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MCOTS-C-28-12-HP Datasheet(PDF) 8 Page - SynQor Worldwide Headquarters |
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MCOTS-C-28-12-HP Datasheet(HTML) 8 Page - SynQor Worldwide Headquarters |
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8 / 13 page  Product # MCOTS-C-28-12-HP Phone 1-888-567-9596 www.synqor.com Doc.# 005-0005279 Rev. 1 06/16/09 Page 8 Output: Current: 12V 16A MCOTS-C-28-12-HP Technical Specification Figure A: Various circuits for driving the ON/OFF pin. Figure B: Internal ON/OFF pin circuitry BASICOPERATIONANDFEATURES This MIL-COTS converter series uses a two-stage power conversion topology. The first stage is a buck-converter that keepstheoutputvoltageconstantovervariationsinline,load, and temperature. The second stage uses a transformer to providethefunctionsofinput/outputisolationandvoltagestep- uporstep-downtoachievetheoutputvoltagerequired. Both the first stage and the second stage switch at a fixed frequency for predictable EMI performance. Rectification of the transformer’s output is accomplished with synchronous rectifiers. These devices, which are MOSFETs with a very low on-state resistance, dissipate far less energy than Schottky diodes.Thisistheprimaryreasonthattheconverterhassuch highefficiency,evenatverylowoutputvoltagesandveryhigh outputcurrents. Theseconvertersareofferedtotallyencasedtowithstandharsh environmentsandthermallydemandingapplications.Dissipation throughout the converter is so low that it does not require a heatsink for operation in many applications; however, adding a heatsink provides improved thermal derating performance in extremesituations. Thisseriesofconvertersusetheindustrystandardfootprintand pin-outconfiguration. CONTROLFEATURES REMOTE ON/OFF (Pin 2):TheON/OFFinput,Pin2,permits theusertocontrolwhentheconverterisonoroff.Thisinput is referenced to the return terminal of the input bus, Vin(-). TheON/OFFsignalisactivelow(meaningthatalowturnsthe converteron).FigureAdetailsfourpossiblecircuitsfordriving theON/OFFpin.FigureBisadetailedlookoftheinternalON/ OFFcircuitry. REMOTE SENSE(+) (Pins 7 and 5): The SENSE(+) inputs correctforvoltagedropsalongtheconductorsthatconnectthe converter’soutputpinstotheload. Pin 7 should be connected to Vout(+) and Pin 5 should be connectedtoVout(-)atthepointontheboardwhereregulation is desired. A remote connection at the load can adjust for a voltage drop only as large as that specified in this datasheet, thatis [Vout(+)-Vout(-)]–[Vsense(+)-Vsense(-)]< SenseRange%xVout Pins 7 and 5 must be connected for proper regulation of the output voltage.If these connections are not made, the converter will deliver an output voltage that is slightly higher thanitsspecifiedvalue. Note: the output over-voltage protection circuit senses the voltage across the output (pins 8 and 4) to determine when it should trigger, not the voltage across the converter’s sense leads(pins7and5).Therefore,theresistivedropontheboard should be small enough so that output OVP does not trigger, evenduringloadtransients. OpenCollectorEnableCircuit RemoteEnableCircuit DirectLogicDrive NegativeLogic (PermanentlyEnabled) ON/OFF Vin(_ ) ON/OFF ON/OFF Vin(_ ) ON/OFF 5V TTL/ CMOS Vin(_ ) Vin(_ ) TTL 5V 50k 50k ON/OFF Vin(_) 100pF OUTPUT VOLTAGE TRIM (Pin 6):TheTRIMinputpermitsthe usertoadjusttheoutputvoltageacrossthesenseleadsupor downaccordingtothetrimrangespecifications. To decrease the output voltage, the user should connect a resistorbetweenPin6andPin5(SENSE(-)input).Foradesired decreaseofthenominaloutputvoltage,thevalueoftheresistor shouldbe Rtrim-down= (511)-10.22(kW) ∆% where ∆% = Vnominal–Vdesiredx100% Vnominal To increase the output voltage, the user should connect a resistorbetweenPin6andPin7(SENSE(+)input).Foradesired increaseofthenominaloutputvoltage,thevalueoftheresistor shouldbe Trim graphs show the relationship between the trim resistor valueandRtrim-upandRtrim-down,showingthetotalrangethe outputvoltagecanbetrimmedupordown. Note:theTRIMfeaturedoesnotaffectthevoltageatwhichthe outputover-voltageprotectioncircuitistriggered.Trimmingthe outputvoltagetoohighmaycausetheover-voltageprotection circuittoengage,particularlyduringtransients. ItisnotnecessaryfortheusertoaddcapacitanceattheTrim pin.Thenodeisinternallybypassedtoeliminatenoise. Total DC Variation of VOUT:Fortheconvertertomeetitsfull specifications, the maximum variation of the dc value of VOUT, duetobothtrimmingandremoteloadvoltagedrops,shouldnot begreaterthanthatspecifiedfortheoutputvoltagetrimrange. PROTECTIONFEATURES Input Under-Voltage Lockout: The converter is designed toturnoffwhentheinputvoltageistoolow,helpingavoidan input system instability problem, described in more detail in the application note titled “Input System Instability” on our website.Thelockoutcircuitryisacomparatorwithdchysteresis. Whentheinputvoltageisrising,itmustexceedthetypicalTurn- On Voltage Threshold value (listed on the specifications page) before the converter will turn on. Once the converter is on, the input voltage must fall below the typical Turn-Off Voltage Thresholdvaluebeforetheconverterwillturnoff. Output Current Limit: The maximum current limit remains constant as the output voltage drops. However, once the impedanceoftheloadacrosstheoutputissmallenoughtomake theoutputvoltagedropbelowthespecifiedOutputDCCurrent- LimitShutdownVoltage,theconverterturnsoff. Theconverterthenentersa“hiccupmode”whereitrepeatedly turnsonandoffata5Hz(nominal)frequencywitha5%duty cycleuntiltheshortcircuitconditionisremoved.Thisprevents excessiveheatingoftheconverterortheloadboard. Output Over-Voltage Limit:Ifthevoltageacrosstheoutput pinsexceedstheOutputOver-VoltageProtectionthreshold,the converterwillimmediatelystopswitching.Thispreventsdamage totheloadcircuitdueto1)excessiveseriesresistanceinoutput current path from converter output pins to sense point, 2) a releaseofashort-circuitcondition,or3)areleaseofacurrent limit condition. Load capacitance determines exactly how high theoutputvoltagewillriseinresponsetotheseconditions.After 200mstheconverterwillautomaticallyrestart. Over-Temperature Shutdown: A temperature sensor on the converter senses the average temperature of the module. Thethermalshutdowncircuitisdesignedtoturntheconverter off when the temperature at the sensed location reaches the Over-Temperature Shutdown value. It will allow the converter toturnonagainwhenthetemperatureofthesensedlocation fallsbytheamountoftheOver-TemperatureShutdownRestart Hysteresisvalue. Rtrim-up (kW) where Vout=NominalOutputVoltage 511 _ 10.22 5.11VOUTx(100+∆%) 1.225 ∆% ∆% ) = ( _ |
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