MIC5365/6: High Performance Single 150mA LDO - Micrel - #9

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Micrel, Inc. MIC5365/6 September 2009 9 M9999-090109-C Application Information MIC5365 and MIC5366 are Low noise 150mA LDOs. The MIC5366 includes an auto-discharge circuit that is switched on when the regulator is disabled through the Enable pin. The MIC5365/6 regulator is fully protected from damage due to fault conditions, offering linear current limiting and thermal shutdown. Input Capacitor The MIC5365/6 is a high-performance, high bandwidth device. An input capacitor of 1ìF 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 MIC5365/6 requires an output capacitor of 1ìF or greater to maintain stability. 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 1ìF 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. No-Load Stability Unlike many other voltage regulators, the MIC5365/6 will remain stable and in regulation with no load. This is especially important in CMOS RAM keep-alive applications. Enable/Shutdown The MIC5365/6 comes with an active-high enable pin that allows the regulator to be disabled. 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. Thermal Considerations The MIC5365/6 is designed to provide 150mA 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 3.6V, the output voltage is 2.8V, and the output current = 150mA. The actual power dissipation of the regulator circuit can be determined using the equation: PD = (VIN – VOUT1) I OUT + VIN IGND Because this device is CMOS and the ground current is typically <100ìA over the load range, the power dissipation contributed by the ground current is < 1% and can be ignored for this calculation. PD = (3.6V – 2.8V) × 150mA PD = 0.120W To determine the maximum ambient operating temperature of the package, use the junction-to-ambient thermal resistance of the device and the following basic equation: . . . . - = JA J(max) A D(max) T T P è TJ(max) = 125°C, the maximum junction temperature of the die, èJA thermal resistance = 250°C/W for the YMT package and 256.5°C/W for the SC-70-5 package. Substituting PD for PD(max) and solving for the ambient operating temperature will give the maximum operating conditions for the regulator circuit. The junction-toambient thermal resistance for the minimum footprint is 250°C/W. The maximum power dissipation must not be exceeded for proper operation.