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NCP1239ED65R2G Datasheet(PDF) 15 Page - ON Semiconductor |
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NCP1239ED65R2G Datasheet(HTML) 15 Page - ON Semiconductor |
15 / 26 page NCP1239 www.onsemi.com 15 HV CURRENT SOURCE PIN The NCP1239 HV circuitry provides three features: • Start-Up Current Source to Charge the VCC Capacitor at Power On • Brown-Out Protection: when the HV Pin Voltage is below VBO(off) for the 68-ms Blanking Time (136 ms for G version), the NCP1239 Stops Operating and Recovers whenthe HV Pin Voltage Exceeds VBO(on) • Over Power Protection: HV Pin Voltage is Sensed to Determine the Amount of OPP Current Flowing Out the CS Pin The HV pin can be connected either to the bulk capacitor or to the input line terminals through a diode. It is further recommended to implement one or two resistors (in the range of 2.2 k W) to reduce the noise that can be picked-up by the HV pin. START-UP SEQUENCE The start-up time of a power supply largely depends on the time necessary to charge the VCC capacitor to the controller start-up threshold (VCC(on) which is 12 V typically). The NCP1239 high-voltage current-source provides the necessary current for a prompt start-up and turns off afterwards. The delivered current (ISTART1) is reduced to less than 0.5 mA when the VCC voltage is below VCC(inhibit) (1.2 V typically). This feature reduces the die stress if the VCC pin happens to be accidentally grounded. When VCC exceeds VCC(inhibit), a 3-mA current (ISTART2) is provided and charges the VCC capacitor. Please note that the internal IC consumption is increased from few mA to 310 mA (ICC4) when VCC crosses VCC(min) in order to have internal logic wake-up when VCC reaches VCC(on). The VCC charging time is then the total of the three following durations: • Charge from 0 V to VCC(inhibit): t START1 + V CC(inhibit) @ CV CC I START1 * ICC5 (eq. 1) • Charge from VCC(inhibit) to VCC(min): t START2 + V CC(min) * VCC(inhibit) @ CV CC I START2 * ICC5 (eq. 2) • Charge from VCC(min) to VCC(on): t START3 + V CC(on) * VCC(min) @ CV CC I START2 * ICC4 (eq. 3) Assuming a 22- mF VCC capacitor is selected and replacing ISTART1, ISTART2, ICC4, ICC5, VCC(inhibit) and VCC(on) by their typical values, it comes: t START1 + 12 @ 22 u 500 u * 20 u + 55 ms (eq. 4) t START2 + (10 * 1.2) @ 22 u 3m * 20 u + 65 ms (eq. 5) t START3 + (12 * 10) @ 22 u 3m * 310 u + 16 ms (eq. 6) t START + tSTART1 ) tSTART2 ) tSTART3 + 136 ms (eq. 7) Figure 32. The VCC at Start-Up is Made of Two Segments Given the Short-Circuit Protection Implemented on the HV Source t start1 t start2 t start3 v cc(t) V cc(on) V cc(inhibit) V cc(min) |
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