NCP1397A/B, NCV1397A/B High Performance Resonant Mode .

NCP1397A/B, NCV1397A/BTYPICAL CHARACTERISTICS10.559.529.509.48VCC(min) (V)VCC(on) (V)10.5010.459.469.449.4210.409.4010.35 40 25 10 520 35 50 65 80TEMPERATURE ( C)959.38 40 25 10 5110 12595 110 125Figure 5. VCC(min) Threshold60.055106050950859.95FSW(max) (kHz)FSW(min) (kHz)Figure 4. VCC(on) Threshold20 35 50 65 80TEMPERATURE ( C)59.959.8559.850750650550459.75 40 200204060TEMPERATURE ( C)80100120503 40 25 10 5Figure 6. FSW(min) Frequency Clamp20 35 50 65 80TEMPERATURE ( C)95110 125Figure 7. FSW(max) Frequency Clamp0.66123.022.50.66022.00.659Vref(skip) (V)RFB (kW)21.521.020.520.00.6580.65719.50.65619.018.5 40 25 10 5203550658095110 1250.655 40 25 10 53550658095110 125TEMPERATURE ( C)TEMPERATURE ( C)Figure 8. Pulldown Resistor (RFB)Figure 9. Skip/Disable Threshold (Vref(skip))www.onsemi.com8Downloaded from Arrow.com.20

NCP1397A/B, NCV1397A/BTYPICAL CHARACTERISTICS17.09.016.08.515.08.07.5ROLA (W)ROHA (W)14.013.012.011.07.06.56.05.510.05.09.04.58.0 40 25 10 520 35 50 65 80TEMPERATURE ( C)954.0 40 25 10 5110 125114297113296112295111294110109108107110 12529329229129028910628810528710495Figure 11. Sink Resistance (ROL)Tdead(nom) (ns)Tdead(min) (ns)Figure 10. Source Resistance (ROH)20 35 50 65 80TEMPERATURE ( C) 40 25 10 520 35 50 65 80TEMPERATURE ( C)95286 40 25 10 5110 1254.0352.0604.0302.0554.025110 12595110 125Vlatch (V)Tdead(max) 5110 1254.005 40 25 10 52035506580TEMPERATURE ( C)TEMPERATURE ( C)Figure 14. Tdead(max)Figure 15. Latch Level (Vlatch)www.onsemi.com9Downloaded from Arrow.com.95Figure 13. Tdead(nom)Figure 12. Tdead(min)2.035 40 25 10 520 35 50 65 80TEMPERATURE ( C)

NCP1397A/B, NCV1397A/B1.03828.81.03628.61.03428.428.21.032IBO (mA)VBO (V)TYPICAL 427.21.022 40 25 10 520355065809527.0 40 25 10 5110 125203550658095110 125TEMPERATURE ( C)TEMPERATURE ( C)Figure 16. Brown Out Reference (VBO)Figure 17. Brown Out Hysteresis Current(IBO)1.0501781.0481761.046174Itimer1 (mA)Vref(fault) (V)1.0441.0421.0401721701.0381.0361681.0341.032 40 25 10 5203550658095166 40 25 10 5110 125203550658095TEMPERATURE ( C)TEMPERATURE ( C)Figure 18. Fault Input Reference (Vref(fault))Figure 19. Ctimer 1st Current (Itimer1)1.565110 1251.341.331.5601.32Itimer2 (mA)Vref(OCP) 261.530 40 25 10 5203550658095110 1251.25 40 25 10 53550658095TEMPERATURE ( C)TEMPERATURE ( C)Figure 20. OCP reference (Vref(OCP))Figure 21. Ctimer 2nd Current (Itimer2)www.onsemi.com10Downloaded from Arrow.com.20110 125

