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FAN7532MX Datasheet(PDF) 10 Page - Fairchild Semiconductor |
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FAN7532MX Datasheet(HTML) 10 Page - Fairchild Semiconductor |
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10 / 16 page  © 2006 Fairchild Semiconductor Corporation www.fairchildsemi.com FAN7532 Rev. 1.0.2 10 4. Preheating Mode The preheating mode is defined as the IC’s internal status when the VCPH is between 0V and 2.9V. During preheating, the current that flows through the ballast circuit heats the lamp filaments. This is necessary for maximizing lamp life and reducing the required ignition voltage. When the VCC exceeds the UVLO high threshold, the preheating time set-up capacitor, CPH, starts being charged by the internal 1.5µA current source until the VCPH reaches 2.9V. Until the VCPH reaches 2.9V, the switching frequency throughout the preheating mode is determined by CT and RPH. The preheating time is determined by the CPH and the 1.5µA current source. Therefore, the preheating time is determined by equation (3): The preheating frequency is determined by the amount of charging and discharging current to the CT capacitor. The charging and discharging current during preheating mode is decided by equation (4): The charging and discharging time of the CT capacitor during preheating mode is decided by equation (5): Finally, the FAN7532’s preheating frequency in the preheating period is determined by equation (6): 5. Ignition Mode The ignition mode is defined as the IC’s internal status when VCPH is approximately between 2.9V and 5V. During ignition, the operating frequency is decreased to a pre-determined value. At the same time, a very high- voltage for igniting the lamp is established across the lamp. When the VCPH exceeds 2.9V, the FAN7532 enters the ignition mode. Once VCPH exceeds 5V, the device enters the run mode described in the following section. In the ignition period, the internal 10mA current source charges the external preheating timing capacitor (CPH) to increase noise immunity with the sharp slope of the VCPH. The ignition time is determined by the CPH and internal 10mA current source ( ). In this mode, the switching frequency is determined by CT, RPH, and RT. Therefore, the charging and discharging currents change according to VCPH and are determined by equation (7). 6. Run Mode After the lamp has successfully ignited, the FAN7532 enters run mode. The run mode is defined as the IC’s internal status when VCPH is higher than 5V. In this mode, the lamp is being driven with a normal power level after the lamp is discharged. The run mode switching frequency is determined by the timing resistor RT and the timing capacitor CT. When the VCPH exceeds 5V, the protection-masking mode is disabled and the IC can enter the protection mode. The running frequency is determined by the amount of charging and discharging current to CT capacitor. The charging and discharging currents during preheating mode are decided by the equation (8): Finally, the preheating frequency in the preheating period using the FAN7532 is determined by the equation (10): CPH V V V ;Preheating Frequency 02.9 , ≤≤ () () PH RT CT RT PH CPH II II V V I VV V V V ;Ignition Frequency 52.9 52.9 2.9 5 , − =+ − = − ≤≤ () () PH RT CT RT CPH CPH CT RT II II V V VV VV I I ;Run Frequency 5 52.9 5 , − =+ − − ≥ = CPH pre charging V tCPH I =× (3) (4) () () ref pre ch PH ref pre disch PH V I R V I Vref V Constant R _ _ 4 6.25 4, 4 =× × =× = (5) CT pre ch T pre ch CT pre disch T pre disch dV tC I dV t C dVCT=3.45V (Constant) I _ _ _ _ , =× =× () pre pre ch pre disch f tt __ 1 2 = ×+ (6) CPH ign PH CPH V TC I Δ Δ= × () () PH RT CT RT CPH II II V V VV 5 52.9 − =+ − − (7) () ref run ch T ref run disch T V I R V I Vref=4V (Constant) R _ _ 2 6.25 2, =× × =× (8) CT run ch T run ch CT run disch T run disch dV tC I dV t C dVCT=3.45V (Constant) I _ _ _ _ , =× =× (9) () run run ch run disch f tt __ 1 2 = ×+ (10) |
Similar Part No. - FAN7532MX |
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Similar Description - FAN7532MX |
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