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MIC5236-3.3BM Datasheet(PDF) 10 Page - Micrel Semiconductor |
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MIC5236-3.3BM Datasheet(HTML) 10 Page - Micrel Semiconductor |
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10 / 12 page  MIC5236 Micrel MIC5236 10 November 2000 COUT VOUT VIN 5V VERR IN MIC5236 EN 200k 1N4148 200k 4.7 µF OUT GND SHUTDOWN ENABLE ERR Figure 4. Remote Enable with Short-Circuit Current Foldback Thermal Characteristics The MIC5236 is a high input voltage device, intended to provide 150mA of continuous output current in two very small profile packages. The power SOP-8 and power MSOP-8 allow the device to dissipate about 50% more power than their standard equivalents. Power SOP-8 Thermal Characteristics One of the secrets of the MIC5236’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 package 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, θ JC (junction-to-case thermal resistance) and θ CA (case-to-ambi- ent thermal resistance). See Figure 5. θ JC is the resistance from the die to the leads of the package. θ CA is the resistance from the leads to the ambient air and it includes θ CS (case-to- sink thermal resistance) and θ SA (sink-to-ambient thermal resistance). θ JA θ JC θ CA printed circuit board ground plane heat sink area SOP-8 AMBIENT Figure 5. Thermal Resistance Using the power SOP-8 reduces the θ JC dramatically and allows the user to reduce θ CA. The total thermal resistance, θ JA (junction-to-ambient thermal resistance) is the limiting factor in calculating the maximum power dissipation capabil- ity of the device. Typically, the power SOP-8 has a θ JC of 20 °C/W, this is significantly lower than the standard SOP-8 which is typically 75 °C/W. θ CA is reduced because pins 5 through 8 can now be soldered directly to a ground plane which significantly reduces the case-to-sink thermal resis- tance 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 opera- tion of the device. To prevent this maximum junction tempera- ture from being exceeded, the appropriate ground plane heat sink must be used. 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) Figure 6. Copper Area vs. Power-SOP Power Dissipation (∆T JA) Figure 6 shows copper area versus power dissipation with each trace corresponding to a different temperature rise above ambient. From these curves, the minimum area of copper necessary for the part to operate safely can be determined. The maxi- mum allowable temperature rise must be calculated to deter- mine operation along which curve. ∆T = T J(max) – TA(max) T J(max) = 125°C T A(max) = maximum ambient operating temperature For example, the maximum ambient temperature is 50 °C, the ∆T is determined as follows: ∆T = 125°C – 50°C ∆T = 75°C Using Figure 6, the minimum amount of required copper can be determined based on the required power dissipation. Power dissipation in a linear regulator is calculated as fol- lows: P D = (VIN – VOUT) IOUT + VIN · IGND If we use a 3V output device and a 28V input at moderate output current of 25mA, then our power dissipation is as follows: P D = (28V – 3V) × 25mA + 28V × 250µA P D = 625mW + 7mW P D = 632mW From Figure 6, the minimum amount of copper required to operate this application at a ∆T of 75°C is 25mm2. Quick Method Determine the power dissipation requirements for the design along with the maximum ambient temperature at which the device will be operated. Refer to Figure 7, which shows safe operating curves for three different ambient temperatures: 25 °C, 50°C and 85°C. From these curves, the minimum |
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