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NCP1729 Datasheet(PDF) 5 Page - ON Semiconductor |
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NCP1729 Datasheet(HTML) 5 Page - ON Semiconductor |
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5 / 22 page  NCP1729 http://onsemi.com 5 6 4 2 3 1 OSC −Vout C1 C2 RL + + C3 Vin + Figure 14. Test Setup/Voltage Inverter 5 C1 = C2 = C3 = 3.3 mF DETAILED OPERATING DESCRIPTION The NCP1729 charge pump converter inverts the voltage applied to the Vin pin. Conversion consists of a two−phase operation (Figure 15). During the first phase, switches S2 and S4 are open and S1 and S3 are closed. During this time, C1 charges to the voltage on Vin and load current is supplied from C2. During the second phase, S2 and S4 are closed, and S1 and S3 are open. This action connects C1 across C2, restoring charge to C2. Figure 15. Ideal Switched Capacitor Charge Pump S3 S4 C2 C1 S1 S2 Vin −Vout From OSC APPLICATIONS INFORMATION Output Voltage Considerations The NCP1729 performs voltage conversion but does not provide regulation. The output voltage will drop in a linear manner with respect to load current. The value of this equivalent output resistance is approximately 26 W nominal at 25 °C with Vin = 5.0 V. Vout is approximately −5.0 V at light loads, and drops according to the equation below: VDROP + Iout Rout Vout + * (Vin * VDROP) Charge Pump Efficiency The overall power conversion efficiency of the charge pump is affected by four factors: 1. Losses from power consumed by the internal oscillator, switch drive, etc. (which vary with input voltage, temperature and oscillator frequency). 2. I2R losses due to the on−resistance of the MOSFET switches on−board the charge pump. 3. Charge pump capacitor losses due to Equivalent Series Resistance (ESR). 4. Losses that occur during charge transfer from the commutation capacitor to the output capacitor when a voltage difference between the two capacitors exists. Most of the conversion losses are due to factors 2, 3 and 4. These losses are given by Equation 1. P LOSS(2,3,4) + Iout 2 Rout ^ Iout 2 1 (f OSC )C1 ) 8R SWITCH ) 4ESR C1 ) ESR C2 (eq. 1) The 1/(fOSC)(C1) term in Equation 1 is the effective output resistance of an ideal switched capacitor circuit (Figures 16 and 17). The losses due to charge transfer above are also shown in Equation 2. The output voltage ripple is given by Equation 3. ) 0.5C2 (VRIPPLE2 * 2VoutVRIPPLE)] fOSC PLOSS + [0.5C1 (Vin 2 * Vout2) (eq. 2) V RIPPLE + Iout (f OSC )(C 2 ) ) 2(I out)(ESRC2 ) (eq. 3) RL C2 C1 Vin Vout f Figure 16. Ideal Switched Capacitor Model RL C2 Vin Vout REQUIV R EQUIV + 1 f C1 Figure 17. Equivalent Output Resistance |
Similar Part No. - NCP1729_06 |
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Similar Description - NCP1729_06 |
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