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CS8221YDFR8 Fiches technique(PDF) 5 Page - ON Semiconductor |
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CS8221YDFR8 Fiches technique(HTML) 5 Page - ON Semiconductor |
5 / 7 page CS8221 http://onsemi.com 5 Once the minimum capacitor value with the maximum ESR is found, a safety factor should be added to allow for the tolerance of the capacitor and any variations in regulator performance. Most good quality aluminum electrolytic capacitors have a tolerance of ± 20% so the minimum value found should be increased by at least 50% to allow for this tolerance plus the variation which will occur at low temperatures. The ESR of the capacitor should be less than 50% of the maximum allowable ESR found in step 3 above. CALCULATING POWER DISSIPATION IN A SINGLE OUTPUT LINEAR REGULATOR The maximum power dissipation for a single output regulator (Figure 5) is: PD(max) + VIN(max) * VOUT(min) IOUT(max) ) VIN(max)IQ (1) where: VIN(max) is the maximum input voltage, VOUT(min) is the minimum output voltage, IOUT(max) is the maximum output current for the application, and IQ is the quiescent current the regulator consumes at IOUT(max). Once the value of PD(max) is known, the maximum permissible value of RΘJA can be calculated: R QJA + 150 °C * TA PD (2) The value of RΘJA can then be compared with those in the package section of the data sheet. Those packages with RΘJA’s less than the calculated value in equation 2 will keep the die temperature below 150 °C. In some cases, none of the packages will be sufficient to dissipate the heat generated by the IC, and an external heatsink will be required. Figure 5. Single Output Regulator With Key Performance Parameters Labeled CS8221 IOUT IIN IQ VIN VOUT HEAT SINKS A heat sink effectively increases the surface area of the package to improve the flow of heat away from the IC and into the surrounding air. Each material in the heat flow path between the IC and the outside environment will have a thermal resistance. Like series electrical resistances, these resistances are summed to determine the value of RΘJA. R QJA + RQJC ) RQCS ) RQSA (3) where: RΘJC = the junction−to−case thermal resistance, RΘCS = the case−to−heatsink thermal resistance, and RΘSA = the heatsink−to−ambient thermal resistance. RΘJC appears in the package section of the data sheet. Like RΘJA, it too is a function of package type. RΘCS and RΘSA are functions of the package type, heatsink and the interface between them. These values appear in heat sink data sheets of heat sink manufacturers. |
Numéro de pièce similaire - CS8221YDFR8 |
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Description similaire - CS8221YDFR8 |
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