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MIC5216-3.6BMM Datasheet(PDF) 6 Page - Micrel Semiconductor |
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MIC5216-3.6BMM Datasheet(HTML) 6 Page - Micrel Semiconductor |
6 / 12 page MIC5216 Micrel MIC5216 6 January 2000 Applications Information The MIC5216 is designed for 150mA to 200mA output current applications where a high current spike (500mA) is needed for short, startup conditions. Basic application of the device will be discussed initially followed by a more detailed discus- sion of higher current applications. Enable/Shutdown Forcing EN (enable/shutdown) high (> 2V) enables the regu- lator. EN is compatible with CMOS logic. If the enable/ shutdown feature is not required, connect EN to IN (supply input). See Figure 5. Input Capacitor A 1 µF 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. Output Capacitor An output capacitor is required between OUT and GND to prevent oscillation. 1 µF minimum is recommended. Larger values improve the regulator’s transient response. The out- put capacitor value may be increased without limit. The output capacitor should have an ESR (equivalent series resistance) of about 5 Ω or less and a resonant frequency above 1MHz. Ultralow-ESR capacitors could cause oscilla- tion and/or underdamped transient response. Most tantalum or aluminum electrolytic capacitors are adequate; film types will work, but more expensive. Many aluminum electrolytics have electrolytes that freeze at about –30 °C, so solid tanta- lums are recommended for operation below –25 °C. At lower values of output current, less output capacitance is needed for stability. The capacitor can be reduced to 0.47 µF for current below 10mA or 0.33 µF for currents below 1mA. No-Load Stability The MIC5216 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. Error Flag Ouput The error flag is an open-collector output and is active (low) when an undervoltage of approximately 5% below the nomi- nal output voltage is detected. A pullup resistor from IN to FLAG is shown in all schematics. If an error indication is not required, FLAG may be left open and the pullup resistor may be omitted. Thermal Considerations The MIC5216 is designed to provide 200mA of continuous current in two very small profile packages. 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 thermal resistance, junction-to-ambient, of the device and the following basic equation. P = T – T D(MAX) J(MAX) A JA () θ T J(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 thermal resis- tance, junction-to-ambient, for the MIC5216. Package θθθθθ JA Recommended θθθθθ JA 1" Square θθθθθ JC Minimum Footprint Copper Clad MM8™ (MM) 160 °C/W 70 °C/W 30 °C/W SOT-23-5 (M5) 220 °C/W 170 °C/W 130 °C/W Table 1. MIC5216 Thermal Resistance The actual power dissipation of the regulator circuit can be determined using one simple equation. P D = (VIN – VOUT) IOUT + VIN IGND Substituting P D(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, if we are operating the MIC5216-3.3BM5 at room temperature, with a minimum footprint layout, we can deter- mine the maximum input voltage for a set output current. P = 125 C – 25 C C/W D(MAX) °° () ° 220 P 455mW D(MAX) = The thermal resistance, junction-to-ambient, for the mini- mum footprint is 220 °C/W, taken from table 1. The maximum power dissipation number cannot be exceeded for proper operation of the device. Using the output voltage of 3.3V, and an output current of 150mA, we can determine the maximum input voltage. Ground current, maximum of 3mA for 150mA of output current, can be taken from the Electrical Character- istics section of the data sheet. 455mW = (V IN – 3.3V) 150mA + VIN × 3mA V 455mW + 3.3V 150mA mA + 3mA IN () 150 V 6.2V IN MAX = Therefore, a 3.3V application at 150mA of output current can accept a maximum input voltage of 6.2V in a SOT-23-5 package. For a full discussion of heat sinking and thermal effects on voltage regulators, refer to the Regulator Thermals section of Micrel’s Designing with Low-Dropout Voltage Regu- lators handbook. Peak Current Applications The MIC5216 is designed for applications where high start- up currents are demanded from space constrained regula- tors. This device will deliver 500mA start-up current from a SOT-23-5 or MM8 package, allowing high power from a very low profile device. The MIC5216 can subsequently provide output current that is only limited by the thermal characteris- tics of the device. You can obtain higher continuous currents from the device with the proper design. This is easily proved with some thermal calculations. If we look at a specific example, it may be easier to follow. The MIC5216 can be used to provide up to 500mA continuous |
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