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NCP1654BD133R2G Datasheet(PDF) 15 Page  ON Semiconductor 

NCP1654BD133R2G Datasheet(HTML) 15 Page  ON Semiconductor 
15 / 23 page NCP1654 http://onsemi.com 15 RboL is low side resistor of the dividing resistors between Vin and BO pin. RboU is upper side resistor of the dividing resistors between Vin and BO pin. Figure 37. Current Sensing Gnd + RSENSE IL RCS ICS CS VCS NCP1654 + − IL Refer to Figure 37, sense current Ics is proportional to the inductor current IL as described in (Equation 11). IL consists of the high−frequency component (that depends on di/dt or inductor L) and low−frequency component (that is IL−50). (eq. 11) Ics + RSENSE RCS IL where RSENSE is the sense resistor to sense IL. RCS is the offset resistor between CS pin and RSENSE. Figure 38. Vcontrol Low−Pass Filtering +  VREF OTA 6 5 Vcontrol ±20 mA Vout + + VCONTROL(min) To Vm Pin Vfb RZ CZ CP RfbL RfbU Vin Refer to Figure 38, the Operational Trans−conductance Amplifier (OTA) senses Vout via the feedback resistor dividers, RfbU and RfbL. The OTA constructs a control voltage, Vcontrol, depending on the output power and hence Vout. The operating range of Vcontrol is from VCONTROL(min) to VCONTROL(max). The signal used for PFC duty modulation is after decreasing a offset voltage, VCONTROL(min), i.e. Vcontrol−VCONTROL(min). This control current Icontrol is a roughly constant current that comes from the PFC output voltage Vout that is a slowly varying signal. The bandwidth of Icontrol can be additionally limited by inserting the external type−2 compensation components (that are RZ, CZ, and CP as shown in Figure 38). It is recommended to limit fcontrol, that is the bandwidth of Vcontrol (or Icontrol), below 20 Hz typically to achieve power factor correction purpose. The transformer of Vout to Vcontrol is as described in (Equation 12) if CZ is >> CP. GEA is the error amplifier gain. Vcontrol Vout + RfbL @ GEARZ RfbL ) RfbU @ 1 ) sRZCZ sRZCZ(1 ) sRZCP) (eq. 12) From (Equation 7) − (Equation 11), the input impedance Zin is re−formulated in (Equation 13). Zin + 2 RMRSENSEVoutVacKBOIL 2pRCS @ (Vcontrol * VCONTROL(min)) @ VREFIL*50 (eq. 13) When IL is equal to IL−50, (Equation 13) is re−formulated in (Equation 14) Zin + 2 RMRSENSEVoutVacKBO 2pRCS @ (Vcontrol * VCONTROL(min)) @ VREF (eq. 14) The multiplier capacitor CM is the one to filter the high−frequency component of the multiplier voltage Vm. The high−frequency component is basically coming from the inductor current IL. On the other hand, the filter capacitor Cfilter similarly removes the high−frequency component of inductor current IL. If the capacitors CM and Cfiltermatch with each other in terms of filtering capability, IL becomes IL−50. Input impedance Zin is roughly constant over the bandwidth of 50 or 60 Hz and power factor is corrected. 
