HSK-VSX中文资料

Application GuideDCAN-40Rev FVSX60&VSX75APPLICATION NOTESBy Barry Ehrman,Applications EngineerThe VSX60Series and VSX75Series are60Watt and75Watt,respectively,dual output converters with18-36V(VSX60only)and36-75V input models with3.3VDC and5VDC outputs.The VSX60and VSX75converters are packaged in the industry quarter-pak size of1.5”x 2.3”x0.5”and have a typical efficiency of90%.The following application information is designed to supplement the product data sheet.Additional Information On The Control FeaturesRemote On/Off ControlThe VSX60Series and VSX75Series are equipped with a primary on/off control pin for increased system flexibility.The input is TTL open-collector and/or CMOS open-drain compatible.On the standard model,the primary on/off pin uses negative logic,which turns the converter ON when a logic low signal is applied(see common specifications for threshold voltage levels).Figure1illustrates the typical external connections to enable this function.If no connection is made to the primary on/off terminal,the converter will not operate.Figure1:Primary On/Off ConnectionsIn addition there is“-1”option for the VSX60Series and VSX75Series(i.e.VSX60MD35-1)which allows the converters to operate on positive logic.The recommended control circuits would be the same as Figure1except the input logic would be reversed(i.e.input logic low will turn off the converter and input logic high will turn on the converter).If no connection is made to the primary on/off terminal of the converter with the“-1”option,the converter will operate normally.Output Voltage TrimThe output voltage trim feature allows the user to accurately adjust the converter's output voltage set point to a specified level(see Table1).This is achieved by connecting a resistor from the TRIM terminal to either the3V3(+3.3Volt Output)or O/P RTN(Output Return)pins.If an increased output voltage is desired,the resistor should be connected between the TRIM and O/P RTN pins.If a decreased output voltage is desired,the external resistor should be connected between the TRIM and3V3pins.Figure2 illustrates the required connections to implement this feature.Connecting the TRIM pin directly to the3V3pin will trim the converter down10%and connecting the TRIM pin directly to the O/P RTN pin will trim the converter up10%.Please Note:When using theoutput voltage“Trim”feature,both outputs will be adjusted in the same direction and by the same percentage.TABLE 1 -) VALUES (KOHMS) FOR DESIRED INCREASE IN OUTPUT VOLTAGE (%)RESISTOR (RUPMODEL12345678910 VSX60xS3550.32723.21113.9069.202 6.363 4.463 3.102 2.08 1.2840 ) VALUES (KOHMS) FOR DESIRED DECREASE IN OUTPUT VOLTAGE (%)RESISTOR (RDOWNMODEL12345678910 VSX60xS3567.11629.51217.35811.357.767 5.388 3.692 2.423 1.4380Design ConsiderationsCurrent LimitingEach converter is equipped with current-limiting circuitry designed to provide continuous protection against fault or short circuit conditions.The current limit point is typically5%-25%above the rated output current.When the short circuit condition is removed,the output voltage will return to its”pre-short circuit”value without recycling the input.SafetyThe VSX60Series and VSX75Series are recognized to be in conformance with UL/CUL1950and EN60950.The output of the VSX60and VSX75are considered to be a level3output when the supply to the converter meets SELV requirements(VIN<60VDC).Fusing RequirementsThe VSX60Series and VSX75Series converters are not internally fused.In order to maintain maximum safety and overall system protection,an input line fuse should always be included.A normal blow D.C. fuse with a maximum rating of6A is recommended.Input Source ImpedanceThe converter should be connected to a low AC impedance input source to ensure system stability.It is recommended that a small electrolytic capacitor with a low ESR(eg.33µF,0.5Ω)for48V input models (M),330µF,0.14Ωfor24V input models(L))should be placed across the input terminals as close to the module as possible to maintain unit stability.Test Circuit ConfigurationsFigure3:Measurement of Input Reflected RippleFigure4:Measurement of Input Reflected Ripple with External Reduction CircuitFigure 5: Measurement of Peak to Peak Output NoiseCircuit Configuration Designed to Minimize Conducted EMIMinimizing conducted EMI from a switching DC to DC converter can sometimes be a challenge. The VSX60 and VSX75 EMI filter circuit shown in Figure 6 and the circuit layout in Figure 7 was designed to simplify this challenge. This circuit can