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NCP1402 Fiches technique(PDF) 15 Page - ON Semiconductor |
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NCP1402 Fiches technique(HTML) 15 Page - ON Semiconductor |
15 / 18 page NCP1402 http://onsemi.com 15 APPLICATIONS CIRCUIT INFORMATION 1 3 GND CE 2 OUT NC 4 LX 5 NCP1402 Figure 59. Typical Application Circuit VOUT C2 68 mF D1 L1 47 mH C1 10 mF Vin Step−up Converter Design Equations NCP1402 step−up DC−DC converter designed to operate in continuous conduction mode can be defined by: Calculation Equation L v M Vin2 VOUT IOmax IPK (Vin * Vs)ton L ) I min Imin (ton ) toff)IO toff * (Vin * VS)ton 2L toff (Vin * Vs)ton (VOUT ) VF * Vin) DQ (IL * IO)toff Vripple [ DQ COUT ) (IL * IO)ESR *NOTES: IPK − Peak inductor current Imin − Minimum inductor current IO − Desired dc output current IOmax − Desired maximum dc output current IL − Average inductor current Vin − Nominal operating dc input voltage VOUT − Desired dc output voltage VF − Diode forward voltage VS − Saturation voltage of the internal FET switch DQ − Charge stores in the COUT during charging up Vripple − Output ripple voltage ESR − Equivalent series resistance of the output capacitor M − An empirical factor, when VOUT ≥ 3.0 V, M = 8 x 10−6, otherwise M = 5.3 x 10−6. EXTERNAL COMPONENT SELECTION Inductor The NCP1402 is designed to work well with a 47 mH inductor in most applications. 47 mH is a sufficiently low value to allow the use of a small surface mount coil, but large enough to maintain low ripple. Low inductance values supply higher output current, but also increase the ripple and reduce efficiency. Note that values below 27 mH is not recommended due to NCP1402 switch limitations. Higher inductor values reduce ripple and improve efficiency, but also limit output current. The inductor should have small DCR, usually less than 1 W to minimize loss. It is necessary to choose an inductor with saturation current greater than the peak current which the inductor will encounter in the application. Diode The diode is the main source of loss in DC−DC converters. The most importance parameters which affect their efficiency are the forward voltage drop, VF, and the reverse recovery time, trr. The forward voltage drop creates a loss just by having a voltage across the device while a current flowing through it. The reverse recovery time generates a loss when the diode is reverse biased, and the current appears to actually flow backwards through the diode due to the minority carriers being swept from the P−N junction. A Schottky diode with the following characteristics is recommended: Small forward voltage, VF < 0.3 V Small reverse leakage current Fast reverse recovery time/ switching speed Rated current larger than peak inductor current, Irated > IPK Reverse voltage larger than output voltage, Vreverse > VOUT Input Capacitor The input capacitor can stabilize the input voltage and minimize peak current ripple from the source. The value of the capacitor depends on the impedance of the input source used. Small Equivalent Series Resistance (ESR) Tantalum or ceramic capacitor with value of 10 mF should be suitable. |
Numéro de pièce similaire - NCP1402_06 |
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Description similaire - NCP1402_06 |
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