LTC4368 – 100V UV/OV And Reverse Protection Controller .

LTC4368Pin FunctionsExposed Pad: The exposed pad may be left open or connected to device ground.FAULT: Fault Indication Output. Connect to a pull-up resistor. This high voltage open drain output is pulled low if thereis a voltage or current fault, if SHDN is low, or if VIN hasnot risen above VIN(UVLO). Leave unconnected if unused.GATE: Gate Drive Output for External N-channel MOSFETs.An internal charge pump provides 35µA of pull-up currentand up to 13.1V of enhancement to the gate of an externalMOSFET. When turned off, GATE is pulled just below thelower of VIN or VOUT. When VIN goes negative, GATE isautomatically connected to VIN.GND: Device Ground.OV: Overvoltage Comparator Input. Connect this pin to anexternal resistive divider to set the desired VIN overvoltage fault threshold. This input connects an accurate, fast(1µs) comparator with a 0.5V rising threshold and 25mVof hysteresis. When OV rises above its threshold, a 60mAcurrent sink pulls down on the GATE output. When OVfalls back below 0.475V, and after a 32ms GATE turn-ondelay waiting period, the GATE charge pump is enabled.The low leakage current on this input allows the use oflarge valued resistors for the external resistive divider.Connect to GND if unused.disconnecting the load from the input. After a reversecurrent fault, when VOUT falls 100mV below VIN, theLTC4368 automatically turns on the external MOSFETs.A forward overcurrent fault uses the RETRY pin to set theconditions for reconnecting power to the load. Connectto VOUT if unused.SHDN: Shutdown Control Input. Assuming no voltage orcurrent faults, SHDN high enables the GATE charge pumpwhich in turn enhances the gate of the external N-channelMOSFETs. A low on SHDN generates a pull down on theGATE output with a 90µA current sink and places theLTC4368 in low current mode (5µA). If a forward overcurrent condition latches off the external MOSFETs (RETRYgrounded), the SHDN pin must be toggled low then highto re-enable the charge pump that enhances the externalMOSFETs. If VIN goes above 80V, the SHDN pin voltagemust be kept below 80V.UV: Undervoltage Comparator Input. Connect this pin to anexternal resistive divider to set the desired VIN undervoltagefault threshold. This input connects to an accurate, fast(1µs) comparator with a 0.5V falling threshold and 25mVof hysteresis. When UV falls below its threshold, a 60mAcurrent sink pulls down on the GATE output. When UVrises back above 0.525V, and after a 32ms GATE turn-ondelay waiting period, the GATE charge pump is enabled.The low leakage current on this input allows the use oflarge valued resistors for the external resistive divider. Ifunused and VIN is less than 80V, connect to VIN with a510k resistor.RETRY: Retry or Latch-Off Selection Input. Connect toground to latch off the MOSFETs after a forward overcurrentfault. To turn the external MOSFETs back on, the SHDNpin must be toggled low then high. Connect RETRY to anexternal capacitor to configure a 5.5ms/nF delay beforethe MOSFETs automatically turn on again. Leave unconnected if unused.VIN: Power Supply Input. Maximum protection range: –40Vto 100V. Operating range: 2.5V to 60V. This pin can behot swapped and has a 2.2V UVLO.SENSE: Overcurrent Sense Input. Connect a currentsense resistor between SENSE and VOUT. This inputdetects overcurrent faults in both directions: forwardat VSENSE 50mV, and reverse at VSENSE –50mV(LTC4368-1 option) or VSENSE –3mV (LTC4368-2option). When an overcurrent fault is detected, a 60mAcurrent sink pulls down on the GATE output, thus quicklyVOUT: Output Voltage Sense Input. Connect a current senseresistor between VOUT and SENSE. The GATE charge pumpvoltage is referenced to VOUT. It is used as the charge pumpinput when VOUT is greater than approximately 5V. Thereverse current fault comparators require that VOUT riseabove its 2.2V UVLO. VOUT cannot be hot swapped withsupplies above 24V. Place at least 1µF from VOUT to GND.84368fFor more information www.linear.com/LTC4368

