Zakładka z wyszukiwarką danych komponentów |
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CS51221EDTB16G Arkusz danych(PDF) 11 Page - ON Semiconductor |
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CS51221EDTB16G Arkusz danych(HTML) 11 Page - ON Semiconductor |
11 / 14 page CS51221 http://onsemi.com 11 0.0001 0.001 0.01 CT (mF) 0 800 400 700 600 500 300 200 100 1000 10000 1000000 RT (W) 0.50 1.00 0.80 0.95 0.90 0.85 0.75 0.70 0.65 0.60 0.55 100000 Figure 10. Typical Performance Characteristics, Oscillator Frequency vs. CT Figure 11. Typical Performance Characteristics, Oscillator Duty Cycle vs. RT RT = 5.0 K RT = 10 K RT = 50 K that during steady state, VCOMP doesn’t change for input voltage variations. This intuitively explains why FF voltage mode control has superior line regulation and line transient response. Knowing the nominal value of VIN and TON, one can also select the value of RC to place VCOMP at the center of its dynamic range. Select Feedback Voltage Divider As shown in Figure 12, the voltage divider output feeds to the FB pin, which connects to the inverting input of the error amplifier. The non−inverting input of the error amplifier is connected to a 1.27 V (typ) reference voltage. The FB pin has an input current which has to be considered for accurate DC outputs. The following equation can be used to calculate the R1 and R2 value R2 R1 ) R2 VOUT + 1.27 * where ∇ is the correction factor due to the existence of the FB pin input current Ier. + (Ri ) R1 R2)Ier Ri = DC resistance between the FB pin and the voltage divider output. Ier = VFB input current, 1.3 mA typical. Design Voltage Dividers for OV and UV Detection In Figure 13, the voltage divider uses three resistors in series to set OV and UV threshold seen from the input voltage. The values of the resistors can be calculated from the following three equations, where the third equation is derived from OV hysteresis requirement. VIN(LOW) R2 ) R3 R2 ) R3 ) R1 + 1.0 V (A) VIN(HIGH) R3 R2 ) R3 ) R1 + 2.0 V (B) 12.5 mA (R1 ) R2) + VHYST (C) where: VIN(LOW), VIN(HIGH) = input voltage OV and UV threshold; VHYST = OV hysteresis seen at VIN It is self−evident from equation A and B that to use this design, VIN(HIGH) has to be two times greater than VIN(LOW). Otherwise, two voltage dividers have to be used to program OV and UV separately. Figure 12. The Design of Feedback Voltage Divider Has to Consider the Error Amplifier Input Current + − − + VOUT R1 COMP FB R2 Ri 1.27 Ier Figure 13. OV/UV Monitor Divider VIN R1 R2 R3 VUV VOV |
Podobny numer części - CS51221EDTB16G |
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Podobny opis - CS51221EDTB16G |
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