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MIC5321-3.3/2.9YD6 Datasheet(PDF) 9 Page - Micrel Semiconductor |
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MIC5321-3.3/2.9YD6 Datasheet(HTML) 9 Page - Micrel Semiconductor |
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9 / 12 page  Micrel, Inc. MIC5321 May 2008 9 M9999-051508-E Applications Information Enable/Shutdown The MIC5321 comes with a single active-high enable pin that allows both regulators to be disabled simultaneously. 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. Input Capacitor The MIC5321 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. Output Capacitor The MIC5321 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 perform- ance. 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 noise bypass pin to ground to reduce output voltage noise. The capacitor bypasses the internal reference. A 0.1µF 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 bypass capacitance. A unique, quick-start circuit allows the MIC5321 to drive a large capacitor on the bypass pin without significantly slowing turn-on time. Refer to the Typical Characteristics section for performance with different bypass capacitors. No-Load Stability Unlike many other voltage regulators, the MIC5321 will remain stable and in regulation with no load. This is especially important in CMOS RAM keep-alive applications. Thermal Considerations The MIC5321 is designed to provide 150mA of continuous current for both outputs in a very small package. Maximum ambient operating temperature can be calculated based on the output current and the voltage drop across the part. Given that the input voltage is 3.3V, the output voltage is 2.8V for VOUT1, 2.5V for VOUT2 and the output current = 150mA. The actual power dissipation of the regulator circuit can be determined using the equation: PD = (VIN – VOUT1) IOUT1 + (VIN – VOUT2) IOUT2+ VIN IGND Because this device is CMOS and the ground current is typically <150µA over the load range, the power dissipation contributed by the ground current is < 1% and can be ignored for this calculation. PD = (3.3V – 2.8V) × 150mA + (3.3V -1.5) × 150mA PD = 0.345W 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: PD(MAX) = TJ(MAX) - TA JA ⎝ ⎛ TJ(max) = 125°C, the maximum junction temperature of the die θJA thermal resistance = 100°C/W. The table below shows junction-to-ambient thermal resistance for the MIC5321 in the Thin MLF ® package. Package θJA Recommended Minimum Footprint θJC 6-Pin 1.6x1.6 Thin MLF ® 100°C/W 2°C/W Thermal Resistance |
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