Datenblatt-Suchmaschine für elektronische Bauteile |
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SD46520 Datenblatt(PDF) 6 Page - Silan Microelectronics Joint-stock |
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SD46520 Datenblatt(HTML) 6 Page - Silan Microelectronics Joint-stock |
6 / 8 page SD46520 Where, is output voltage ripple, is inductor current ripple, ESR is the equivalent serial resistor of output capacitor. O ΔV L ΔI The freewheeling diode selection Select the schottky diode as freewheeling diode to reduce the loss caused by forward voltage drop of the diode. At the same time, the maximum current of schottky should be higher than 2.4A. Compensation network The resistor-capacitor compensation network connected to COMP pin make sure the stability of the control loop circuit. As the right figure: The DC gain of the control loop is: L CS VEA O FB VDC R G A V V A ⋅ ⋅ ⋅ = Where, VFB is feedback voltage, 1.22V; VO is setting output voltage; AVEA is the voltage gain of error amplifier, 400V/V; GCS is the trans-conductance of current sense(about the value of the output current divided by COMP pin voltage), 1.95A/V; RL is load resistor. The control loop has two poles of inportance. HANGZHOU SILAN MICROELECTRONICS CO.,LTD REV:1.0 2009.04.07 Http://www.silan.com.cn Page 6 of 8 The first pole P1 is decided by the following formula: C1 OEA P1 C R 2π 1 ⋅ ⋅ = f , where, EA VEA OEA G A = R , GEA is the trans-conductance of error amplifier, 770uA/V. The second pole P2 is decided by: O L P2 C R 2 1 ⋅ ⋅ = π f 。 The control loop has a main zero Z1, which is decided by: C1 C Z1 C R 2 1 f ⋅ ⋅ = π 。 When the output capacitor ESR is large, another zero Z2 is introduced which is decided by: O Z2 C ESR 2 1 f ⋅ ⋅ = π . At this time, it needs to add another compensation capacitor Cc2 to introduce an additional pole P3 compensate this zero , and this pole is decided by: C2 C P3 C R 2 1 f ⋅ ⋅ = π The system crossover frequency fC is very important. If it’s too high , it will cause the system unstable. If it’s too low, it will slower the system transient response. In general, fC is about 1/8~1/10 of the switch frequency. Use the following procedure to choose the value of the compensation components. First, according to the selected crossover crossover fC, choose the value of compensation resistor Rc: |
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