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UBA2211BT Datasheet(PDF) 7 Page - NXP Semiconductors |
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UBA2211BT Datasheet(HTML) 7 Page - NXP Semiconductors |
7 / 20 page UBA2211 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved. Product data sheet Rev. 3 — 26 August 2011 7 of 20 NXP Semiconductors UBA2211 Half-bridge power IC family for CFL lamps (3) If during the preheat time, capacitive mode is sensed and the internal VSW HIGH node is discharged. The frequency sweep restarts at fmax which is equal to 2.5 fmin. 7.6 Ignition state The ignition state is entered after the preheat state has finished. The current ISW charges the capacitor on pin SW (CSW) up to 0.6 VH(RC) which corresponds to the frequency fosc(nom). During this frequency sweep, the resonance frequency is reached resulting in the ignition of the lamp (see Figure 4). The combination of lamp inductor (Llamp) and lamp capacitor (Clamp) set the resonance frequency. The ignition state ends when the voltage on pin SW (VSW) reaches 0.6 VH(RC). 7.7 Steady state In the steady state, the RMS current control is active. This control sets the frequency so that the RMS voltage across the sense resistor (RSENSE) is equal to VO(ref)RMS. This ensures the current through the power switches and through the lamp is constant. This results in constant IC dissipation and temperature at a fixed ambient temperature. During one oscillator clock cycle, the voltage on pin SENSE (VSENSE) is squared and converted into a positive current. This discharge current is added to the capacitor CSW. Fig 5. Vlamp, fosc(int), VSW and VSW(ph) plotted against time C sw t ph 1.5 s 100 nF ------------------------------------ = preheat time ignition 2.5 × fosc(nom) 001aal992 RMS control fosc(nom) fosc(int) VSW HIGH 0.6 × VH(RC) 0 VSW(ph) time (s) VSW Vlamp VSW |
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