NCP1397A/B, NCV1397A/B4.0350.2884.0300.2860.2844.025VFB(off) (V)Vtimer(on) (V)TYPICAL 4.005 40 25 10 5203550658095110 1250.274 40 25 10 52050658095110 125TEMPERATURE ( C)Figure 22. Fault Timer Ending Voltage(Vtimer(on))Figure 23. FB Fault Detection Threshold(VFB(fault))1.0000.999Vtimer(off) (V)0.9980.9970.9960.9950.9940.9930.992 40 25 10 520 35 50 65 80TEMPERATURE ( C)95110 125Figure 24. Fault Timer Reset Voltage (Vtimer(off))www.onsemi.com11Downloaded from Arrow.com.35TEMPERATURE ( C)

NCP1397A/B, NCV1397A/BAPPLICATION INFORMATIONThe NCP1397A/B includes all necessary features to helpbuilding a rugged and safe switch mode power supplyfeaturing an extremely low standby power. The belowbullets detail the benefits brought by implementing theNCP1397A/B controller: Wide frequency range: A high speed Voltage ControlOscillator allows an output frequency excursion from50 kHz up to 500 kHz on Mlower and Mupper outputs. Adjustable dead time: Due to a single resistor wiredto ground, the user has the ability to include somedead time, helping to fight cross conduction betweenthe upper and the lower transistor. Adjustable soft start: Every time the controller startsto operate (power on), the switching frequency ispushed to the programmed starting value by externalcomponents (RFmin//RFstart) and slowly moves downtoward the minimum frequency, until the feedback loopcloses. The soft start discharge input (SS(dis))discharges the Soft Start capacitor before any IC restartexcluding the restart after Disable is released AND FBvoltage is higher than 0.3 V. The Soft Start dischargeswitch also activates in case the Fault input detects theoverload conditions. Adjustable minimum and maximum frequencyexcursion: In resonant applications, it is important tostay away from the resonating peak to keep operatingthe converter in the right region. Thanks to a singleexternal resistor, the designer can program its lowestfrequency point, obtained in lack of feedback voltage(during the startup sequence or in short circuitconditions). Internally trimmed capacitors offer a 3%precision on the selection of the minimum switchingfrequency. The adjustable upper stop being less preciseto 12%. Low startup current: When directly powered from thehigh voltage DC rail, the device only requires 300 mAto startup. Brown Out detection: To avoid operation from a lowinput voltage, it is interesting to prevent the controllerfrom switching if the high voltage rail is not within theright boundaries. Also, when teamed with a PFCfront end circuitry, the brown out detection can ensurea clean startup sequence with soft start, ensuring thatthe PFC is stabilized before energizing the resonanttank. The BO input features a 28 mA hysteresis currentfor the lowest consumption. Adjustable fault timer duration: When a fault isdetected on the Fault input or when the FB path isbroken, timer pin starts to charge an external capacitor.If the fault is removed, the timer opens the chargingpath and nothing happens. When the timer reaches itsselected duration (via a capacitor on Pin 3), all pulsesare stopped. The controller now waits for the dischargevia an external resistor on Pin 3 to issue a new cleanstartup sequence via soft start. Cumulative fault events: In the NCP1397A/B, thetimer capacitor is not reset when the fault disappears. Itactually integrates the information and cumulates theoccurrences. A resistor placed in parallel with thecapacitor will offer a simple way to adjust the dischargerate and thus the auto recovery retry rate. Overcurrent detection using Fault input: The faultinput is specifically designed to protect LLCapplication in case of short circuit or overload. In casethe voltage on this input grows above first threshold theItimer current source is activated and Fault timercapacitor starts charging. Simultaneously the Soft Startdischarge switch is activated to increase operatingfrequency of the converter. The IC stops operation incase the Fault timer elapses. The Fault input includesalso second fault comparator that: Speeds up the fault timer capacitor charging byincreasing the Itimer1 current to Itimer2 – NCP1397A Latches off the device – NCP1397BThe second fault comparator thus helps to protect the powerstage in case of hard short circuit (like shorted transformerwinding etc.) Skip cycle possibility: The absence of the soft start onthe Skip/Disable input (in case the VFB 0.3 V) offersan easy way to implement skip cycle when powersaving features are necessary. A simple resistive dividerfrom the feedback pin to the Skip/Disable input, andskip can be implemented. Broken feedback loop detection: Upon startup or anytime during operation, if the FB signal is missing, thetimer starts to charge timer capacitor. If the loop isreally broken, the FB level does not grow up before thetimer ends charging. The controller then stops all pulsesand waits until the timer pin voltage collapses to 1 Vtypically before a new attempt to restart, via thesoft start. If the optocoupler is permanently broken, ahiccup takes place. Common collector or common emitter optocouplerconnection options: This IC allows the designer toselect from two possible optocoupler configurations.Voltage Controlled OscillatorThe VCO section features a high speed circuitry allowingoperation from 100 kHz up to 1 MHz. However, as a divisionby two internally creates the two Q and /Q outputs, the finaleffective signal on output Mlower and Mupper switchesbetween 50 kHz and 500 kHz. The VCO is configured insuch a way that if the feedback pin voltage goes up, theswitching frequency also goes up. Figure 25 shows thearchitecture of the VCO oscillator.www.onsemi.com12Downloaded from Arrow.com.

