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MIC94325YMT Datasheet(PDF) 10 Page - Micrel Semiconductor |
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MIC94325YMT Datasheet(HTML) 10 Page - Micrel Semiconductor |
10 / 16 page Micrel, Inc. MIC94325/45/55 October 2012 10 M9999-102512-A Application Information The MIC943x5 family of products is a very-high PSRR, fixed-output, 500mA LDO utilizing Ripple Blocker technology. The MIC943x5 is fully protected from damage due to fault conditions, offering linear current limiting and thermal shutdown. Input Capacitor The MIC943x5 is a high-performance, high-bandwidth device. An input capacitor of 4.7µF 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 In order to maintain stability, the MIC943x5 requires an output capacitor of 4.7µF or greater. For optimal input voltage ripple rejection performance a 4.7µF capacitor is recommended. The design is optimized for use with low- ESR ceramic chip capacitors. High-ESR capacitors are not recommended because they may cause high- frequency oscillation. The output capacitor can be increased, but performance has been optimized for a 4.7µF 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 their value by as much as 50% and 60%, respectively, over their operating temperature ranges. To use a ceramic chip capacitor with the 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 MIC943x5 will remain stable and in regulation with no load. This is especially important in CMOS RAM keep-alive applications. Enable/Shutdown Forcing the enable (EN) pin low disables the MIC943x5 and sends it into a “zero” off mode current state. In this state, current consumed by the MIC943x5 goes nearly to zero. Forcing EN high enables the output voltage. The EN pin uses CMOS technology and cannot be left floating as it could cause an indeterminate state on the output. For the MIC94325 adjustable part, the turn-on time is affected by the selection of the external feedback resistors and feed-forward capacitor. The relationship is approximately 2.2 x R2 x Cff, where R2 is the bottom resistor (connected from ADJ to GND) and Cff is the capacitor connected across R1 (from VOUT to ADJ). For stability, the feed-forward capacitor must be greater than 1nF. 10nF is recommended for best performance. When disabled, the MIC94355 switches a 50Ω (typical) load on the regulator output to discharge the external capacitors. Adjustable Regulator Application The MIC94325 output voltage can be adjusted by using two external resistors (Figure 1). The resistors set the output voltage based on the following equation: R2 R1 1 V V ADJ OUT VADJ = 1.1V Figure 1. Adjustable Output Voltage Thermal Considerations The MIC943x5 is designed to provide 500mA of continuous current in a very-small package. Maximum ambient operating temperature can be calculated based on the output current and the voltage drop across the part. For example if the input voltage is 2.5V, the output voltage is 1.8V, and the output current = 500mA. The actual power dissipation of the Ripple Blocker™ can be determined using the equation: |
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