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MIC5205-3.6YM5 Datasheet(PDF) 8 Page - Micrel Semiconductor |
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MIC5205-3.6YM5 Datasheet(HTML) 8 Page - Micrel Semiconductor |
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8 / 10 page  Micrel MIC5205 February 2006 8 M9999-020806 (408) 955-1690 Application Information Enable/Shutdown Forcing EN (enable/shutdown) high (> 2V) enables the regulator. EN is compatible with CMOS logic gates. If the enable/shutdown feature is not required, connect EN (pin 3) to IN (supply input, pin 1). See Figure 1. Input Capacitor A 1µF capacitor should be placed from IN to GND if there is more than 10 inches of wire between the input and the ac filter capacitor or if a battery is used as the input. Reference Bypass Capacitor BYP (reference bypass) is connected to the internal voltage reference. A 470pF capacitor (CBYP) connected from BYP to GND quiets this reference, providing a significant reduction in output noise. CBYP reduces the regulator phase margin; when using CBYP, output capacitors of 2.2µF or greater are generally required to maintain stability. The start-up speed of the MIC5205 is inversely proportional to the size of the reference bypass capacitor. Applications requiring a slow ramp-up of output voltage should consider larger values of CBYP. Likewise, if rapid turn-on is necessary, consider omitting CBYP. If output noise is not a major concern, omit CBYP and leave BYP open. Output Capacitor An output capacitor is required between OUT and GND to prevent oscillation. The minimum size of the output capacitor is dependent upon whether a reference bypass capacitor is used. 1.0µF minimum is recommended when CBYP is not used (see Figure 2). 2.2µF minimum is recommended when CBYP is 470pF (see Figure 1). Larger values improve the regulator’s transient response. The output capacitor value may be increased without limit. The output capacitor should have an ESR (effective series resistance) of about 5Ω or less and a resonant frequency above 1MHz. Ultra-low-ESR capacitors can cause a low amplitude oscillation on the output and/or underdamped transient response. Most tantalum or aluminum electrolytic capacitors are adequate; film types will work, but are more expensive. Since many aluminum electrolytics have electrolytes that freeze at about – 30 °C, solid tantalums are recommended for operation below –25 °C. At lower values of output current, less output capacitance is required for output stability. The capacitor can be reduced to 0.47 ⎧F for current below 10mA or 0.33µF for currents below 1mA. No-Load Stability The MIC5205 will remain stable and in regulation with no load (other than the internal voltage divider) unlike many other voltage regulators. This is especially important in CMOS RAM keep-alive applications. Thermal Considerations The MIC5205 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: ( ) JA A J(max) D(max) θ T T P − = 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 junction-toambient thermal resistance for the MIC5205. Package θJA Recommended Minimum Footprint θJA Square Copper Clad θJC SOT-23-5(M5) 220°C/W 170°C/W 130°C/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 + VIN IGND 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 MIC5205-3.3BM5 at room temperature with a minimum footprint layout, the maximum input voltage for a set output current can be determined as follows: ( ) 455mW P C/W 220 C 25 C 125 P D(max) D(max) = ° ° − ° = The junction-to-ambient thermal resistance for the minimum footprint is 220 °C/W, from Table 1. The maximum power dissipation must not be exceeded for proper operation. Using the output voltage of 3.3V and an output current of 150mA, the maximum input voltage can be determined. From the Electrical Characteristics table, the maximum ground current for 150mA output current is 2500µA or 2.5mA. 455mW = (VIN – 3.3V) 150mA + VIN·2.5mA 455mW = VIN×150mA – 495mW + VIN·2.5mA 950mW = VIN×152.5mA |
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