LTC4368Block DiagramVIN–40V TO 100VGATESENSE50mV–5VVOUTENABLE50mV (4368-1)3mV (4368-2)CLOSES SWITCHWHEN VIN IS NEGATIVEGATECHARGEPUMPf 400kHz– REV RESET –LDO –OC REV– REVERSEPROTECTION VOUTVOUT– –OC FWDOVERCURRENTCOMPARATORSVIN100mVIGATE35µA17µA31 CYCLESSLOWOFFFASTOFFFWD RESETSTART TIMERRETRY3.5µA90µA60mAGATE PULLDOWNLOGICFORWARD OVERCURRENTTIMERSHDNVIN2.2VUVLOUV0.5VOV0.5VDELAY TIMERSLOGIC–FAULT 25mVHYSTERESIS–GND4368 BD4368fFor more information www.linear.com/LTC43689

LTC4368OperationMany of today’s electronic systems get their power fromexternal sources such as wall adapters, batteries andcustom power supplies. Figure 1 shows a supply arrangement using a DC barrel connector. Power is supplied byan AC adapter or, if the plug is withdrawn, by a removablebattery. Note that the polarity of the AC adapter and barrelconnector varies by manufacturer. Trouble arises whenany of the following occurs:of a single catastrophic event, or over time as devicesdegrade from repeated overstress.The LTC4368 limits these errant overvoltage and overcurrent conditions and helps extend the life of the electronicsystems it protects. When the part detects an overcurrentor overvoltage fault, it isolates the input supply from theload by turning off the external back-to-back MOSFETs.The LTC4368 provides accurate overvoltage and undervoltage comparators to ensure that power is applied tothe load only if the input supply meets the user selectablevoltage window. Additionally, two accurate overcurrentcomparators disconnect the load from the supply whenexcessive current flows in either the forward ( 50mV/RSENSE) or reverse (–50mV or –3mV/RSENSE) direction.Reverse supply voltage protection circuits automaticallyisolate the load from negative input voltages. During normaloperation, a high voltage charge pump enhances the gateof dual external N-channel power MOSFETs, thus providinga low loss path for qualified power. Power consumptionis 5µA during shutdown and 80µA while operating. TheLTC4368 integrates all these functions in small 10-lead3mm 3mm DFN and MSOP packages. The battery is installed backwards A wall adapter of opposite polarity is attached A wall adapter of excessive voltage is attached A wall adapter with an AC output is attached The battery is discharged below a safe level The load or the input is shorted to ground or to anothersupply Excessive current flows from the supply to the load orfrom the load to the supplyThese conditions, if unchecked, can damage electronicsystems and their connectors. Damage can take the formBI-DIRECTIONALOVERCURRENT PROTECTION–40V TO 100V PROTECTION RANGE ACADAPTERINPUTBATTERY2.5V TO 60VOPERATING RANGEM1 INSENSEGATEVOUTR4SHDNOV, UV PROTECTIONTHRESHOLDS SET TOSATISFY LOAD CIRCUITR3LTC4368-2UVFAULTOVRETRYR2R1GNDCRETRY4368 F01Figure 1. Polarity Protection for DC Barrel Connectors104368fFor more information www.linear.com/LTC4368

