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MSK5200-HZS Datasheet(PDF) 3 Page - M.S. Kennedy Corporation |
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MSK5200-HZS Datasheet(HTML) 3 Page - M.S. Kennedy Corporation |
3 / 5 page APPLICATION NOTES HEAT SINKING: To determine if a heat sink is required for your application and if so, what type, refer to the thermal model and governing equation below. Governing Equation: Tj = Pd x (Rθjc + Rθcs + Rθsa) + Ta WHERE Tj = Junction Temperature Pd = Total Power Dissipation Rθj = Junction to Case Thermal Resistance Rθcs = Case to Heat Sink Thermal Resistance Rθsa = Heat Sink to Ambient Thermal Resistance Tc = Case Temperature Ta = Ambient Temperature Ts = Heat Sink Temperature EXAMPLE: This example demonstrates an analysis where each regulator is at one-half of its maximum rated power dissipation, which oc- curs when the output currents are at 1.5 amps each. The nega- tive regulator is worst case due to the larger thermal resis- tance. Conditions for MSK 5202: Vin = ±7.0V; Iout = ±1.5A 1.) Assume 45° heat spreading model. 2.) Find regulator power dissipation: Pd = (Vin - Vout)(Iout) Pd = (7-5)(1.5) Pd = 3.0W 3.) For conservative design, set Tj = +125°C Max. 4.) For this example, worst case Ta = +90°C. 5.) Rθjc = 4.7°C/W from the Electrical Specification Table. 6.) Rθcs = 0.15°C/W for most thermal greases. 7.) Rearrange governing equation to solve for Rθsa: Rθsa= ((Tj - Ta)/Pd) - (Rθjc) - (Rθcs) = (125°C - 90°C)/3.0W - (4.7°C/W) - ( 0.15°C/W) = 6.8°C/W The same exercise must be performed for the negative regula- tor. In this case the result is 6.82°C/W. Therefore, a heat sink with a thermal resistance of no more than 6.8°C/W must be used in this application to maintain both regulator circuit junc- tion temperatures under 125°C. OVERLOAD SHUTDOWN: The regulators feature both current and thermal overload protection. When the maximum power dissipation is not ex- ceeded, the regulators will current limit slightly above their 3 amp rating. As the Vin-Vout voltage increases, however, shut- down occurs in relation to the maximum power dissipation curve. If the device heats enough to exceed its rated die junction tem- perature due to excessive ambient temperature, improper heat sinking etc., the regulators also shutdown until an appropriate junction temperature is maintained. It should also be noted that in the case of an extreme overload, such as a sustained direct short, the device may not be able to recover. In these instances, the device must be shut off and power reapplied to eliminate the shutdown condition. LOAD REGULATION: For best results the ground pin should be connected directly to the load as shown below. This effectively reduces the ground loop effect and eliminates excessive voltage drop in the sense leg. It is also important to keep the output connection between the regulator and the load as short as possible since this di- rectly affects the load regulation. If 20 gauge wire were used as an example, which has a resistance of about .008 ohms per foot, this would result in a drop of 8mV/ft at 1Amp of load current. It is also important to follow the capacitor selection guidelines to achieve best performance. Refer to Figure 2 for connection diagram. FIGURE 2 Avoiding Ground Loops BYPASS CAPACITORS: For most applications a 47uF, tantalum capacitor should be attached as close to the regulator's output as possible. This will effectively lower the regulator's output impedance, improve transient response and eliminate any oscillations that may be normally associated with low dropout regulators. Additional bypass capacitors can be used at the remote load locations to further improve regulation. These can be either of the tantalum or the electrolytic variety. Unless the regulator is located very close to the power supply filter capacitor(s), a 4.7uF minimum tantalum capacitor should also be added to the regulator's in- put. An electrolytic may also be substituted if desired. When substituting electrolytic in place of tantalum capacitors, a good rule of thumb to follow is to increase the size of the electrolytic by a factor of 10 over the tantalum value. Low Dropout Positive and Negative Power Supply MSK 5202 TYPICAL APPLICATION: FIGURE 1 3 Rev. F 11/04 |
Similar Part No. - MSK5200-HZS |
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Similar Description - MSK5200-HZS |
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