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Zakładka z wyszukiwarką danych komponentów |
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Zakładka z wyszukiwarką danych komponentów |
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SPX2940 Arkusz danych(PDF) 7 Page - Exar Corporation |
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SPX2940 Arkusz danych(HTML) 7 Page - Exar Corporation |
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7 / 10 page  S SP PX X2 29 94 40 0 1 1A A L Lo ow w D Drro op po ou utt V Vo olltta ag ge e R Re eg gu ulla atto orr © 2009 Exar Corporation 7/10 Rev. 2.0.0 THEORY OF OPERATION The SPX2940 incorporates protection against over-current faults, reversed load insertion, over temperature operation, and positive and negative transient voltage. THERMAL CONSIDERATIONS Although the SPX2940 offers limiting circuitry for overload conditions, it is still necessary to insure that the maximum junction temperature is not exceeded in the application. Heat will flow through the lowest resistance path, the junction-to-case path. In order to insure the best thermal flow of the component, proper mounting is required. Since the case of the device is electrically connected to the output, the case must be electrically isolated using a thermally conductive spacer, which itself contributes some small additional thermal resistance. Consult heatsink manufacturer for thermal resistance and design of heatsink. TO-220 Design Example: Assume that VIN = 10V, VOUT = 5V, IOUT = 1.5A, TA = 50°C/W, θHA= 1°C/W, θCH = 2°C/W, and θJC = 3°C/W. Where TA = ambient temperature θHA = heatsink to ambient thermal resistance θCH = case to heatsink thermal resistance θJC = junction to case thermal resistance The power calculated under these conditions is: PD = (VIN – VOUT) * IOUT = 7.5W. And the junction temperature is calculated as TJ = TA + PD * (θHA + θCH + θJC) or TJ = 50 + 7.5 * (1 + 2 + 3) = 95°C Reliable operation is insured. CAPACITOR REQUIREMENTS The output capacitor is needed to insure stability and minimize the output noise. The value of the capacitor varies with the load. However, a minimum value of 10µF aluminum capacitor will guarantee stability over all load conditions. A tantalum capacitor is recommended if a faster load transient response is needed. If the power source has a high AC impedance, a 0.1µF ceramic capacitor between input & ground is recommended. MINIMUM LOAD CURRENT To ensure a proper behavior of the regulator under light load, a minimum load of 5mA for SPX2940 is required. consequat eu, consequat eu, ullamcorper pretium, magna. Aenean varius turpis sed metus. Donec erat. Nunc urna pede, accumsan sed, tristique non, lobortis sit amet, pede. Fig. 20: Fixed Output Linear Regulator Fig. 21: Ouput Cap ESR vs IOUT Fig. 22: 5.0VOUT PSSR VIN=10V, VOUT=5V COUT=22F, IOUT=10mA |
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