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AHP2812SZHB Datasheet(PDF) 7 Page - International Rectifier |
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AHP2812SZHB Datasheet(HTML) 7 Page - International Rectifier |
7 / 12 page www.irf.com 7 AHP270XXS Series minor variations of either surface. While other available types of heat conductive materials and compounds may provide similar performance, these alternatives are often less convinient and are frequently messy to use. A conservative aid to estimating the total heat sink surface area (AHEAT SINK) required to set the maximum case temperature rise ( ∆T) above ambient temperature is given by the following expression: A HEAT SINK ≈ ⎧ ⎨ ⎩ ⎫ ⎬ ⎭ − − ∆T P 80 30 085 143 . . . where ∆T PP Eff OUT = == − ⎧ ⎨ ⎩ ⎫ ⎬ ⎭ Case temperature rise above ambient Device dissipation in Watts 1 1 ∆T = 85 - 25 = 60°C () P =• − ⎧ ⎨ ⎩ ⎫ ⎬ ⎭ =• = 120 1 83 1 120 0 205 24 6 . .. W and the required heat sink area is A = 60 80 24.6 in HEAT SINK 0.85 • ⎧ ⎨ ⎩ ⎫ ⎬ ⎭ −= −143 2 30 71 . . From the Specification Table, the worst case full load efficiency for this device is 83%; therefore the power dissipation at full load is given by Because of the incorporation of many innovative technological concepts, the AHP series of converters is capable of providing very high output power from a package of very small volume. These magnitudes of power density can only be obtained by combining high circuit efficiency with effective methods of heat removal from the die junctions. This requirement has been effectively addressed inside the device; but when operating at maximum loads, a significant amount of heat will be generated and this heat must be conducted away from the case. To maintain the case temperature at or below the specified maximum of 125°C, this heat must be transferred by conduction to an appropriate heat dissipater held in intimate contact with the converter base-plate. Because effectiveness of this heat transfer is dependent on the intimacy of the baseplate/heatsink interface, it is strongly recommended that a high thermal conductivity heat transferance medium is inserted between the baseplate and heatsink. The material most frequently utilized at the factory during all testing and burn-in processes is sold under the trade name of Sil-Pad ® 4001 . This particular pro duct is an insulator but electrically conductive versions are also available. Use of these materials assures maximum surface contact with the heat dissipator thereby compensating for When operating in the shared mode, it is important that symmetry of connection be maintained as an assurance of optimum load sharing performance. Thus, converter outputs should be connected to the load with equal lengths of wire of the same gauge and sense leads from each converter should be connected to a common physical point, preferably at the load along with the converter output and return leads. All converters in a paralleled set must have their share pins connected together. This arrangement is diagrammatically illustrated in Figure III. showing the outputs and sense pins connected at a star point which is located as close as possible to the load. As a consequence of the topology utilized in the current sharing circuit, the share pin may be used for other functions. In applications requiring a single converter, the voltage appearing on the share pin may be used as a “current monitor”. The share pin open circuit voltage is nominally +1.00V at no load and increases linearly with increasing output current to +2.20V at full load. The share pin voltage is referenced to the output return pin. Thus, a total heat sink surface area (including fins, if any) of 71 in2 in this example, would limit case rise to 60°C above ambient. A flat aluminum plate, 0.25" thick and of approximate dimension 4" by 9" (36 in2 per side) would suffice for this application in a still air environment. Note that to meet the criteria in this example, both sides of the plate require unrestricted exposure to the ambient air. 1Sil-Pad is a registered Trade Mark of Bergquist, Minneapolis, MN As an example, it is desired to maintain the case temperature of an AHP27015S at ≤ +85°C in an area where the ambient temperature is held at a constant +25°C; then Thermal Considerations |
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