NCP1397A/B, NCV1397A/BFBinternalVDDmaxFSW -maxImin0 to IFmaxVref -RtRt setsFmin for V(FB) 0SDCintQClkQR VDDIDTVrefIminABDTRDT setsthe deadtimeVCCVDDFmaxFmax setsthe maximum FSWFB RFB20 kVFB VFB(off)Start fault timerVb(off) Figure 25. The Simplified VCO ArchitectureVCCThe designer needs to program the maximum switchingfrequency and the minimum switching frequency. In LLCconfigurations, for circuits working above the resonantfrequency, a high precision is required on the minimumfrequency, hence the 3% specification. This minimumswitching frequency is actually reached when no feedbackcloses the loop. It can happen during the startup sequence,a strong output transient loading or in a short circuitcondition. By installing a resistor from Pin 4 to GND, theminimum frequency is set. Using the same philosophy,wiring a resistor from Pin 2 to GND will set the maximumfrequency excursion. To improve the circuit protectionfeatures, we have purposely created a dead zone, where thefeedback loop has no action. This is typically below 1.1 V.Figure 26 details the arrangement where the internal voltage(that drives the VCO) varies between 0 and 2.3 V. However,to create this swing, the feedback pin (to which theoptocoupler emitter connects), will need to swing typicallybetween 1.1 V and 5.3 V.FB R3100 kR28.7 kD12.3 VVref0.5 VFmaxRFmaxFigure 26. The OPAMP Arrangement Limits theVCO Modulation Signal between 0.5 and 2.3 Vwww.onsemi.com13Downloaded from Arrow.com. R111.3 k

NCP1397A/B, NCV1397A/BThis techniques allows us to detect a fault on the converterin case the FB pin cannot rise above 0.3 V (to actually closethe loop) in less than a duration imposed by theprogrammable timer. Please refer to the fault section fordetailed operation of this mode.As shown on Figure 26, the internal dynamics of the VCOcontrol voltage will be constrained between 0.5 V and 2.3 V,whereas the feedback loop will drive Pin 6 (FB) between1.1 V and 5.3 V. If we take the default FB pin excursionnumbers, 1.1 V 50 kHz, 5.3 V 500 kHz, then the VCOmaximum slope will be:500 k * 50 k4.2 107 kHz/VFigures 27 and 28 portray the frequency evolutiondepending on the feedback pin voltage level in a differentfrequency clamp combination.Figure 28. Here a Different Minimum Frequency wasProgrammed as well as a Maximum FrequencyExcursionPlease note that the previous small signal VCO slope hasnow been reduced to 300k / 4.1 71 kHz / V on Mupper andMlower outputs. This offers a mean to magnify the feedbackexcursion on systems where the load range does not generatea wide switching frequency excursion. Due to this option,we will see how it becomes possible to observe the feedbacklevel and implement skip cycle at light loads. It is importantto note that the frequency evolution does not have a reallinear relationship with the feedback voltage. This is due tothe deadtime presence which stays constant as the switchingperiod changes.The selection of the three setting resistors (Fmax, Fmin anddeadtime) requires the usage of the selection chartsdisplayed below:Figure 27. Maximal Default Excursion,Rt 41 kW on Pin 4 and RF(max) 1.9 kW on Pin 2www.onsemi.com14Downloaded from Arrow.com.

