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UP2B-681 Datasheet(PDF) 6 Page - ON Semiconductor |
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UP2B-681 Datasheet(HTML) 6 Page - ON Semiconductor |
6 / 10 page AND8098/D http://onsemi.com 6 The proposed buck-boost is better in term of the standby ability. It is because the VCC charging current in Figure 2(b) only passes through the inductor. The charging current pulses become an averaged energy stored in the inductor and consume smaller amount of power comparing to the buck case. Figure 7. Auxiliary Winding to improve standby Abillity (a) Buck (b) Buck-boost The auxiliary winding to supply the VCC voltage in Figure 7 is a method to improve the standby ability. The auxiliary winding keeps the VCC voltage above 7.5 V and disable the VCC charging current and hence its standby loss. The auxiliary winding is coupled from the inductor L with polarity same as the regulated output voltage. The VCC voltage in the auxiliary winding is designed to be between the normal VCC limits of 7.5 and 8.5 V typically. The frequency jittering feature loses when the VCC voltage is fixed. When output is shorted, there will be no voltage coming from the auxiliary winding and the circuit will enter fault mode with the 4.5 V-8.5 V-7.5 V-4.5 V hysteresis loop. Another method to supply the VCC voltage is coupling capacitor technique in Figure 8. The output voltage is coupled to the inserted capacitor when the diodes are closed. The voltage drop of the diodes compensate each other. Hence, the diode voltage drop effect can be neglected. The NCP1052 needs a nominal VCC voltage of 8V. The inserted resistor consumes some voltage from the output voltage Vout to make a 8V to the VCC pin. Based on the 0.5mA typical current consumption of VCC pin. The inserted resistance value is (Vout - 8) / 0.5 k W. Figure 8. Coupling Capacitor Technique to Improve Standby Abillity (a) Buck (b) Buck-boost Temperature Rise The NCP1052 is a very compact package with the control circuit and high-voltage power switch. Its typical on resistance is 22 Ω. Temperature rise exists. It is recommended to design the PCB board with a large copper area next to the device as a heatsink. This heatsink decreases |
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