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MIC5239-2.5BMM Datasheet(PDF) 11 Page - Micrel Semiconductor |
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MIC5239-2.5BMM Datasheet(HTML) 11 Page - Micrel Semiconductor |
11 / 14 page Micrel MIC5239 December 2007 11 M9999-121007 ∆T = TJ(max) – TA(max) TJ(max) = 125°C TA(max) = maximum ambient operating temperature For example, the maximum ambient temperature is 50°C, the ∆T is determined as follows: ∆T = 125°C – 50°C ∆T = 75°C Using Figure 6, the minimum amount of required copper can be determined based on the required power dissipation. Power dissipation in a linear regulator is calculated as follows: PD = (VIN – VOUT) IOUT + VIN × IGND If we use a 3V output device and a 28V input at moderate output current of 25mA, then our power dissipation is as follows: PD = (28V – 3V) × 25mA + 28V 250µA PD = 625mW + 7mW PD = 632mW From Figure 6, the minimum amount of copper required to operate this application at a ∆T of 75°C is 110mm 2. Quick Method Determine the power dissipation requirements for the design along with the maximum ambient temperature at which the device will be operated. Refer to Figure 7, which shows safe operating curves for three different ambient temperatures: 25°C, 50°C and 85°C. From these curves, the minimum amount of copper can be determined by knowing the maximum power dissipation required. If the maximum ambient temperature is 50°C and the power dissipation is as above, 639mW, the curve in Figure 7 shows that the required area of copper is 110mm 2. The θJA of this package is ideally 80°C/W, but it will vary depending upon the availability of copper ground plane to which it is attached. Figure 7. Copper Area vs. Power-MSOP Power Dissipation (T A) Figure 8. Copper Area vs. Power-SOIC Power Dissipation (∆T JA) Figure 9. Copper Area vs. Power-SOIC Power Dissipation (T A) The same method of determining the heatsink area used for the power MSOP-8 can be applied directly to the power SOIC-8. The same two curves showing power dissipation versus copper area are reproduced for the power SOIC-8 and they can be applied identically. Power SOIC-8 Thermal Characteristics The power SOIC-8 package follows the same idea as the power MSOP-8 package, using four ground leads with the die attach paddle to create a single-piece electrical and thermal conductor, reducing thermal resistance and increasing power dissipation capability. Quick Method Determine the power dissipation requirements for the design along with the maximum ambient temperature at which the device will be operated. Refer to Figure 9, which shows safe operating curves for three different ambient temperatures, 25°C, 50°C, and 85°C. From these curves, the minimum amount of copper can be determined by knowing the maximum power dissipation required. If the maximum ambient temperature is 50°C, and the power dissipation is 632mW, the curve in Figure 9 shows that the required area of copper is less than 100mm2, when using the power SOIC-8. |
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