NCP1397A/B, NCV1397A/B1900VCC 15 VVFB 6.5 VDT 300 ns550170015001300DT (ns)Fmax (kHz)450350Fmin 200 kHz2501100900700500150Fmin 50 kHz501.911.921.931.93001003.541.913.5RFmax (kW)Figure 29. Maximum Switching Frequency ResistorSelection Depending on the Adopted MinimumSwitching Frequency23.533.5 43.5 53.5RDT (kW)63.573.5 83.5Figure 32. Deadtime Resistor SelectionORing capability and optocoupler connectionconfigurations500If for any particular reason, there is a need for a frequencyvariation linked to an event appearance (instead of abruptlystopping pulses), then the FB pin lends itself very well to theaddition of other sweeping loops. Several diodes can easilybe used perform the job in case of reaction to a fault eventor to regulate on the output current (CC operation).Figure 33 shows how to do it.VCC 15 VVFB 1 VDT 300 ns450Fmin (kHz)400350300250VCC20015010024681012RFmin (kW)14161820In1In2Figure 30. Minimum Switching Frequency ResistorSelection (Fmin 100 kHz to 500 kHz)100Fmin (kHz)8060504030203040506070RFmin (kW)8090100 110Figure 31. Minimum Switching Frequency ResistorSelection (Fmin 20 kHz to 100 kHz)www.onsemi.com15Downloaded from Arrow.com.20 kThe VCO configuration used in this IC also offers an easyway to connect optocoupler (or pulldown bipolar) directlyto the Rt pin instead of FB pin (refer to Figures 34 and 35).The optocoupler is then configured as “common emitter”and the operating frequency is controlled by the current thatis taken out from the Rt pin – we have current controlleroscillator (CCO). If one uses this configuration it is neededto maintain FB pin voltage between 0.3 V and 1 V otherwisethe FB fault will be detected. The FB pin can be still used foropen FB loop detection in some applications – to do so it isneeded to keep optcoupler emitter voltage higher then 0.3 Vfor nominal load conditions. One needs to take RFBpulldown resistor into account when using thisconfiguration. It is possible to implement skip mode usingSkip/disable input and emitter resistors Rskip1 and Rskip2.7020VCOFigure 33. Thanks to the FB Configuration, LoopORing is Easy to ImplementVCC 15 VVFB 1 VDT 300 ns90FB

NCP1397A/B, NCV1397A/BFstart(adj) RFstart/RFminFmin(adj) RFminFmax(adj) Rc Rskip1 P1397CSSOK1Rskip1Rskip2Figure 34. Feedback Configuration Using Direct Connection to the Rt PinRbiasFstart(adj) RFstart/RFminFmin(adj) RFminFmax(adj) Rc Rskip1 P1397CSSOK1Rskip1Rskip21N4148Figure 35. Feedback Configuration Using Direct Connection to the Rt Pin – No Open FB Loop DetectionDead Time ControlDeadtime control is an absolute necessity when thehalf bridge configuration comes to play. The deadtimetechnique consists in inserting a period during which bothhigh and low side switches are off. Of course, the deadtimeamount differs depending on the switching frequency, hencethe ability to adjust it on this controller. The option rangesbetween 100 ns and 2 ms. The deadtime is actually made bycontrolling the oscillator discharge current. Figure 36portrays a simplified VCO circuit based on Figure 25.During the discharge time, the clock comparator is high andinvalidates the AND gates: both outputs are low. When thecomparator goes back to the low level, during the timingcapacitor Ct recharge time, A and B outputs are validated.By connecting a resistor RDT to ground, it creates a currentwhose image serves to discharge the Ct capacitor: we controlthe dead time. The typical range evolves between 100 ns(RDT 3.5 kW) and 2 ms (RDT 83.5 kW). Figure 39 showsthe typical waveforms.www.onsemi.com16Downloaded from Arrow.com.

