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MIC5338-4CYMT Datasheet(PDF) 8 Page - Micrel Semiconductor |
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MIC5338-4CYMT Datasheet(HTML) 8 Page - Micrel Semiconductor |
8 / 12 page Micrel, Inc. MIC5338/9 June 2010 8 M9999-063010-A Application Information MIC5338/9 is a dual 300mA LDO. The MIC5339 includes an auto-discharge circuit for each LDO output that is activated when the output is disabled. The MIC5338/9 regulator is fully protected from damage due to fault conditions through linear current limiting and thermal shutdown. Input Capacitor The MIC5338/9 is a high performance, high bandwidth device. An input capacitor of 1µF from the input pin to ground is required to provide stability. Low ESR ceramic capacitors provide optimal performance in small board area. 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 MIC5338/9 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 and X5R dielectric ceramic capacitors are recommended because of their temperature performance. X7R 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 MIC5338/9 will remain stable and in regulation with no load. Enable/Shutdown The MIC5338/9 comes with two active high enable pins that allow each regulator to be disabled independently. Forcing the enable pin low disables the regulator and sends it into an off mode current state drawing virtually zero current. When disabled, the MIC5339 switches an internal 30Ω load on the regulator output to discharge the external capacitor. Forcing the enable pin high enables the output voltage. The active high enable pin uses CMOS technology and cannot be left floating. A floating enable pin may cause an indeterminate state on the output. Thermal Considerations The MIC5338/9 is designed to provide two 300mA continuous current outputs in a very small package. Maximum operating temperature can be calculated based on the output currents and the voltage drop across the part. For example, if the input voltage is 3.6V, VOUT1 = 3.3V, VOUT2 = 2.8V and each with an output current = 300mA. The actual power dissipation of the regulator circuit can be determined using the equation: PD = (VIN – VOUT1) IOUT1 + (VIN – VOUT2) I OUT2 + VIN IGND Because this is CMOS device and the ground current is typically <100µA over the load range, the power dissipation contributed by the ground current is < 1% which can be ignored for this calculation. PD = (3.6V – 3.3V) × 300mA + (3.6V – 2.8V) × 300mA PD = 0.33W 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 A J(MAX) D(MAX) θ T T P TJ(MAX) = 125°C θJA = 92.4°C/W Substituting PD for PD(MAX) and solving for the ambient operating temperature will give the maximum operating conditions for the regulator circuit. The junction to ambient thermal resistance for the minimum footprint is 92.4°C/W. The maximum power dissipation must not be exceeded for proper operation. |
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