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CS8156 Fiches technique(PDF) 8 Page - ON Semiconductor |
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CS8156 Fiches technique(HTML) 8 Page - ON Semiconductor |
8 / 11 page CS8156 http://onsemi.com 8 appear. Record the values of load current and ESR that cause the greatest oscillation. This represents the worst case load conditions for the regulator at low temperature. Step 4: Maintain the worst case load conditions set in step 3 and vary the input voltage until the oscillations increase. This point represents the worst case input voltage conditions. Step 5: If the capacitor is adequate, repeat steps 3 and 4 with the next smaller valued capacitor. A smaller capacitor will usually cost less and occupy less board space. If the output oscillates within the range of expected operating conditions, repeat steps 3 and 4 with the next larger standard capacitor value. 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: Raise the temperature to the highest specified operating temperature. 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 for each output, 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 capacitors should be less than 50% of the maximum allowable ESR found in step 3 above. Repeat steps 1 through 7 with C3, the capacitor on the other output. Calculating Power Dissipation in a Dual Output Linear Regulator The maximum power dissipation for a dual output regulator (Figure 20) is PD(max) + VIN(max) * VOUT1(min) IOUT1(max) ) VIN(max) * VOUT2(min) IOUT2(max) ) VIN(max)IQ (1) where: VIN(max) is the maximum input voltage, VOUT1(min) is the minimum output voltage from VOUT1, VOUT2(min) is the minimum output voltage from VOUT2, IOUT1(max) is the maximum output current, for the application, IOUT2(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 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 20. Dual Output Regulator With Key Performance Parameters Labeled. Smart Regulator Control Features VOUT1 IOUT1 VOUT2 IOUT2 VIN IIN IQ 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. Figure 21. Test & Application Circuit CS8156 VOUT1 VOUT2 ENABLE GND VIN + + * C1 is required if the regulator is far from power supply filter. ** C2, C3 required for stability. C1* 0.1 μF C2** 22 μF C3** 22 μF |
Numéro de pièce similaire - CS8156 |
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Description similaire - CS8156 |
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