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CS8161YT5G 数据表(PDF) 8 Page - ON Semiconductor |
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CS8161YT5G 数据表(HTML) 8 Page - ON Semiconductor |
8 / 11 page CS8161 http://onsemi.com 8 The values for the output capacitors C2 and C3 shown in the test and applications circuit should work for most applications, however it is not necessarily the best solution. To determine acceptable values for C2 and C3 for a particular application, start with tantalum capacitors of the recommended value on each output and work towards less expensive alternative parts for each output in turn. Step 1: Place the completed circuit with a tantalum capacitor of the recommended value in an environmental chamber at the lowest specified operating temperature and monitor the outputs on the oscilloscope. A decade box connected in series with the capacitor C2 will simulate the higher ESR of an aluminum capacitor.(Leave the decade box outside the chamber, the small resistance added by the longer leads is negligible) Step 2: With the input voltage at its maximum value, increase the load current slowly from zero to full load while observing the output for any oscillations. If no oscillations are observed, the capacitor is large enough to ensure a stable design under steady state conditions. Step 3: Increase the ESR of the capacitor from zero using the decade box and vary the load current until oscillations 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 C2 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 capacitor 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 work 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, 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. Once the value for C2 is determined, repeat the steps to determine the appropriate value for C3. Calculating Power Dissipation in a Dual Output Linear Regulator The maximum power dissipation for a dual output regulator (Figure 19) 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 RqJA can be calculated: R qJA + 150 °C * TA PD (2) The value of RqJA can 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. Figure 19. Dual Output Regulator With Key Performance Parameters Labeled. Smart Regulator Control Features VOUT1 IOUT1 VOUT2 IOUT2 VIN IIN IQ |
类似零件编号 - CS8161YT5G |
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类似说明 - CS8161YT5G |
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