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## MSK5251 Datasheet(PDF) 3 Page - M.S. Kennedy Corporation

 No. de Pieza. MSK5251 Descripción HIGH CURRENT, VERY LOW OUTPUT SURFACE MOUNT VOLTAGE REGULATORS Descarga 5 Pages Scroll/Zoom 100% Fabricante MSK [M.S. Kennedy Corporation] Página de inicio http://www.mskennedy.com Logo

## MSK5251 Datasheet(HTML) 3 Page - M.S. Kennedy Corporation

 3 / 5 page ]First, the power dissipation must be calculated as follows:Power Dissipation = (Vin - Vout) x Iout + Vin x Quiescent CurrentNext, the user must select a maximum junction tempera-ture. The equation may now be arranged to solve for therequired heat sink to ambient thermal resistance (Rθsa).EXAMPLE:An MSK 5251-1.3 is configured for Vin=+3.4V and Vout=+1.3V.Iout is a continuous 5Amp DC level. Under these conditions themaximum quiescent current would be 120mA. The ambient tempera-ture is +25°C and the maximum junction temperature is 125°C.Rθjc = 2.0°C/W and Rθcs = 0.5°C/W typically.Power Dissipation = (3.4V - 1.3V) x (5A + 3.4 x 120mA)Solve for Rθsa:Rθsa = 125°C - 25°C - 2.0°C/W - 0.5°C/WIn this example, a heat sink with a thermal resistance of nomore than 6.6°C/W must be used to maintain a junctiontemperature of no more than 125°C.APPLICATION NOTESREGULATOR PROTECTION:The MSK 5251 series are high performance linear regulators for highcurrent, low voltage applications requiring fast transient response.The devices are fully protected from damage due to fault conditions,offering constant current limiting and thermal shutdown. The thermalshutdown junction temperature is typically 140°C and is 100% testedto verify thermal shutdown occurs above 130°C.INPUT CAPACITOR:OUTPUT CAPACITOR:The MSK 5251 series devices require a minimum of external compo-nents to maintain stability. A minimum of output capacitance is nec-essary for stable operation. Due to the wide bandwidth design, thedevice will operate with a wide range of capacitance and ESR val-ues. For most applications, a 10uF ceramic capacitor will suffice.Ideally, this should be an X7R ceramic capacitor or a tantalum ca-pacitor due to their thermal performance. There is no upper limit tothe amount of output capacitance that may be used.INPUT SUPPLY VOLTAGE:The input voltage must be maintained at a minimum of 3.0 volts forproper operation for devices with output voltage below 1.0 volt.With an output voltage of 1.0 volt or higher, the input voltage mustbe a minimum of 2.1 volts above the output.31.7WPACKAGE CONNECTIONS:The MSK 5251 series are highly thermally conductive devices andthe thermal path from the package heat sink to the internal junctionsis very short. Standard surface mount soldering techniques should beused when mounting the device. Some applications may requireadditional heat sinking of the device.HEAT SINK SELECTION:To select a heat sink for the MSK 5251, the following for-mula for convective heat flow may be used:[= 6.67°C/WMINIMIZING POWER DISSIPATION:To maximize the performance and reduce power dissipation of theMSK 5251 series devices, Vin should be maintained as close todropout as possible. See Input Supply Voltage requirements. A seriesresistor can be used to lower Vin close to the dropout specification,lowering the input to output voltage differential. In turn, this willdecrease the power that the device is required to dissipate. Knowingpeak current requirements and worst case voltages, a resistor can beselected that will drop a portion of the excess voltage and help todistribute the heating. The circuit below illustrates this method.If the device is to be located more than 4 inches from the bulk supplycapacitance, a minimum 1uF capacitor should be placed as close tothe input pin as possible for proper bypassing. A smaller value ca-pacitor such as 0.01uF should be placed in parallel with the largervalue capacitor. Larger input capacitor values will help to improveripple rejection.The maximum resistor value can be calculated from the following:R1 max =Where: Vin min = Minimum input voltageVout max = Maximum output voltage across theVdrop = Worst case dropout voltage (Typically 2.1 Volts)Iout peak = Maximum load currentQuiescent Current = Max. quiescent current at Iout peakVin min - (Vout max + Vdrop)Iout peak + Quiescent Currentfull temperature rangeTHERMAL SHUTDOWN:The MSK 5251 series of devices is equipped with a thermal shut-down circuit that will turn off the device when the junction tempera-ture reaches approximately 140°C. It is important for the user to beaware that high temperature operation will limit the current capabil-ity of the device due to this thermal shutdown protection. In cases ofmaximum input voltage and high case temperature, the output cur-rent available may be less than 3 Amps. See curve below for clarifi-cation.= 10.9 WattsRev. D2/07