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TC7660IJA 데이터시트(PDF) 6 Page - Microchip Technology |
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TC7660IJA 데이터시트(HTML) 6 Page - Microchip Technology |
6 / 20 page TC7660 DS21465C-page 6 2002-2011 Microchip Technology Inc. 4.0 DETAILED DESCRIPTION 4.1 Theory of Operation The TC7660 charge pump converter inverts the voltage applied to the V+ pin. The conversion consists of a two- phase operation (Figure 4-1). During the first phase, switches S2 and S4 are open and switches S1 and S3 are closed. C1 charges to the voltage applied to the V+ pin, with the load current being supplied from C2. Dur- ing the second phase, switches S2 and S4 are closed and switches S1 and S3 are open. Charge is trans- ferred from C1 to C2, with the load current being supplied from C1. FIGURE 4-1: Ideal Switched Capacitor Inverter. In this manner, the TC7660 performs a voltage inver- sion, but does not provide regulation. The average out- put voltage will drop in a linear manner with respect to load current. The equivalent circuit of the charge pump inverter can be modeled as an ideal voltage source in series with a resistor, as shown in Figure 4-2. FIGURE 4-2: Switched Capacitor Inverter Equivalent Circuit Model. The value of the series resistor (ROUT) is a function of the switching frequency, capacitance and equivalent series resistance (ESR) of C1 and C2 and the on-resis- tance of switches S1, S2, S3 and S4. A close approximation for ROUT is given in the following equation: EQUATION 4.2 Switched Capacitor Inverter Power Losses The overall power loss of a switched capacitor inverter is affected by four factors: 1. Losses from power consumed by the internal oscillator, switch drive, etc. These losses will vary with input voltage, temperature and oscillator frequency. 2. Conduction losses in the non-ideal switches. 3. Losses due to the non-ideal nature of the external capacitors. 4. Losses that occur during charge transfer from C1 to C2 when a voltage difference between the capacitors exists. Figure 4-3 depicts the non-ideal elements associated with the switched capacitor inverter power loss. FIGURE 4-3: Non-Ideal Switched Capacitor Inverter. The power loss is calculated using the following equation: EQUATION V+ GND S 3 S1 S2 S4 C2 VOUT = -VIN C1 + + - + ROUT VOUT V+ ROUT 1 fPUMP C1 ----------------------------- 8RSW 4ESRC1 ESRC2 ++ + = RSW on-resistance of the switches = ESRC1 equivalent series resistance of C1 = ESRC2 equivalent series resistance of C2 = fPUMP fOSC 2 ----------- = Where: LOAD C1 C2 RSW S1 IDD ESRC1 V+ + - RSW S2 RSW S3 RSW S4 ESRC2 IOUT ++ PLOSS IOUT 2 ROUT IDD V + + = |
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