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MIC5225-2.5YM5 Datasheet(PDF) 7 Page - Micrel Semiconductor |
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MIC5225-2.5YM5 Datasheet(HTML) 7 Page - Micrel Semiconductor |
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7 / 9 page  Micrel, Inc. MIC5225 July 2008 7 M9999-072908-A Application Information Enable/Shutdown The MIC5225 comes with an active-high enable pin that allows the regulator to be disabled. Forcing the enable pin lows disables the regulator and sends it into a “zero” off-mode current state. In this state, current consumed by the regulator goes nearly to zero. Forcing the enable pin high enables the output voltage. Input Capacitor The MIC5225 has a wide input voltage capability up to 16V. The input capacitor must be rated to sustain voltages that may be used on the input. An input capacitor may be required when the device is not near the source power supply or when supplied by a battery. Small, surface mount, ceramic capacitors can be used for bypassing. Larger value may be required if the source supply has high ripple. Output Capacitor The MIC5225 requires an output capacitor for stability. The design requires 1.0µF or greater on the output to maintain stability. The design is optimized for use with low-ESR ceramic chip capacitors. High ESR capacitors may cause high frequency oscillation. The maximum recommended ESR is 300mΩ. The output capacitor can be increased, but performance has been optimized for a 1.0µF ceramic output capacitor and does not improve significantly with the use of a larger capacitor. X7R/X5R dielectric-type ceramic capacitors are recommended because of their temperature performance. X7R-type capacitors change capacitance by 15% over their operating temperature range and are the most stable type of ceramic capacitors. Z5U and Y5V dielectric capacitors change value by as much as 50% and 60% respectively over their operating temperature ranges. To use a ceramic chip capacitor with Y5V dielectric, the value must be much higher than an X7R ceramic capacitor to ensure the same minimum capacitance over the equivalent operating temperature range. No-Load Stability The MIC5225 will remain stable and in regulation with no load unlike many other voltage regulators. This is especially important in CMOS RAM keep-alive applications. Thermal Consideration The MIC5225 is designed to provide 150mA 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 part. To determine the maximum power dissipation of the package, use the junction-to-ambient thermal resistance of the device and the following basic equation: PD(MAX) = (TJ(MAX) – TA)/θJA TJ(MAX) is the maximum junction temperature of the die, 125 °C, and T A is the ambient operating temperature. θJA is layout dependent; Table 1 shows examples of the junction-to-ambient thermal resistance for the MIC5225. Package θJA Recommended Minimum Footprint SOT-23-5 235 oC/W Table 1. SOT-23-5 Thermal Resistance The actual power dissipation of the regulator circuit can be determined using the equation: PD = (VIN – VOUT)IOUT + VINIGND 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 MIC5225-3.0BMM at 50 °C with a minimum footprint layout, the maximum input voltage for a set output current can be determined as follows: PD(MAX) = (125 oC – 50oC)/ 235oC/W PD(MAX) = 319mW The junction-to-ambient thermal resistance for the minimum footprint is 235 °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 150mA, the maximum input voltage can be determined. 319mW = (VIN – 3.0V)150mA + VIN × 3.0mA 319mW = VIN × 153mA – 450mW 769mW = VIN × 153mA VIN(MAX) = 5.02V Therefore, a 3.0V application at 150mA of output current can accept a maximum input voltage of 5.02V in the SOT-23-5 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: http://www.onfulfillment.com/estore/pdf_download.asp? s=2243381&p=18&pdf=842935-iecjdf-bicadii |
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