поискавой системы для электроныых деталей |
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CS8121 датащи(PDF) 7 Page - Cherry Semiconductor Corporation |
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CS8121 датащи(HTML) 7 Page - Cherry Semiconductor Corporation |
7 / 8 page Step 6: Test the load transient response by switching in various loads at several frequencies to simulate its real working environment. Vary the ESR to reduce ringing. Step 7: Remove the unit from the environmental chamber and heat the IC with a heat gun. Vary the load current as instructed in step 5 to test for any oscillations. 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 regula- tor 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. The maximum power dissipation for a single output regu- lator (Figure 7) 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 applica- tion, and IQ is the quiescent current the regulator consumes at IOUT(max). Once the value of PD(max) is known, the maximum permis- sible value of RQJA can be calculated: RQJA = (2) The value of RQJA can then be compared with those in the package section of the data sheet. Those packages with RQJA'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. 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 RQJA: RQJA = RQJC + RQCS + RQSA (3) where: RQJC = the junctionÐtoÐcase thermal resistance, RQCS = the caseÐtoÐheatsink thermal resistance, and RQSA = the heatsinkÐtoÐambient thermal resistance. RQJC appears in the package section of the data sheet. Like RQJA, it too is a function of package type. RQCS and RQSA are functions of the package type, heatsink and the inter- face between them. These values appear in heat sink data sheets of heat sink manufacturers. 150¡C - T A PD 7 Application Notes: continued Calculating Power Dissipation in a Single Output Linear Regulator VIN Smart Regulator VOUT IOUT IIN IQ Control Features } Figure 7: Single output regulator with key performance parameters labeled. RESET VOUT RRST C2** 10 mF CRST ENABLE VIN C1* 0.1 mF to mP RESET Port 5V to mP and System Power CS-8121 C1*required if regulator is located far from the power supply filter. C2** required for stability. Heat Sinks Figure 6: Test and application circuit showing output compensation. |
Аналогичный номер детали - CS8121 |
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Аналогичное описание - CS8121 |
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