LTC4368Applications InformationVIN24VM1M2PSMN4R8-100BSE SiR662INRUSHCONTROL 50mV0.004ΩVOUT7V TO 36V–0.75A TO 12.5A–3mV22k2.2nFR4464kOV 36VUV RY1200ms COOLDOWNAFTER FORWARDOC FAULTR2121kR129.4k0.22µFGND4368 F02Figure 2. LTC4368-2 Protects Load from Voltage (–40V to 100V) and Current (–0.75A to 12.5A) FaultsVoltages at VIN outside of the 7V to 36V range are preventedfrom getting to the load and can be as high as 100V andas negative as –40V. Load currents (including inrushcurrents) above 12.5A (forward from VIN to VOUT) andbelow –0.75A (reverse from VOUT to VIN) will cause theload to be disconnected from VIN. The circuit of Figure 2protects against negative voltages at VIN as shown. Notethat the SOA and voltage requirements are not the samefor the two external MOSFETs. During power-up, the inputMOSFET (M1) will stand off more voltage (up to VIN) thanthe output MOSFET (M2). The body diode of M2 will limitits drain to source voltage. This allows the use of smallerMOSFETs at the output.During normal operation, the LTC4368 provides up to13.1V of gate enhancement to the external back-to-backN-channel MOSFETs. This turns on the MOSFETs, thusconnecting the load at VOUT to the supply at VIN.GATE DriveThe LTC4368 turns on the external N-channel MOSFETs bydriving the GATE pin above VOUT. The voltage differencebetween the GATE and VOUT pins (gate drive) is a functionof VIN and VOUT.Figure 3 highlights the dependence of the gate drive on VINand VOUT. When system power is first turned on (SHDN lowto high, SENSE VOUT 0V), gate drive is at a maximumfor all values of VIN. This helps prevent startup problemsinto heavy loads by ensuring that there is enough gatedrive to support the load.14TA 25 CIGATE –1µA12VIN 12V, 60V10 VGATE (V)The LTC4368 is an N-channel MOSFET controller thatprotects a load from overvoltage faults (both positive andnegative) and from overcurrent faults (both forward andreverse). A typical application circuit using the LTC4368-2is shown in Figure 2. The circuit provides a low loss connection from VIN to VOUT as long as there are no voltageor current faults.8VIN 5V6VIN 3.3V4VIN 2.5V200510VOUT (V)154365 F03Figure 3. Gate Drive (GATE – VOUT) vs VOUT4368fFor more information www.linear.com/LTC436811

LTC4368Applications InformationAs VOUT ramps up from 0V, the absolute value of the GATEvoltage remains fixed until VOUT is greater than the lowerof (VIN – 1V) or 5V. Once VOUT crosses this threshold, gatedrive begins to increase up to a maximum of 13.1V. Thecurves of Figure 3 were taken with a GATE load of –1µA.If there were no DC load on GATE, the gate drive for eachVIN would be slightly higher.Note that when VIN is at the lower end of the operatingrange, the external N-channel MOSFET must be selectedwith a correspondingly lower threshold voltage.Overvoltage and Undervoltage ProtectionThe LTC4368 provides two accurate comparators to monitor for overvoltage (OV) and undervoltage (UV) conditionsat VIN. If the input supply rises above the user adjustableOV threshold, the gates of the external MOSFETs arequickly turned off, thus disconnecting the load from theinput. Similarly, if the input supply falls below the useradjustable UV threshold, the gates of the external MOSFETsare quickly turned off. Figure 4 shows a UV/OV applicationfor an input supply of 12V.12VUVUVTH 3.5VR2243k0.5VOVOVTH 18VR159k25mVOVCOMPARATORDISCHARGE GATEWITH 60mA SINK 25mV0.5VVUVVUV VUVHYSTtFAULTFAULTtD(FAST)tD(ON)EXTERNAL N-CHANNEL MOSFETSTURN OFFFigure 5. UV Timing (OV (VOV – VOVHYST), SHDN 1.2V)– UV4368 F05UVCOMPARATORR31820kFigure 5 shows the timing associated with the UV pin.Once a UV fault propagates through the UV comparator(tFAULT), the FAULT output is asserted low and a 60mAcurrent sink discharges the GATE pin. As VOUT falls, theGATE pin tracks VOUT.GATELTC4368VINThe external resistive divider allows the user to selectan input supply range that is compatible with the load atVOUT. Furthermore, the UV and OV inputs have very lowleakage currents (typically 1nA at 100 C), allowing forlarge values in the external resistive divider. In the application of Figure 4, the load is connected to the supply only ifVIN lies between 3.5V and 18V. In the event that VIN goesabove 18V or below 3.5V, the gate of the external N-channelMOSFET is immediately discharged with a 60mA currentsink, thus isolating the load from the supply.–Figure 6 shows the timing associated with the OV pin.Once an OV fault propagates through the OV comparator(tFAULT), the FAULT output is asserted low and a 60mAcurrent sink discharges the GATE pin. As VOUT falls, theGATE pin tracks VOUT.OVVOVVOV – VOVHYST4368 F04tFAULTFigure 4. UV, OV Comparators Monitor 12V SupplyFAULTtD(FAST)GATEtD(ON)EXTERNAL N-CHANNEL MOSFETTURNS OFF4368 F06Figure 6. OV Timing (UV (VUV VUVHYST), SHDN 1.2V)124368fFor more information www.linear.com/LTC4368

