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MIC2215-PPGYML Datasheet(PDF) 9 Page - Micrel Semiconductor |
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MIC2215-PPGYML Datasheet(HTML) 9 Page - Micrel Semiconductor |
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9 / 11 page  Micrel, Inc. MIC2215 January 2007 9 M9999-011207 Application Information Enable/Shutdown The MIC2215 comes with three active-high enable pins that allow control of each individual regulator to be either disabled or enabled. Forcing the enable pin low disables the respective regulator and sends it into a “zero” off- mode-current state. In this state, current consumed by the individual regulator goes nearly to zero. This is true for both regulators 2 and 3. Regulator 1’s input supply pin is also used to power the internal reference. When any regulator; either 1, 2, or 3 is enabled, an additional 20µA for the reference will be drawn through VIN1. All three must be disabled to enter the “zero” current-off- mode-state. Forcing the enable pin high enables each respective output voltage. This part is CMOS and none of the enable pins can be left floating; a floating enable pin may cause an indeterminate state on the output. Input Capacitor The MIC2215 is a high performance, high bandwidth device. Therefore, it requires a well-bypassed input supply for optimal performance. A small 0.1µF capacitor placed close to the input is recommended to aid in noise performance. Low-ESR ceramic capacitors provide opti- mal performance at a mini-mum of space. Additional high-frequency capacitors such as small valued NPO dielectric type capacitors help to filter out high frequency noise and are good practice in any RF-based circuit. Output Capacitor The MIC2215 requires an output capacitor for stability. The design requires 1µF or greater on the output to maintain stability. The design is optimized for use with low-ESR ceramic chip capacitors. X7R/X5R dielectric- type ceramic capacitors are recommended because of their temperature performance. X7R-type capacitors change capacitance by 15% over their operating temp- erature 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 Pin A capacitor can be placed from the noise bypass pin to ground to reduce output voltage noise. The capacitor bypasses the internal reference. There is one single internal reference shared by each output, therefore the bypassing affects each regulator. 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. Internal Reference The internal band gap, or reference, is powered from the VIN1 input. Due to some of the input noise (PSRR) contributions being imposed on the band gap, it is important to make V IN1 as clean as possible with good bypassing close to the input. Multiple Input Supplies The MIC2215 can be used with multiple input supplies when desired. The only requirement, aside from maintaining the voltages within the operating ranges, is that VIN1 always remains the highest voltage potential. No-Load Stability The MIC2215 will remain stable and in regulation with no load, unlike many other voltage regulators. This is especially important in CMOS RAM keep-alive app- lications. Thermal Considerations The MIC2215 is designed to provide up to 250mA of current per channel in a very small package. Maximum power dissipation can be calculated based on the output current and the voltage drop across the part. To determine the maximum power dissipation of the package, use the junction-to-ambient thermal resistance of the device and the following basic equation: PD(max) = (TJ(max) – TA)÷θJA TJ(max) is the maximum junction temperature of the die, 125°C, and TA is the ambient operating temperature. θJA is layout dependent; Table 2 shows examples of the junction-to-ambient thermal resistance for the MIC2215. Package θJA Recommended Minimum Footprint 16-Pin 4mm x 4mm MLF ® 43°C/W Table 2. MLF ® Thermal Resistance The actual power dissipation of the regulator circuit can be determined using the equation: PDTOTAL = PDLDO1 + PDLDO2 + PDLDO3 PDLDO1 = (VIN1 – VOUT1) × IOUT1 PDLDO2 = (VIN2 – VOUT2) × IOUT2 PDLDO3 = (VIN3 – VOUT3) × IOUT3 Substituting PD (max) for PD and solving for the operating conditions that are critical to the application will give the maximum operating conditions for the regulator circuit. For example, when operating the MIC2215 at 60°C with a minimum footprint layout, the maximum load currents can be calculated as follows: PD (max) = (125°C – 60°C)/43 °C/W PD (max) = 1.511W |
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