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MIC39102YM Datasheet(PDF) 10 Page - Micrel Semiconductor |
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MIC39102YM Datasheet(HTML) 10 Page - Micrel Semiconductor |
10 / 12 page MIC39100/39101/39102 Micrel M9999-082505 10 August 2005 Adjustable Regulator Design IN R1 VOUT VIN COUT R2 EN OUT ADJ GND MIC39102 ENABLE SHUTDOWN V 1.240V 1 R1 R2 OUT = + Figure 2. Adjustable Regulator with Resistors The MIC39102 allows programming the output voltage any- where between 1.24V and the 16V maximum operating rating of the family. Two resistors are used. Resistors can be quite large, up to 1MΩ, because of the very high input impedance and low bias current of the sense comparator: The resistor values are calculated by: R1 R2 V 1.240 1 OUT = − Where VO is the desired output voltage. Figure 2 shows component definition. Applications with widely varying load currents may scale the resistors to draw the minimum load current required for proper operation (see above). Power SOIC-8 Thermal Characteristics One of the secrets of the MIC39101/2’s performance is its power SO-8 package featuring half the thermal resistance of a standard SO-8 package. Lower thermal resistance means more output current or higher input voltage for a given pack- age size. Lower thermal resistance is achieved by joining the four ground leads with the die attach paddle to create a single- piece electrical and thermal conductor. This concept has been used by MOSFET manufacturers for years, proving very reliable and cost effective for the user. Thermal resistance consists of two main elements, θJC (junc- tion-to-case thermal resistance) and θCA (case-to-ambient thermal resistance). See Figure 3. θJC is the resistance from the die to the leads of the package. θCA is the resistance from the leads to the ambient air and it includes θCS (case- to-sink thermal resistance) and θSA(sink-to-ambient thermal resistance). Using the power SOIC-8 reduces the θJC dramatically and allows the user to reduce θCA. The total thermal resistance, θJA (junction-to-ambient thermal resistance) is the limiting factor in calculating the maximum power dissipation capabil- ity of the device. Typically, the power SOIC-8 has a θJC of 20°C/W, this is significantly lower than the standard SOIC-8 which is typically 75°C/W. θCA is reduced because pins 5 through 8 can now be soldered directly to a ground plane whichsignificantlyreducesthecase-to-sinkthermalresistance and sink to ambient thermal resistance. Low-dropout linear regulators from Micrel are rated to a maximum junction temperature of 125°C. It is important not to exceed this maximum junction temperature during operation of the device. To prevent this maximum junction temperature from being exceeded, the appropriate ground plane heat sink must be used. JA JC CA printed circuit board ground plane heat sink area SOIC-8 AMBIENT Figure 3. Thermal Resistance Figure 4 shows copper area versus power dissipation with each trace corresponding to a different temperature rise above ambient. Fromthesecurves,theminimumareaofcoppernecessaryfor the part to operate safely can be determined. The maximum allowable temperature rise must be calculated to determine operation along which curve. 0 100 200 300 400 500 600 700 800 900 0 0.25 0.50 0.75 1.00 1.25 1.50 POWER DISSIPATION (W) ∆T J A = Figure 4. Copper Area vs. Power-SOIC Power Dissipation 0 100 200 300 400 500 600 700 800 900 0 0.25 0.50 0.75 1.00 1.25 1.50 POWER DISSIPATION (W) T A = 85°C 50°C 25°C T J = 125°C Figure 5. Copper Area vs. Power-SOIC Power Dissipation |
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