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MIC5216-3.6YM5 Datasheet(PDF) 9 Page - Micrel Semiconductor |
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MIC5216-3.6YM5 Datasheet(HTML) 9 Page - Micrel Semiconductor |
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9 / 13 page  Micrel, Inc. MIC5216 March 2007 9 M9999-032307 VIN = 6.2VMAX Therefore, a 3.3V application at 150mA of output current can accept a maximum input voltage of 6.2V in a SOT- 23-5 package. For a full discussion of heat sinking and thermal effects on voltage regulators, refer to the Regulator Thermals section of Micrel’s Designing with Low-Dropout Voltage Regulators handbook. Peak Current Applications The MIC5216 is designed for applications where high start-up currents are demanded from space constrained regulators. This device will deliver 500mA start-up current from a SOT-23-5 or MM8 package, allowing high power from a very low profile device. The MIC5216 can subsequently provide output current that is only limited by the thermal characteristics of the device. You can obtain higher continuous currents from the device with the proper design. This is easily proved with some thermal calculations. If we look at a specific example, it may be easier to follow. The MIC5216 can be used to provide up to 500mA continuous output current. First, calculate the maximum power dissipation of the device, as was done in the thermal considerations section. Worst case thermal resistance (θJA = 220°C/W for the MIC5216- x.xBM5), will be used for this example. ( ) JA A J(MAX) D(MAX) θ T T P − = Assuming room temperature, we have a maximum power dissipation number of () C/W 220 C 25 C 125 PD(MAX) ° ° − ° = PD(MAX) = 455mW Then we can determine the maximum input voltage for a five-volt regulator operating at 500mA, using worst case ground current. PD(MAX) = 455mW = (VIN – VOUT) IOUT + VIN IGND IOUT = 500mA VOUT = 5V IGND =20mA 455mW = (VIN – 5V) 500mA + VIN × 20mA 2.995mW = 520mA × VIN 5.683V 520mA 2.955W VIN(MAX) = = Therefore, to be able to obtain a constant 500mA output current from the 5216-5.0BM5 at room temperature, you need extremely tight input-output voltage differential, barely above the maximum dropout voltage for that current rating. You can run the part from larger supply voltages if the proper precautions are taken. Varying the duty cycle using the enable pin can increase the power dissipation of the device by maintaining a lower average power figure. This is ideal for applications where high current is only needed in short bursts. Figure 1 shows the safe operating regions for the MIC5216-x.xBM5 at three different ambient temperatures and at different output currents. The data used to determine this figure assumed a minimum footprint PCB design for minimum heat sinking. Figure 2 incorporates the same factors as the first figure, but assumes a much better heat sink. A 1” square copper trace on the PC board reduces the thermal resistance of the device. This improved thermal resistance improves power dissipation and allows for a larger safe operating region. Figures 3 and 4 show, safe operating regions for the MIC5216-x.xBMM, the power MSOP package part. These graphs show three typical operating regions at different temperatures. The lower the temperature, the larger the operating region. The graphs were obtained in a similar way to the graphs for the MIC5216-x.xBM5, taking all factors into consideration and using two different board layouts, minimum footprint and 1” square copper PC board heat sink. (For further discussion of PC board heat sink characteristics, refer to Application Hint 17, “Designing PC Board Heat Sinks”. The information used to determine the safe operating regions can be obtained in a similar manner to that used in determining typical power dissipation, already discussed. Determining the maximum power dissipation based on the layout is the first step, this is done in the same manner as in the previous two sections. Then, a larger power dissipation number multiplied by a set maximum duty cycle would give that maximum power dissipation number for the layout. This is best shown through an example. If the application calls for 5V at 500mA for short pulses, but the only supply voltage available is 8V, then the duty cycle has to be adjusted to determine an average power that does not exceed the maximum power dissipation for the layout. () GND IN OUT OUT IN D I V I V V 100 %DC Avg.P + − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ = () 20mA V 8 500mA V 5 8V 100 %DC 455mW × + − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ = |
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