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IRS2166D Datasheet(PDF) 9 Page - International Rectifier |
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IRS2166D Datasheet(HTML) 9 Page - International Rectifier |
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9 / 18 page  IRS2166D(S)PbF www.irf.com Page 9 I. Ballast Section Functional Description Undervoltage Lock-Out Mode (UVLO) The undervoltage lock-out mode (UVLO) is defined as the state the IC is in when VCC is below the turn-on threshold of the IC. To identify the different modes of the IC, refer to the State Diagram shown on page 7 of this document. The IRS2166D undervoltage lock-out is designed to maintain an ultra low supply current of 250 µA (IQCCUV), and to guarantee the IC is fully functional before the high and low side output drivers are activated. Fig. 1 shows an efficient supply voltage using the start-up current of the IRS2166D together with a charge pump from the ballast output stage (RSUPPLY, CVCC, DCP1, and DCP2). LO COM VB VS HO V BUS(+) V BUS(-) VCC D BOOT C BOOT 16 15 14 13 12 11 M2 M1 C VCC R SUPPLY D CP1 D CP2 Half-Bridge Output R CS C SNUB Fig. 1: Start-up and supply circuitry The start-up capacitor (CVCC) is charged by current through supply resistor (RSUPPLY) minus the start-up current drawn by the IC. This resistor is chosen to set the line input voltage turn-on threshold for the ballast. Once the capacitor voltage on VCC reaches the start-up threshold VCCUV+, and the SD pin is below 3.0 V (VSDTH-), the IC turns on and HO and LO begin to oscillate. The capacitor begins to discharge due to the increase in IC operating current (Fig. 2). During the discharge cycle, the rectified current from the charge pump charges the capacitor above the IC turn-off threshold. The charge pump and the internal 15.6 V (VCLAMP) zener clamp of the IC take over as the supply voltage. The start-up capacitor and snubber capacitor must be selected such that enough supply current is available over all ballast operating conditions. A supply capacitor (CBOOT) comprises the supply voltage for the high side driver circuitry. To guarantee that the high-side supply is charged up before the first pulse on pin HO, the first pulse from the output drivers comes from the LO pin. During undervoltage lock-out mode, the high- and low-side driver outputs HO and LO are both low, pin CT is connected internally to COM to disable the oscillator, and pin CPH is connected internally to COM for resetting the preheat time. DISCHARGE TIME INTERNAL VCC ZENER CLAMP VOLTAGE VHYST V UVLO+ V UVLO- CHARGE PUMP OUTPUT t V C1 R SUPPLY & CVCC TIME CONSTANT C VCC DISCHARGE Fig. 2: Supply capacitor (CVCC) voltage Preheat Mode (PH) The preheat mode is defined as the state the IC is in when the lamp filaments are being heated to their correct emission temperature. This is necessary for maximizing lamp life and reducing the required ignition voltage. The IRS2166D enters preheat mode when V CC exceeds the UVLO positive-going threshold V CCUV +. HO and LO begin to oscillate at the preheat frequency with 50% duty cycle and with a deadtime which is set by the value of the external timing capacitor, CT, and internal deadtime resistor, RDT. Pin CPH is disconnected from COM and an internal 3.6 µA (ICPH) current source (Fig. 3) charges the external preheat timing capacitor on CPH linearly. The over-current protection on pin CS is enabled during preheat. The preheat frequency is determined by the parallel combination of resistors RT and RPH, together with timing capacitor CT. CT charges and discharges between 1/3 (VCT-) and 3/5 (VCT+) of VCC (see Timing Diagram, page 9). CT is charged exponentially through the parallel combination of RT and RPH connected internally to VCC through MOSFET S1. The charge time of CT from 1/3 to 3/5 VCC is the on-time of the respective output gate driver, HO or LO. Once CT exceeds 3/5 VCC, MOSFET S1 is turned off, disconnecting RT and RPH from VCC. CT is then discharged exponentially through an internal resistor, RDT, through MOSFET S3 to COM. The discharge time of CT from 3/5 to 1/3 VCC is the deadtime (both off) of the output gate drivers, HO and LO. The selected value of CT and RDT program the desired deadtime (see Design Equations, page 15, Equations 1 and 2). Once CT discharges below 1/3 VCC, MOSFET S3 is turned off, disconnecting RDT from COM, and MOSFET S1 is turned on, connecting RT and RPH again to VCC. The frequency remains at the preheat frequency until the voltage on pin CPH exceeds 10 V and the IC enters ignition mode. During the preheat mode, both the over- current protection and the DC bus undervoltage reset are enabled when pin CPH exceeds 12 V (VCPHRUN). Ignition Mode (IGN) The ignition mode is defined as the state the IC is in when a high voltage is being established across the lamp necessary for igniting the lamp. The IRS2166D enters ignition mode when the voltage on pin CPH exceeds 10.8 V (VCPHEOP). Pin CPH is connected internally to the |
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