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MIC5209-2.5BS Datasheet(PDF) 10 Page - Micrel Semiconductor |
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MIC5209-2.5BS Datasheet(HTML) 10 Page - Micrel Semiconductor |
10 / 13 page MIC5209 Micrel, Inc. M9999-060906 10 June 2006 Fixed Regulator Circuits MIC5209-x.xBM IIN N OUT OUT GND 1µF VIN VOUT EN BYP 1 2 5–8 3 4 Figure 1. Low-Noise Fixed Voltage Regulator Figure 1 shows a basic MIC5209-x.xBM (SO-8) fixed-voltage regulator circuit. See Figure 5 for a similar configuration us- ing the more thermally-efficient MIC5209-x.xBS (SOT-223). A 1µF minimum output capacitor is required for basic fixed- voltage applications. MIC5209-x.xBM IIN N OUT OUT GND 470pF VIN EEN N BYP BYP 1 2 5–8 3 4 2.2µF VOUT Figure 2. Ultra-Low-Noise Fixed Voltage Regulator Figure 2 includes the optional 470pF noise bypass capacitor between BYP and GND to reduce output noise. Note that the minimum value of COUT must be increased when the bypass capacitor is used. Adjustable Regulator Circuits MIC5209BM IIN N OUT OUT GND VIN EEN N ADJ ADJ 1 2 5–8 3 4 1µF VOUT R1 R2 Figure 3. Low-Noise Adjustable Voltage Regulator The MIC5209BM/U can be adjusted to a specific output volt- age by using two external resistors (Figure 3). The resistors set the output voltage based on the equation: V = 1.242V + R2 R1 OUT V V 1 This equation is correct due to the configuration of the bandgap reference. The bandgap voltage is relative to the output, as seen in the block diagram. Traditional regula- tors normally have the reference voltage relative to ground; therefore, their equations are different from the equation for the MIC5209BM/U. AlthoughADJisahigh-impedanceinput,forbestperformance, R2 should not exceed 470kΩ. MIC5209BM IN OUT GND VIN EN ADJ 1 2 5–8 3 4 2.2µF VOUT R1 R2 470pF Figure 4. Ultra-Low-Noise Adjustable Application. Figure 4 includes the optional 470pF bypass capacitor from ADJ to GND to reduce output noise. Slot-1 Power Supply Intel’s Pentium II processors have a requirement for a 2.5V ±5% power supply for a clock synthesizer and its associated loads. The current requirement for the 2.5V supply is depen- dant upon the clock synthesizer used, the number of clock outputs, and the type of level shifter (from core logic levels to 2.5V levels). Intel estimates a worst-case load of 320mA. The MIC5209 was designed to provide the 2.5V power requirement for Slot-1 applications. Its guaranteed perfor- mance of 2.5V ±3% at 500mA allows adequate margin for all systems, and its dropout voltage of 500mV means that it operates from a worst-case 3.3V supply where the voltage can be as low as 3.0V. MIC5209-x.xBS IIN N OUT OUT GND COUT 22µF VIN VOUT 1 2,TAB 3 CIN 0.1µF Figure 5. Slot-1 Power Supply A Slot-1 power supply (Figure 5) is easy to implement. Only two capacitors are necessary, and their values are not criti- cal. CIN bypasses the internal circuitry and should be at least 0.1µF. COUT provides output filtering, improves transient response, and compensates the internal regulator control loop. Its value should be at least 22µF. CIN and COUT may be increased as much as desired. Slot-1 Power Supply Power Dissipation Powered from a 3.3V supply, the Slot-1 power supply of Figure 5 has a nominal efficiency of 75%. At the maximum anticipated Slot 1 load (320mA), the nominal power dissipa- tion is only 256mW. The SOT-223 package has sufficient thermal characteristics for wide design margins when mounted on a single layer copper-clad printed circuit board. The power dissipation of the MIC5209 is calculated using the voltage drop across the device × output current plus supply voltage × ground current. |
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