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FAN7530 데이터시트(PDF) 22 Page - Fairchild Semiconductor |
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FAN7530 데이터시트(HTML) 22 Page - Fairchild Semiconductor |
22 / 37 page © 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com FAN9611 / FAN9612 • Rev. 1.1.3 22 Quick Setup Guide The FAN9611/12 can be configured following the next steps outlined in this section. This Quick Setup Guide refers to the schematic diagram and component references of Figure 33. It uses the equations derived and explained in Application Note AN-6086. In preparation to calculate the setup component values, the power supply specification must be known. Furthermore, a few power stage components must be pre-calculated before the controller design begins as their values determine the component selections. An Excel design tool is also available to ease calculations. Description Name Value From Power Supply Specification: Minimum AC RMS Input (Turn-On) VLINE.ON Minimum AC RMS Input (Turn-Off) VLINE.OFF Minimum Line Frequency fLINE,MIN Nominal DC Output VOUT Output Voltage Ripple (2 · fLINE) VOUT,RIPPLE Latching Output OVP VOUT,LATCH Nominal Output Power (to Load) POUT Desired Hold-Up Time tHOLD Minimum DC Output (End of tHOLD) VOUT,MIN Minimum Switching Frequency fSW,MIN Maximum DC Bias (for FAN9611/12) VDDMAX Pre-Calculated Power Stage Parameters: Estimated Conversion Efficiency η 0.95 Maximum Output Power per Channel PMAX,CH Output Capacitance COUT Boost Inductance per Channel L Maximum On-Time per Channel tON,MAX Turns Ratio (NBOOST / NAUX) N 10 Other Variables Used During the Calculations: Peak Inductor Current IL,PK Maximum DC Output Current (to Load) IO,MAX Calculated Component Values: Zero Current Detect Resistor RZCD1, RZCD2 Bypass Capacitor for 5V Bias C5VB 0.15μ Maximum On-Time Set RMOT Soft-Start Capacitor CSS Compensation Capacitor CCOMP,LF Compensation Resistor RCOMP Compensation Capacitor CCOMP,HF Feedback Divider RFB1 Feedback Divider RFB2 Over Voltage Sense Divider ROV1 Over Voltage Sense Divider ROV2 Input Voltage Sense Divider RIN1 Input Voltage Sense Divider RIN2 Brownout Hysteresis Set RINHYST Gate Drive Resistor RG1, RG2 Gate Drive Speed-Up Diode DG1, DG2 Bypass Capacitor for VDD_HF CVDD1 2.2μ Startup Energy Storage for VDD CVDD2 47μ Current Sense Resistor RCS1, RCS2 Step 1: Input Voltage Range FAN9611/12 utilizes a single pin (VIN) for input voltage sensing. The VIN pin must be above 0.925V (VIN_BO) to enable operation. The converter turns on at a higher VIN voltage (VIN_ON) set independently by the designer. The input voltage information is used for feedforward in the control algorithm as well. The input-voltage feedforward operates over a four-to-one range from 0.925V (VIN_BO) to 3.7V (VFF_UL), as measured at the VIN pin. Figure 31. VIN Turn-on and Turn-off Thresholds At VIN voltages above the 3.7V upper limit (VFF_UL), input voltage feedforward is not possible. The input voltage- sense circuitry saturates at this point and the PWM ramp is modulated any longer. Above VFF_UL, the converter’s output power becomes a function of the input voltage as shown in Figure 32. It can also be expressed analytically as: 2 MAX OUT_NO_FF 3.7 VIN P P (5) where VIN is the voltage at the VIN pin and PMAX is the desired maximum output power of the converter which will be maintained constant while the input voltage feedforward circuit is operational. Figure 32. VIN Feedforward Range As can be seen, the converter’s output power capability will follow a square function above VFF_UL. |
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