LTC4368Applications InformationWhen both the UV and OV faults are removed, the external MOSFETs are not immediately turned on. The inputsupply must remain within the user selected power goodwindow for typically 32ms (tD(ON)) before the load is againconnected to the supply. This recovery timeout periodfilters noise (including line noise) at the input supply andprevents chattering of power at the load.The example of Figure 4 uses standard 1% resistor values.The following parameters were selected:Procedure for Selecting UV/OV External Resistor ValuesThe resistor values can then be solved:The following 3-step procedure helps select the resistorvalues for the resistive divider of Figure 4. This procedureminimizes UV and OV offset errors caused by leakagecurrents at the respective pins.1. Choose maximum tolerable offset at the UV pin, VOS(UV).Divide by the worst case leakage current at the UV pin,IUV (10nA). Set the sum of R1 R2 equal to VOS(UV)divided by 10nA. Note that due to the presence of R3,the actual offset at UV will be slightly lower.R1 R2 VOS(UV)I UVVOS(UV)I UVVOS(UV)I UVOVTH 18V1. R1 R2 2. R3 2 3mV 300k10nA3mV (3.5V – 0.5V) 1.8M10nAThe closest 1% value: R3 1.82M3. R1 300k 1.82M 58.9k2 18VThe closest 1% value: R2 243KTherefore: OV 17.93V, UV 3.51V.Limiting Inrush Current During Turn On3. Select the desired VIN OV trip threshold, OVTH. Find thevalues of R1 and R2:R2 UVTH 3.5VR2 300K – 59K 241K UV TH – 0.5V 0.5V VOS(UV) R3 I UV R1 0.5VOV THIUV 10nAThe closest 1% value: R1 59K2. Select the desired VIN UV trip threshold, UVTH. Find thevalue of R3:R3 VOS(UV) 3mVCharging large capacitors on VOUT can lead to excessiveinrush currents when LTC4368 turns on the externalN-channel MOSFET. The maximum slew rate at the GATEpin can be reduced by adding a capacitor on the GATE pin:Slew Rate IGATE(UP)CGATE– R14368fFor more information www.linear.com/LTC436813

