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MIC3775-3.0YMM Datasheet(PDF) 10 Page - Micrel Semiconductor |
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MIC3775-3.0YMM Datasheet(HTML) 10 Page - Micrel Semiconductor |
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10 / 13 page  Micrel, Inc. MIC3775 December 2006 10 M9999-121906 Application Information The MIC3775 is a high-performance low-dropout voltage regulator suitable for moderate to high-current voltage regulator applications. Its 500mV dropout voltage at full load and overtemperature makes it especially valuable in battery-powered systems and as high-efficiency noise filters in post-regulator applications. Unlike older NPN- pass transistor designs, where the minimum dropout voltage is limited by the base-to-emitter voltage drop and collector-to-emitter saturation voltage, dropout perform- ance of the PNP output of these devices is limited only by the low VCE saturation voltage. A trade-off for the low-dropout voltage is a varying base drive requirement. Micrel’s Superβeta PNP ® process reduces this drive requirement to only 2% of the load current. The MIC3775 regulator is fully protected from damage due to fault conditions. Linear current limiting is provided. Output current during overload conditions is constant. Thermal shutdown disables the device when the die temperature exceeds the maximum safe operating temperature. The output structure of these regulators allows voltages in excess of the desired output voltage to be applied without reverse current flow. Figure 1. Capacitor Requirements Output Capacitor The MIC3775 requires an output capacitor for stable operation. As a µCap LDO, the MIC3775 can operate with ceramic output capacitors as long as the amount of capacitance is 10µF or greater. For values of output capacitance lower than 10µF, the recommended ESR range is 200mΩ to 2Ω. The minimum value of output capacitance recommended for the MIC3775 is 4.7µF. For 10µF or greater the ESR range recommended is less than 1Ω. Ultra-low ESR ceramic capacitors are recommended for output capacitance of 10µF or greater to help improve transient response and noise reduction at high frequency. 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. Input Capacitor An input capacitor of 1µF or greater is recommended when the device is more than 4 inches away from the bulk AC supply capacitance or when the supply is a battery. Small, surface mount, ceramic chip capacitors can be used for bypassing. Larger values will help to improve ripple rejection by bypassing the input to the regulator, further improving the integrity of the output voltage. Error Flag The MIC3775 features an error flag (FLG), which monitors the output voltage and signals an error condition when this voltage drops 5% below its expected value. The error flag is an open-collector output that pulls low under fault conditions and may sink up to 10mA. Low output voltage signifies a number of possible problems, including an overcurrent fault (the device is in current limit) or low input voltage. The flag output is inoperative during overtemperature conditions. A pull-up resistor from FLG to either VIN or VOUT is required for proper operation. For information regarding the minimum and maximum values of pull-up resistance, refer to the graph in the “Typical Characteristics” section of the data sheet. Enable Input The MIC3775 features an active-high enable input (EN) that allows on-off control of the regulator. Current drain reduces to “zero” when the device is shutdown, with only microamperes of leakage current. The EN input has TTL/CMOS compatible thresholds for simple logic interfacing. EN may be directly tied to VIN and pulled up to the maximum supply voltage. Transient Response and 3.3V to 2.5V or 2.5V to 1.8V or 1.65V Conversion The MIC3775 has excellent transient response to variations in input voltage and load current. The device has been designed to respond quickly to load current variations and input voltage variations. Large output capacitors are not required to obtain this performance. A standard 10µF output capacitor, is all that is required. Larger values help to improve performance even further. By virtue of its low-dropout voltage, this device does not saturate into dropout as readily as similar NPN-based designs. When converting from 3.3V to 2.5V or 2.5V to 1.8V or 1.65V, the NPN-based regulators are already operating in dropout, with typical dropout requirements of 1.2V or greater. To convert down to 2.5V or 1.8V without operating in dropout, NPN-based regulators require an input voltage of 3.7V at the very least. The MIC3775 regulator will provide excellent performance |
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