LTC3721-1 - Push-Pull PWM Controller

1 LTC3721-11sn37211 37211fsAPPLICATIO SUFEATURESTYPICAL APPLICATIOUDESCRIPTIOUThe LTC 3721-1 Push-Pull PWM Controller provides all ofthe control and protection functions necessary for com-pact and highly efficient, isolated power converters. Highintegration minimizes external component count, whilepreserving design robust Push-Pull output stages switch at half theoscillator frequency. Dead-time is independently pro-grammed with an external resistor. A UVLO program inputprovides precise system turn-on and turn off voltages. TheLTC3721-1 features peak current mode control with pro-grammable slope compensation and leading LTC3721-1 features extremely low operating andstart-up currents and reliable short-circuit andovertemperature protection.

2 The LTC3721-1 is offered in16-pin SSOP and (4mm 4mm) QFN packages. Telecommunications, Infrastructure Power Systems Distributed Power Architectures Server Power Supplies High Density Power Modules, LTC and LT are registered trademarks of Linear Technology Corporation. High Efficiency Push-Pull PWM Sink, 1A Source Output Drivers Adjustable Push-Pull Dead-Time Adjustable System Undervoltage Lockout andHysteresis Adjustable Leading Edge Blanking Low Start-Up and Quiescent Currents Current Mode Operation Single Resistor Slope Compensation VCC UVLO and 25mA Shunt Regulator Programmable Fixed Frequency Operation to 1 MHz Soft-Start, Cycle-by-Cycle Current Limiting andHiccup Mode Short-Circuit Protection 5V, 15mA Low Dropout Regulator 16-Pin SSOP and (4mm 4mm)

3 QFN PackagesPush- pull PWM ControllerRCSVOUTVOUTV+VOUTRTOPGND-FLT14 31 GND-SCOLLRREFCOMPRMID37211 TA01 VINFROMAUXILIARYWINDINGVREF+DRVADRVBCSVC CDPRGLTC3721-1 VREFCOMPUVLOCTRLEBSSFB GNDI solated Push-Pull ConverterLTC3721-12sn37211 37211fsVCC to GND (Low Impedance Source) .. to 10V(Chip Self-Regulates at )UVLO to GND .. to VCCAll Other Pins to GND(Low Impedance Source) .. to (Current Fed) .. 40mAORDER PARTNUMBERGN PARTMARKINGTJMAX = 125 C, JA = 100 C/WConsult LTC Marketing for parts specified with wider operating temperature AXI U RATI GSWWWUPACKAGE/ORDER I FOR ATIOUUW(Note 1)ELECTRICAL CHARACTERISTICSThe denotes the specifications which apply over the full operatingtemperature range, otherwise specifications are at TA = 25 C.

4 VCC = unless otherwise Output Current .. Self-RegulatedOperating Temperature (Notes 5,6) LTC3721-1 .. 40 C to 85 CStorage Temperature Range .. 65 C to 125 CLead Temperature (GN Package only)(Soldering, 10sec) .. 300 CORDER PARTNUMBERUF PARTMARKING37211 LTC3721 EUF-1 TJMAX = 125 C, JA = 100 C/WEXPOSED PAD IS GND(PIN17) MUST BE SOLDERED TO PCB12345678 TOP VIEWGN PACKAGE16-LEAD PLASTIC SSOP161514131211109 VREFNCNCDRVBVCCDRVAGNDCTNCUVLOSSFBRLEBCO MPCSDPRGSYMBOLPARAMETERCONDITIONSMINTYPM AXUNITSI nput SupplyVCCUVVCC Undervoltage LockoutMeasured on UVLO HysteresisMeasured on CurrentVCC = VUVLO 145230 AICCRNO perating CurrentNo load on Outputs36mAVSHUNTS hunt Regulator VoltageCurrent into VCC = ResistanceCurrent into VCC = 10mA to SUVLOS ystem UVLO ThresholdMeasured on UVLO Pin, 10mA into UVLO Hysteresis CurrentCurrent Flows Out of UVLO Pin.

5 10mA into A16171514135678 TOP VIEWUF PACKAGE16-LEAD (4mm 4mm) PLASTIC QFN91011124321 DRVBVCCDRVAPGNDFBRLEBCOMPCSNCVREFUVLOSSS GNDCTNCDPRGLTC3721-13sn37211 37211fsELECTRICAL CHARACTERISTICSThe denotes the specifications which apply over the full operatingtemperature range, otherwise specifications are at TA = 25 C. VCC = unless otherwise Width ModulatorROSRamp Offset VoltageMeasured on COMP, CS = Discharge CurrentCS = 1V, COMP = 0V, CT = 4V50mAISLPS lope Compensation CurrentMeasured on CS, CT = 1V30 ACT = ADCMAXM aximum Duty CycleCOMP = Duty CycleCOMP = 0V 0%DTADJDead-Time130nsOscillatorOSCII nitial AccuracyTA = 25 C, CT = 270pF220250280kHzOSCTVCC VariationVCC = to 33%OSCVCT Ramp AmplitudeMeasured on AmplifierVFBFB Input VoltageCOMP = , (Note 3) Input RangeMeasured on FB, (Note 4) GainCOMP = 1V to 3V, (Note 3)7090dBIIBI nput Bias CurrentCOMP = , (Note 3)

