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CS51413GD8 Fiches technique(PDF) 8 Page - ON Semiconductor |
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CS51413GD8 Fiches technique(HTML) 8 Page - ON Semiconductor |
8 / 20 page CS51411, CS51412, CS51413, CS51414 http://onsemi.com 8 Control Ramp Generation In original V2 designs, the control ramp VCR was generated from the converter’s output ripple. Using a current derived ramp provides the same benefits as current mode, namely input feed forward, single pole output filter compensation and fast feedback following output load transients. Typically a tantalum or organic polymer capacitor is selected having a sufficiently large ESR component, relative to its capacitive and ESL ripple contributions, to ensure the control ramp was sensing inductor current and its amplitude was sufficient to maintain loop stability. This technique is illustrated in Figure 6. Figure 6. Control Ramp Generated from Output VIN VOUT L Cesr C VFB Advances in multilayer ceramic capacitor technology are such that MLCC’s can provide a cost effective filter solution for low voltage (< 12 V), high frequency converters (>200 kHz). For example, a 10 mF MLCC 16 V in a 805 SMT package has an ESR of 2 m W and an ESL of 100 nH. Using several MLCC’s in parallel, connected to power and ground planes on a PCB with multiple vias, can provide a “near perfect” capacitor. Using this technique, output switching ripple below 10 mV can be readily obtained since parasitic ESR and ESL ripple contributions are nil. In this case, the control ramp is generated elsewhere in the circuit. Ramp generation using dcr inductor current sensing, where the L/DCR time constant of the output inductor is matched with the CR time constant of the integrating network, is shown in Figure 7. The converter’s transient response following a 1 A step load is shown in Figure 8. This transient response is indicative of a closed loop in excess of 10 kHz having good gain and phase margin in the frequency domain. Also note the amplitude of output switching ripple provided by just two 10 mF MLCC’s. Figure 7. Control Ramp Generated from DCR Inductor Sensing VIN VOUT C R VFB Figure 8. Ramp generation using a voltage feed forward technique is illustrated in Figure 9. Figure 9. Control Ramp from Voltage Feed Forward VIN VOUT Rf Cf CZ VFB |
Numéro de pièce similaire - CS51413GD8 |
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Description similaire - CS51413GD8 |
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