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MIC5249-2.85YMM Datasheet(PDF) 6 Page - Micrel Semiconductor |
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MIC5249-2.85YMM Datasheet(HTML) 6 Page - Micrel Semiconductor |
6 / 7 page Micrel, Inc. MIC5249 March 2012 6 M9999-030812 Substituting PD(max) for PD and solving for the operating conditions that are critical to the application will give the maximum operating conditions for the regulator circuit. For example, when operating the MIC5249-3.0YMM at 50°C with a minimum footprint layout, the maximum input voltage for a set output current can be determined as follows: Thermal Considerations The MIC5249 is designed to provide 300mA of continuous current in a very small package. Maximum power dissipation can be calculated based on the output current and the voltage drop across the device. To determine the maximum power dissipation of the package, use the junction-to-ambient thermal resistance of the device and the following basic equation: ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ° ° − ° = C/W 160 C 50 C 125 P D(max) ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − = JA A J(max) D(max) θ T T P The junction-to-ambient thermal resistance for the minimum footprint is 160°C/W, from Table 1. The maximum power dissipation must not be exceeded for proper operation. Using the output voltage of 3.0V, and an output current of 300mA, the maximum input voltage can be determined. Because this device is CMOS and the ground current is typically 90µA over the load range, the power dissipation contributed by the ground current is < 1.0% and can be ignored for this calculation: TJ(max) is the maximum junction temperature of the die, 125°C and TA is the ambient operating temperature. θJA is layout dependent; Table 1 shows examples of the junction-to-ambient thermal resistance for the MIC5249. Package θ JA Recommended Minimum Footprint MSOP-8 160°C/W 468mW = (VIN – 3.0V) 300mA Table 1. MSOP-8 Thermal Resistance 468mW = VIN × 300mA – 900mW 1368mW = VIN × 300mA VIN(max) = 4.56V The actual power dissipation of the regulator circuit can be determined using the equation: Therefore, a 3.0V application at 300mA of output current can accept a maximum input voltage of 4.56V in the MSOP-8 package. For a full discussion of heat sinking and thermal effects on the voltage regulators, refer to the “Regulator Thermals” section of Micrel’s Designing with Low-Dropout Voltage Regulators Handbook . PD = (VIN – VOUT ) IOUT + VIN IGND |
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