NCP1397A/B, NCV1397A/BVDDIcharge:FSW(min) FSW(max)SD QClk IdisQRCt 3 V 1 VVrefDTRDTABFigure 36. Dead time GenerationSoft Start SequenceIn resonant controllers, a soft start is needed to avoidsuddenly applying the full current into the resonating circuit.With this controller the soft start duration is fully adjustableusing eternal components. The purpose of the Soft Start pinis to discharge Soft Start capacitor before IC restart and incase of fault conditions detected by Fault input.Once the controller starts operation, the Soft Startcapacitor (refer to Figure 37) is fully discharged and thus itstarts charging from the Rt pin. The charging currentincreases operating frequency of the controller above Fmin.As the soft start capacitor charges, the frequency smoothlydecreases down to Fmin. Of course, practically, the feedbackloop is supposed to take over the VCO lead as soon as theoutput voltage has reached the target. If not, then theminimum switching frequency is reached and a fault isdetected on the feedback pin (typically below 300 mV).Figure 38 depicts a typical LLC startup using NCP1397A/Bcontroller.SSActionTarget isReachedFigure 38. A Typical Startup Sequence on a LLCConverter Using NCP1397Please note that the soft start capacitor is discharged in thefollowing conditions: A startup sequence During auto recovery burst mode A brown out recovery A temperature shutdown recoveryThe skip/disable input undergoes a special treatment.Since we want to implement skip cycle using this input, wecannot activate the soft start every time the feedback pinstops the operations in low power mode. Therefore, whenthe skip/enable pin is released, no soft start occurs to offerthe best skip cycle behavior. However, it is very possible tocombine skip cycle and true disable, e.g. via ORing diodesdriving Pin 8. In that case, if a signal maintains theskip/disable input high long enough to bring the feedbacklevel down (below 0.3 V) since the output voltage starts tofall down, then the soft start discharge switch is Fstart(adj) RFstart/RFminFmin(adj) RFminFmax(adj) RFmaxFigure 37. Soft Start Components Arrangementwww.onsemi.com17Downloaded from Arrow.com.

NCP1397A/B, NCV1397A/BPlot1Vct in Volts4.003.002.001.00Ct Voltage0Plot2Clock in Volts16.0Clock PulsesDT12.08.004.000DTPlot3Difference in Volts8.00DT4.000 4.00A B 8.0056.2 m65.9 m75.7 mtime in seconds85.4 m95.1 mFigure 39. Typical Oscillator WaveformsBrown Out protectionVbulkThe Brown Out circuitry (BO) offers a way to protect theresonant converter from low DC input voltages. Below agiven level, the controller blocks the output pulses, above it,it authorizes them. The internal circuitry, depicted byFigure 40, offers a way to observe the high voltage (HV)rail. A resistive divider made of Rupper and Rlower, brings aportion of the HV rail on Pin 5.

BO Reset FF Vref Skip/Disable Skip/ Disabl e V CC Timeout Fault Fault Mlowe r GND IBO 20 ns Noise Filter Fault Vref(fault) NC V BOOT Muppe r HB UVLO Fast Fault Vref(OCP) Vdd Itimer2 Level Shifter 20 ms Noise Filter Fault PON Reset Enable (if Vfb 0.3V) 20 ms Noise Filter 1 ms Noise Filter Downloaded from Arrow.com.