacitors and 1-5 µF pump capacitors will suffice. Table 5-2 shows VRIPPLE for different values of C3 and C4 (assume 1 Ω ESR). TABLE 5-1: OUTPUT RESISTANCE VS. C1, C2 TABLE 5-2: VRIPPLE PEAK-TO-PEAK VS. C3, C4 (IOUT 10 mA) GND GND TCM680 8 7 6 5 4 3 2 1 + + + VIN C1 + C2 + C1 - VOUT - VOUT + VOUT - VOUT + + VIN C1 22 µF C2 22 µF C4 22 µF C3 22 µF C2 - ROUT + =4(R SW1 +RSW2 +ESRC1 +RSW3 +RSW4 +ESRC2) +4(RSW1 +RSW2 +ESRC1 +RSW3 +RSW4 +ESRC2) +1/(fPUMP x C1) + 1/(fPUMP x C2) + ESRC4 ROUT – =4(R SW1 +RSW2 +ESRC1 +RSW3 +RSW4 +ESRC2) +4(RSW1 +RSW2 +ESRC1 +RSW3 +RSW4 +ESRC2) +1/(fPUMP x C1) + 1/(fPUMP x C2) + ESRC3 ROUT + = 32R SW + 8ESRC1 + 8ESRC2 + ESRC4 +1/(fPUMP x C1) + 1/(fPUMP x C2) ROUT – = 32R SW + 8ESRC1 + 8ESRC2 + ESRC3 +1/(fPUMP x C1) + 1/(fPUMP x C2) C1, C2 (µF) ROUT +, R OUT - (Ω) 0.1 1089 0.47 339 1232 3.3 165 4.7 157 10 146 22 141 100 137 C3, C4 (µF) VRIPPLE(p-p) +,V RIPPLE(p-p) - (mV) 0.47 1540 1734 3.3 236 4.7 172 10 91 22 52 100 27 VRIPPLE(p-p) + ={1/[2(f PUMP /3) x C4] + 2(ESRC4)} (IOUT +) VRIPPLE(p-p) – ={1/[2(f PUMP /3) x C3] + 2(ESRC3)} (IOUT –) |
Numéro de pièce similaire - TC7660COATR |
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Description similaire - TC7660COATR |
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