6 550nAVOHO utput HighLoad on COMP = 100 LowLoad on COMP = 100 Source CurrentCOMP = AISINKO utput Sink CurrentCOMP = AccuracyTA = 25 C, Measured on RegulationLoad on VREF = 100 A to 5mA215mVREFLNLine RegulationVCC = to VariationLine, load and Temperature CurrentVREF Shorted to GND183045mAPush- pull OutputsDRVH(x)Output High VoltageIOUT(x) = (x)Output Low VoltageIOUT(x) = (x) pull -Up ResistanceIOUT(x) = 10mA to RDL(x) pull -Down ResistanceIOUT(x) = 10mA to TDR(x)Rise-TimeCOUT(x) = 1nF10nsTDF(x)Fall-TimeCOUT(x) = 1nF10nsCurrent Limit and ShutdownCLPPP ulse by Pulse Current Limit ThresholdMeasured on CS280300320mVCLSDS hutdown Current Limit ThresholdMeasured on CS475600725mVCLDELC urrent Limit Delay to Output100mV Overdrive on CS, (Note 2)80nsSSISoft-Start CurrentSS = ALTC3721-14sn37211 37211fsSSRSoft-Start Reset ThresholdMeasured on Reset ThresholdMeasured on CHARACTERISTICSThe denotes the specifications which apply over the full operatingtemperature range, otherwise specifications are at TA = 25 C.

7 VCC = unless otherwise 1: Absolute Maximum Ratings are those values beyond which the lifeof a device may be 2: Includes leading edge blanking delay, RLEB = 20k, not tested 3: FB is driven by a servo loop amplifier to control VCOMP for 4: Set FB to , and insure that COMP does not phase 5: The LTC3721 1 is guaranteed to meet performance specificationsfrom 0 C to 85 C. Specifications over the 40 C to 85 C operatingtemperature range are assured by design, characterization and correlationwith statistical process 6: This IC includes overtemperature protection that is intended toprotect the device during momentary overload conditions.

8 Junctiontemperature will exceed 125 C when overtemperature protection is operation above the specified maximum operating junctiontemperature may impair device (V)0 ICC ( A)1001508372311 G0150024610200 Start-Up ICC vs VCCVCC vs ISHUNTO scillator Frequency vsTemperatureTYPICAL PERFOR A CE CHARACTERISTICS UWISHUNT (mA)0 VCC (V) ( C)FREQUENCY (kHz)24025080372311 G03230220 40 60 202004060100260CT = 270pF(TA = 25 C unless otherwise noted)Leading Edge Blanking Timevs RLEBVREF vs IREFVREF vs TemperatureRLEB (k )0 BLANK TIME (ns)350300250200150100500372311 G04401002010305070906080 IREF (mA)0 VREF (V) G05510203035TJ = 25 CTJ = 85 CTJ = 40 CTEMPERATURE ( C)VREF (V) 40 60 37211fsFREQUENCY (Hz)GAIN (dB)PHASE (DEG) 1801M372311 G07 270 360101k10010k100k10M100806040200 TEMPERATURE ( C) 55 ICC ( A)190180170160150140130120110100372311 G08 255359512565 RDPRG (k )050 DELAY (ns)1001502007512517522527550100 150 200372311 G09250500450400350300250NO 200k PREBIAS200k PREBIASTEMPERATURE ( C) 55 CURRENT ( A)9080706050403020100372311 G10 255359512565CT = 1 VCT = ( C) G11 255359512565 SHUNT VOLTAGE (V)

9 ICC = 10mAError Amplifier Gain/PhaseStart-Up ICC vs TemperatureTYPICAL PERFOR A CE CHARACTERISTICS UWDeadtime vs RDPRG(TA = 25 C unless otherwise noted)Slope Current vs TemperatureVCC Shunt Voltage vsTemperatureFB Input Voltage vs TemperatureTEMPERATURE ( C) 55FB VOLTAGE (V) G12 255359512565 LTC3721-16sn37211 37211fsVREF (Pin 1/Pin 15): Output of the Reference. VREF iscapable of supplying up to 18mA to external circuitry. VREF should be decoupled to GND with a 1 F ceramic (Pin 4/Pin 1): High Speed Sink, 1A SourceTotem Pole MOSFET Driver. Connect to gate of externalpush- pull MOSFET with as short a PCB trace as practicalto preserve drive signal integrity.

10 A low value resistorconnected between DRVA and the MOSFET gate is op-tional and will improve the gate drive signal quality if thePCB trace from the driver to the MOSFET cannot be (Pin 5/Pin 2): Supply Voltage Input to the LTC3721-1and Shunt Regulator. The chip is enabled after VCChas risen high enough to allow the VCC shunt regulator toconduct current and the UVLO comparator threshold isexceeded. Once the VCC shunt regulator has turned on,VCC can drop to as low as 6V (typical) and maintainoperation. Bypass VCC to GND with a high quality 1 F orlarger ceramic capacitor to supply the transient currentscaused by the high speed switching and capacitive loadspresented by the on chip totem pole (Pin 6/Pin 3): High Speed Sink, 1A SourceTotem Pole MOSFET Driver.