be used in most applications with little or no modification to meet most FCC requirements.Figure 6: VSX EMI Filter CircuitFigure 7: Circuit Layout For VSX EMI FilterThe following components are recommended for the Circuit in Figures 6 and 7 F1 6 Amp Normal Blow FuseC10.68 µF Metallized Polyester Film CapacitorsC2, C31000 pF Ceramic Type 1500V CapacitorsC5, C6 4.7 nF 1500 Volt Ceramic CapacitorsC7, C8, C9, C100.1 µF 200 Volt Ceramic Type CapacitorsC11, C120.1 µF 200 Volt Ceramic Type CapacitorsC433 µF, 100 Volt Low ESR, Electrolytic CapacitorL1Common-mode Inductor, Pulse P0351 or equivalentR1, R2 5 Ohm surface mount resistors (application dependent)Figure 8 are actual graphs from a spectrum analyzer showing the conducted EMI from a fully loaded VSX60MS35 when used in conjunction with the recommended board layout and suggested components. The limit lines in the graphs are CISPR Class B, Quasi Peak emission limits.Figure 8: VSX60 Conducted EMI Using Recommended Board Layout and Components Thermal ConsiderationsThe VSX60Series and VSX75Series of products are designed to operate with a baseplate temperature between-40degrees C.and+100degrees C.If the baseplate temperature should rise above+100degrees due to internal heat generation,an Over Temperature Protection(OTP)circuit will turn the VSX converter off to prevent any damage.The unit will turn itself back on when the baseplate temperature drops below100degrees C.The actual OTP shutdown temperature is between110and125degrees C.case.To avoidunexpected shutdown,it is important to always keep the baseplate temperature below100 degrees C.This can be done by first calculating the case temperature under the worst case conditions and determine if additional airflow,a heatsink or both maybe required. Thermal EquationsIn order to calculate the case temperature in a particular application, the following thermal equations will prove useful:1) Efficiency = η = P OUT / P IN(P= Power)2) Dissipated Power (Power Lost) = P D = P OUT {(1-η)/η}3) Temperature Rise = P D x θBA = P OUT x θBA {(1-η)/η}(θBA =Thermal Resistance from Base to Ambient)4)Maximum Output Power= {T BASE (max) - T A} /[θBA{(1-η)/η}(T BASE (max) = Maximum BaseTemperature = 100 degrees C)(T A = Ambient Temperature)5) Minimum Thermal Impedance = {T bASE (max) - T A}/[P OUT{(1-η)/η}Normalized Efficiency ChartsThe following charts can be used to more precisely predict the expected efficiency of the VSX60and VSX75:Thermal ImpedanceVSX THERMAL IMPEDANCE WITHOUT A HEATSINK θBA(Degree C / Watt) Air Flow LFM Without Mechanical Tie With Mechanical Tie Down** Free Air12.210.372007.49 6.963007.05 6.58400 6.24 6.19500 5.79 5.78600 5.53 5.48700 5.20 5.18**Mechanically tied down through (4) PEMS with steel screws to a 2 layer FR4. FR4 Top ground plane contains 11.75 sq. in. of 2 oz copper and FR4 ground plane contains 16 sq. in of 2 oz. copper. The steel screws shall be applied from the baseplate side of the converter and a nut and washer shall be used to make the electrical connection to the FR4 ground plane. Applying the screws from the FR4 side of the converter will void the converter’s warranty.The following example will illustrate how to calculate the baseplate temperature under specific operating conditions:Example:A customer has an application that requires a VSX60MD35to drive a load of53watts in a cabinet at50degrees C.with200linear feet per minute of air flow.The input voltage will be typically48Volts but under some conditions may rise to52Volts.The load current on theVSX60MD35will be distributed between the5Volt output and3.3Volt output as follows:5.0Volt load current=4Amps3.3Volt load current=10AmpsIn order to determine the baseplate temperature of the VSX60MD35,the amount of heat generated must be determined.Heat generated by converter caused by the inefficiency of the converter iscalled“Dissipated Power”.The efficiency of the VSX60MD35with a53Watt load,under the stated conditions,can be calculated as follows:Efficiency=η=ηpds xηvin xηtld xηldd=(.89)x(.997)x(1.00)x(.996)=88.38%Where:ηpds=Minimum Efficiency of VSX60MD35from data sheet=89%ηvin=Efficiency adjustment factor based on the graph of Normalized Efficiency Vs.InputVoltageηtld=Efficiency adjustment factor based on the graph of Normalized Efficiency Vs.Total Output Load ηldd=Efficiency adjustment factor based on the graph of Normalized Efficiency Vs.Load Distribution Because efficiency is defined as Power-Out(P OUT)divided by Power-In(P IN)times100%,the Dissipated Power(P D)can