LTC4368Applications InformationSince the MOSFET acts like a source follower, the slewrate at VOUT equals the slew rate at GATE. Therefore, theinrush current due to the capacitance on VOUT is given by:IINRUSH COUT IGATE(UP)CGATEFor example, a 1A inrush current into a 100µF outputcapacitance requires a GATE capacitance of (usingIGATE(UP) 35µA):CGATE35µA COUT IINRUSHCGATE 35µA 100µF 3.5nF1AThe 3.3nF CGATE capacitor in the application circuit ofFigure 7 limits the inrush current to just over 1A. RGATEprevents CGATE from slowing down the reverse polarityprotection circuits. It also stabilizes the fast pull-downcircuits and prevents chatter during fault conditions. SetRGATE to 22k for most applications.2.5AFDS3992100V DUALM1M2VIN24VRSENSE0.02ΩRGATE22kINRUSHCONTROL: 1AIOUT 2.5A –0.15ACOUT100µFCGATE3.3nFVOUTSENSE50mV –TURN OFFMOSFETSGATEU2TURN MOSFETSBACK ONU3– VINIOUT– U1–VOUTVINLTC4368-2 –100mVTURN MOSFETSBACK ON AFTER31 CYCLESSHDNSTARTTIMER31 CYCLESRETRYRESET FORWARDOC LATCHOC FORWARD TIMER/LATCHCRETRY0.22µF4368 F07Figure 7. Overcurrent Comparators Monitor 2.5A/–0.15ACurrent Faults14Forward overcurrent protection prevents large currentsfrom flowing from VIN to VOUT. This threshold current isdetermined by the external sense resistor (RSENSE) and aninternal comparator (Figure 7, U1) with a 50mV threshold:IOC,FWD 50mVRSENSEFor the example of Figure 7, if 2.5A flows to the outputacross the 20mΩ sense resistor, the external MOSFETs(M1, M2) are immediately (8µs) turned off. This disconnects the load from the input supply.Note that during initial startup, the output capacitance(COUT) charges from ground to VIN. To prevent this capacitive inrush current (IINRUSH) from falsely triggeringthe forward overcurrent comparator, place an inrushlimiting capacitor (CGATE) on the GATE pin (see LimitingInrush Current During Turn-On). This inrush current plusthe output current must be less than the desired forwardovercurrent threshold:IOC,FWD IINRUSH IOUTFor the example of Figure 7, the 3.3nF GATE capacitorand the 100µF output capacitor limit the inrush current(IINRUSH) to approximately 1A. This means that the outputcurrent (IOUT) must be less than 1.5A during turn on inorder to avoid a forward overcurrent fault during turn on.Once VOUT has ramped to its final value, the output currentis limited to 2.5A.Once a forward overcurrent fault is triggered, there aretwo application choices for turning the external MOSFETsback on:3mV– Forward Overcurrent Fault1. Automatically restart by placing an external capacitor onthe RETRY pin. An internal cool-down timer will charge/discharge this capacitor 31 times with a 5.5ms/nF totaldelay. At the end of this delay, the external MOSFETsare turned back on, thus reconnecting the load to theinput supply. The 0.22µF capacitor (CRETRY) in theapplication of Figure 7 yields a 1200ms cool-downtimer delay. Note that the adjustable cool-down periodprovides the user with a means of keeping the external4368fFor more information www.linear.com/LTC4368

LTC4368Applications InformationMOSFETs within the rated SOA (safe operating area).See Figure 8 timing diagram.2. Latch off the MOSFETs by grounding the RETRY pin(no external RETRY capacitor needed). This latchesthe forward overcurrent fault. The external MOSFETsare kept in the off condition until the SHDN input pin istoggled low then high (tCLEAR pulse width tLOWPWR).See Figure 9 timing diagram.50mVSENSE – VOUT0mVSTEADY STATE LOADEXTERNAL N-CHANNELMOSFETs TURN OFFGATE31 CYCLES(1200ms COOL-DOWN PERIOD)RETRYFAULT4368 F08Figure 8. Forward Overcurrent Fault with 0.22µF RETRY Capacitor50mVSENSE – VOUT0mVSTEADY STATE LOADIINRUSHLIMITEDSTEADY STATE LOADt p(GATE)EXTERNAL N-CHANNELMOSFETs TURN OFFGATEEXTERNAL N-CHANNELMOSFETs TURN BACK ONSHDN–3mV –3mV –0.15ARSENSE 20mΩtIf –0.15A flows from the output across the 20mΩ senseresistor, the external MOSFETs (M1,M2) are immediately(8µs) turned off.VOUT VIN – 100mV4368 F08Figure 9. Forward Overcurrent Fault with RETRY Pin GroundedFAUL

100V UV/OV and Reverse Protection Controller with Bidirectional Circuit Breaker 24V Application with 10A Circuit Breaker applicaTions n Wide Operating Voltage Range: 2.5V to 60V n Overvoltage Protection to 100V n Reverse Supply Protection to –40V n Bidirectional Electronic Circuit Breaker: n 50mV For