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MIC5315-F4CYMT Datasheet(PDF) 9 Page - Micrel Semiconductor |
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MIC5315-F4CYMT Datasheet(HTML) 9 Page - Micrel Semiconductor |
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9 / 13 page  Micrel, Inc. MIC5315 July 2008 9 M9999-070208-A Application Information The MIC5315 is a high performance, dual low input voltage, ultra-low dropout regulator designed for low applications requiring very fast transient response. The MIC5315 utilizes two input supplies (VIN and VBIAS), significantly reducing the dropout voltage. The MIC5315 regulator is fully protected from damage due to fault conditions, offering linear current limiting and thermal shutdown. Bias Supply Voltage VBIAS, requiring relatively light current, provides power to the control portion of the MIC5315. Bypassing on the bias pin is recommended to improve performance of the regulator during line and load transients. A 1µF ceramic capacitor from VBIAS-to-ground is recommended to help reduce the high frequency noise from being injected into the control circuitry. Input Supply Voltage VIN1 and VIN2, provide the supply to power the LDOs independently. The minimum input voltage is 1.7V allowing conversion from low voltage supplies. The low input voltage provides high efficiency by reducing the input to output voltage step which minimizes the regulator power loss. Input Capacitor The MIC5315 is a high-performance, high bandwidth device. Therefore, it requires a well-bypassed input supply for optimal performance. A 1µF capacitor is required from the input-to-ground to provide stability. Low-ESR ceramic capacitors provide optimal performance at a minimum of space. Additional high- frequency capacitors, such as small-valued NPO dielectric-type capacitors, help filter out high-frequency noise and are good practice in any RF-based circuit. X5R or X7R dielectrics are recommended for the input capacitor. Y5V dielectrics lose most of their capacitance over temperature and are therefore, not recommended. Output Capacitor The MIC5315 requires an output capacitor of 1µF or greater to maintain stability. The design is optimized for use with low-ESR ceramic chip capacitors. High ESR capacitors may cause high frequency oscillation. The output capacitor can be increased, but performance has been optimized for a 1µF ceramic output capacitor and does not improve significantly with larger capacitance. 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. Bypass Capacitor A capacitor can be placed from the bypass pin-to-ground to reduce the output voltage noise. The capacitor bypasses the internal reference. A 0.01µF capacitor is recommended for applications that require low-noise outputs. The bypass capacitor can be increased, further reducing noise and improving PSRR. Turn-on time increases slightly with respect to the bypass capacitance. A unique, quick-start circuit allows the MIC5315 to drive a large capacitor on the bypass pin without significantly slowing turn-on time. No-Load Stability Unlike many other voltage regulators, the MIC5315 will remain stable and in regulation with no load. This is especially important in CMOS RAM keep-alive applications. Enable/Shutdown The MIC5315 is provided with dual active-high enable pins that allow each regulator to be disabled independently. Forcing the enable pin low 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. The active-high enable pin uses CMOS technology and the enable pin cannot be left floating; a floating enable pin may cause an indeterminate state on the output. Voltage Select The MIC5315 incorporates voltage select technology to set LDO2’s voltage output to a preset lower level. The /VSC2 pin is an active low input. A logic high signal sets VOUT2 to the full output voltage; while a logic low signal sets VOUT2 to the lower output voltage. Thermal Considerations The MIC5315 is designed to provide 300mA of continuous current for both outputs in a very small package. Maximum ambient operating temperature can be calculated based upon the output current and the voltage drop across the part. Given that the input voltage is 1.8V, the output voltage is 1.5V for VOUT1, 1.0V for VOUT2 and the output current = 300mA for each output. The actual power dissipation of the regulator circuit can be determined using the equation: PD = (VIN – VOUT1) IOUT1 + (VIN – VOUT2) I OUT2 + VBIAS IGND Because this device is CMOS and the ground current is |
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