be calculated as follows:Efficiency/100% = η =POUT /PIN= (V OUT x I OUT)/(V IN x I IN)Dissipated Power = PD =POUT{(1-η)/η} = 53 x{(1-0.8838)/0.8838}Dissipated Power=6.968WattsNext,the temperature rise of the baseplate can be determined by multiplying the thermal resistance from base plate to ambient(θBA)which can be found in the Thermal Impedance chart on page8 times the Dissipated Power.By knowing the temperature rise of the baseplate,the worst case temperature of the baseplate can be determined by adding the ambient temperature T A which is shown as follows:Temperature Rise=T R=PD xθBA=POUTxθBA{(1-η)/η}=6.968x7.49=52.19degrees C.Temperature of the baseplate=T BP=T R x T A=52.19+50=102.19degrees C.With a baseplate temperature of102.19degrees C.,the converter will operate outside of its specified temperature range.There are several ways to solve this problem:drop the thermal resistance from baseplate to ambient;reduce the output power;or lower the maximum ambient temperature.The thermal resistance can be reduced by blowing additional air over the converter; adding a heat sink;or both.The following equations can be used to calculate the maximum output power that can be delivered or the maximum thermal resistance the converter can tolerate.The maximum thermal resistance can then be used in conjunction with the Thermal Impedance Chart on page11to determine the correct combination of air flow and heat sink.Note:the combination in the chart should have a lower thermal resistance than the maximum calculated.In the this example,if nothing else is changed,the maximum output power would have to be reduced by using Equation4on page5as follows:Maximum Output Power={T baseplate(max)-T A}/[θBA{(1-η)/η}Maximum Output Power=(95-50)/[7.49x{(1-0.0.8838/0.8838)}]Note:95degrees C.was used instead of100degrees C.to add5degrees C.of margin. Maximum Output Power=45.6WattsIn this example,if the thermal Impedance can be changed,Equation5on page5can be used to calculate the required Maximum Thermal Impedance as follows:={T baseplate(max)-T A}/[P OUT{(1-η)/η}Maximum Thermal Impedance=θBAMaximum Thermal Impedance=θ=(95-50)/[53x{(1-0.0.8838/0.8838)}]BA=6.458Degrees C./WattMaximum Thermal Impedance=θBAAs can be seen by looking at the thermal impedance charts on the page8and page11,this example would require400Linear Feet per Minute(LFM)of airflow with no heat sink or a VSX60or VSX75with HSK-VSX heat sink and200Linear Feet per Minute(LFM)of airflow.Power Derating InformationThe following graphs show(as an alternative)the power derating of the VSX60and VSX75as a function of ambient temperature and air flow:Recommended AccessoriesF ollowing is a drawing of heat sink HSVSX from C&D Technologies which has beendesigned to be used with the VSX60 and VSX75 families of products.Air Flow LFMVSX Thermal Impedance*θΒΑ(DegC/Watt)With Heat sink HSVSXFree Air8.54200 5.14400 3.49600 2.82800 2.571000 2.23*Thermal impedance includes the thermal impedance of0.1degree C.per Watt of a thermally conductive interface material between VSX60and VSX75baseplate and heat sink.KIT*/PART #HEAT SINK INCLUDED IN KIT OVERALL PACKAGE HEIGHT** HSK-VSX HSVSX0.75"*The complete kits also include four mounting screws and a precut thermal interface material to provide improved thermal conductivity from the converter to the heat sink**The overall package height includes a 0.01" height for the interface pad.C&D Technologies tries to maintain a reasonable stock of the above heatsink kit.Please either contact the factory or one of our authorized distributors for price and availabilityFor answers to questions on information contained in this application note,please contact C&D Technologies,DC to DC Applications Group,by phone at(520)295-4104,by Fax at(520)295-4197,Email at swood@.or write us at the address shown below.HISTORY OF CHANGESRev A Fusing on page2changed from10A to6A.EMI filter changed on pages3-5Rev B EMI filter changed on pages3-5and thermal example added on pages8-11.Rev C Various corrections in grammarRev D Added on page8,the recommended method of mechanical tie down to FR4ground plane.Changed grounding recommendations on page2under“Safety”Updated Applications group Email Address on page12.Rev E Added VSX75Series throughout App Note.Changed Safety Agency Nomenclature on page2.Changed Normalized Efficiency Graph on page6.Changed both Power Derating Graphs on page10.New address and contact information on Page10.Rev F Added6new Derating Graphs for Unencapsulated VSX60and VSX75on Pages10-13.。