Datasheet NCP1729 (ON Semiconductor) - 5
| Manufacturer | ON Semiconductor |
| Description | Switched Capacitor Voltage Inverter |
| Pages / Page | 22 / 5 — NCP1729. Charge Pump Efficiency. Figure 14. Test Setup/Voltage Inverter. … |
| File Format / Size | PDF / 181 Kb |
| Document Language | English |
NCP1729. Charge Pump Efficiency. Figure 14. Test Setup/Voltage Inverter. DETAILED OPERATING DESCRIPTION
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NCP1729
−Vout
Charge Pump Efficiency
The overall power conversion efficiency of the charge pump is affected by four factors: C RL 2 1 6 + 1. Losses from power consumed by the internal OSC oscillator, switch drive, etc. (which vary with input voltage, temperature and oscillator frequency). + V 2 in 5 2. I2R losses due to the on−resistance of the MOSFET + C1 C3 switches on−board the charge pump. 3. Charge pump capacitor losses due to 3 4 Equivalent Series Resistance (ESR). 4. Losses that occur during charge transfer from the commutation capacitor to the output capacitor when C1 = C2 = C3 = 3.3 F a voltage difference between the two capacitors
Figure 14. Test Setup/Voltage Inverter
exists. Most of the conversion losses are due to factors 2, 3 and 4. These losses are given by Equation 1.
DETAILED OPERATING DESCRIPTION
P I 2 R I 2 The NCP1729 charge pump converter inverts the voltage LOSS(2,3,4) out out out applied to the Vin pin. Conversion consists of a two−phase 1 operation (Figure 15). During the first phase, switches S 8R 4ESR ESR 2 (f )C SWITCH C C OSC 1 1 2 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 (eq. 1) from C2. During the second phase, S2 and S4 are closed, and The 1/(fOSC)(C1) term in Equation 1 is the effective output S1 and S3 are open. This action connects C1 across C2, resistance of an ideal switched capacitor circuit (Figures 16 restoring charge to C2. and 17). The losses due to charge transfer above are also shown in S1 S2 Equation 2. The output voltage ripple is given by Equation 3. Vin P 2 2 LOSS [ 0.5C 1 (Vin Vout ) C1 0.5C 2 2 (VRIPPLE 2VoutVRIPPLE)] fOSC (eq. 2) C2 Iout V 2(Iout)(ESR ) S3 S4 RIPPLE (f )(C ) C OSC 2 2 −V (eq. 3) out From OSC f Vin Vout
Figure 15. Ideal Switched Capacitor Charge Pump
RL C C 1 2
APPLICATIONS INFORMATION Output Voltage Considerations Figure 16. Ideal Switched Capacitor Model
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 REQUIV equivalent output resistance is approximately 26 nominal Vin Vout at 25°C with Vin = 5.0 V. Vout is approximately −5.0 V at light loads, and drops according to the equation below: R 1 R EQUIV L f C1 C2 VDROP Iout Rout Vout (Vin VDROP)
Figure 17. Equivalent Output Resistance http://onsemi.com 5
NCP1729
−Vout
Charge Pump Efficiency
The overall power conversion efficiency of the charge pump is affected by four factors: C RL 2 1 6 + 1. Losses from power consumed by the internal OSC oscillator, switch drive, etc. (which vary with input voltage, temperature and oscillator frequency). + V 2 in 5 2. I2R losses due to the on−resistance of the MOSFET + C1 C3 switches on−board the charge pump. 3. Charge pump capacitor losses due to 3 4 Equivalent Series Resistance (ESR). 4. Losses that occur during charge transfer from the commutation capacitor to the output capacitor when C1 = C2 = C3 = 3.3 F a voltage difference between the two capacitors
Figure 14. Test Setup/Voltage Inverter
exists. Most of the conversion losses are due to factors 2, 3 and 4. These losses are given by Equation 1.
DETAILED OPERATING DESCRIPTION
P I 2 R I 2 The NCP1729 charge pump converter inverts the voltage LOSS(2,3,4) out out out applied to the Vin pin. Conversion consists of a two−phase 1 operation (Figure 15). During the first phase, switches S 8R 4ESR ESR 2 (f )C SWITCH C C OSC 1 1 2 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 (eq. 1) from C2. During the second phase, S2 and S4 are closed, and The 1/(fOSC)(C1) term in Equation 1 is the effective output S1 and S3 are open. This action connects C1 across C2, resistance of an ideal switched capacitor circuit (Figures 16 restoring charge to C2. and 17). The losses due to charge transfer above are also shown in S1 S2 Equation 2. The output voltage ripple is given by Equation 3. Vin P 2 2 LOSS [ 0.5C 1 (Vin Vout ) C1 0.5C 2 2 (VRIPPLE 2VoutVRIPPLE)] fOSC (eq. 2) C2 Iout V 2(Iout)(ESR ) S3 S4 RIPPLE (f )(C ) C OSC 2 2 −V (eq. 3) out From OSC f Vin Vout
Figure 15. Ideal Switched Capacitor Charge Pump
RL C C 1 2
APPLICATIONS INFORMATION Output Voltage Considerations Figure 16. Ideal Switched Capacitor Model
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 REQUIV equivalent output resistance is approximately 26 nominal Vin Vout at 25°C with Vin = 5.0 V. Vout is approximately −5.0 V at light loads, and drops according to the equation below: R 1 R EQUIV L f C1 C2 VDROP Iout Rout Vout (Vin VDROP)
Figure 17. Equivalent Output Resistance http://onsemi.com 5
