SM72295: Highly Integrated Gate Driver For 800VA To 3KVA .
Application ReportSNVA678B – September 2012 – Revised May 2013AN-2296 SM72295: Highly Integrated Gate Driver for800VA to 3KVA Inverter.ABSTRACTThis application note describes the design principles and circuit operation of TI’s highly Integrated Gatedriver in the Low Frequency Inverters.The inverter industry is expected to witness many technological innovations in the coming years to cater toa larger number of applications and new categories of end users. The demand from retail showrooms,small offices and residential use is primarily for 800VA, 1 kVA, 1.4 kVA and 2 kVA inverters. Being ahighly fragmented, competitive and growing market, it is in desperate need of constant Innovation andIntegration.123ContentsIntroduction . 21.1Basics of Gate Drive Requirement . 21.2Bootstrap circuit Principle for High Side Gate Drive . 31.3Low Frequency 600VA to 3KVA Pure Sine Wave Inverter Design . 4SM72295– Achieving High Integration in Current LF Inverter Design . 72.1Application Schematic — SM72295 in 800VA Pure Sine Wave Inverters . 82.2Easy Design Guidelines for Integrated Current Sensing . 92.3Layout Guidelines . 10Test Results in 850VA Pure Sine Wave Inverter Applications . 113.1Inverter Mode . 113.2Charger Mode/Mains Mode . 13List of Figures.Power MOSFET Gate Drive Characteristics .Bootstrap Supply Circuit .Inverter’s Block Diagram .Gate Drive Inputs in Inverter Mode .Inverter Mode Operation .Block Diagram of SM72295 Gate Driver .SM72295 in 800VA pure Sine Wave Inverters .Integrated Current Sensing Amplifier .Inputs to Gate Driver in Inverter Mode with Load of 700VA .1Simplified Model of a Non Inverting Gate Driver IC and a Power MOSFET22A Closer Look of Driver Driving the MOSFET234567891011345667891112Signal Integrity from Input to Output Gate Drives in Low Side MOSFETs on 700VA Load in InverterMode. . 1213Signal Integrity from Input to Output Gate Drives in High Side MOSFETs on 700VA Load in InverterMode . 1314Inputs to Gate Driver in Mains Mode With AC Mains Input of 220V . 1415Signal Integrity from Input to Output Gate Drives in Low Side MOSFETs in 220V AC Mains Mode. . 1416Signal Integrity from Input to Output Gate Drives in High Side MOSFETs in 220V AC Mains Mode. . 15All trademarks are the property of their respective owners.SNVA678B – September 2012 – Revised May 2013Submit Documentation FeedbackAN-2296 SM72295: Highly Integrated Gate Driver for 800VA to 3KVAInverterCopyright 2012–2013, Texas Instruments Incorporated1
Introduction1www.ti.comIntroductionGate Driver is a power amplifier that accepts a low-power input from a controller IC and produces theappropriate high-current gate drive for a power MOSFET. The gate driver must source and sink current toestablish required Vgs. A gate driver is used when a pulse width- modulation (PWM) controller cannotprovide the output current required to drive the gate capacitance of the MOSFET. Gate drivers may beimplemented as dedicated ICs, discrete transistors, or transformers. They can also be integrated within acontroller IC. Partitioning the gate-drive function off the PWM controller allows the controller to run coolerand be more stable by eliminating the high peak currents and heat dissipation needed to drive a powerMOSFET at very high frequencies.1.1Basics of Gate Drive RequirementDrainPower SourceFigure 1. Simplified Model of a Non Inverting Gate Driver IC and a Power MOSFETA Real MOSFET’s PropertiesFundamentally a voltage controlled switch.Inherent parasitic capacitors.Rds(ON) is not negligible.This leads to the requirement of Gate driver which must source and sink current to establish requiredthreshold voltage from Gate to Source Vgs.SW-NodeVCCDCGDDriverPWMPTurn OnNTurn OffGCDSCGSSMOSFETFigure 2. A Closer Look of Driver Driving the MOSFET2AN-2296 SM72295: Highly Integrated Gate Driver for 800VA to 3KVAInverterSNVA678B – September 2012 – Revised May 2013Submit Documentation FeedbackCopyright 2012–2013, Texas Instruments Incorporated
Introductionwww.ti.comVSG, Gate-To-Source Voltage (V)Figure 1 shows the simplified model, including the parasitic components that influence high-speedswitching, gate-to-source capacitance (CGS), the gate-to-drain capacitance (CGD), and drain-to-sourcecapacitance (CDS).Values of the source inductance (LS) and drain inductance (LD) depend on theMOSFET’s package. The other parasitic component is RG, the resistance associated with the gate signaldistribution within the MOSFET that affects switching times. An important attribute for the gate driver is itsability to provide sufficient drive current to quickly pass through the Miller Plateau Region of the powerMOSFET’s switching transition. This interval occurs when the transistor is being driven on or off, and thevoltage across its gate-to-drain parasitic capacitor (CGD) is being charged or discharged by the gatedriver. Figure 3 plots total gate charge as a function of the gate-drive voltage of a power MOSFET. Totalgate charge (QG) is how much must be supplied to the MOSFET gate. to achieve full turn-on. It is usuallyspecified in nanocoulombs (nC).QG, Total Gate Charge (nC)Figure 3. Power MOSFET Gate Drive Characteristics1.2Bootstrap circuit Principle for High Side Gate DriveThe gate drive requirements for a power MOSFET utilized as a high side switch, in applications like Fullbridge, half-bridge converters or synchronous buck converters can be summarized as follows: Gate voltage must be 6 to 12V higher than the source voltage. To fully enhance a high side switch, thegate to source voltage would have to be higher than the threshold voltage plus the minimum necessaryvoltage to fully enhance the MOSFET The gate voltage must be controllable from the logic level, which are normally referenced to ground.Thus, the control signals need to be level shifted to the source terminal of high side MOSFET (HSnode), which in most applications, swings between ground and the high voltage rail.The Bootstrap supply technique is a simple, cost-effective way to power the upper MOSFET’s gate andprovide bias supply to the floating logic sections of the Gate Driver. Only two components (a Bootstrapdiode and capacitance) per bridge phase are needed to implement the Bootstrap supply.SNVA678B – September 2012 – Revised May 2013Submit Documentation FeedbackAN-2296 SM72295: Highly Integrated Gate Driver for 800VA to 3KVAInverterCopyright 2012–2013, Texas Instruments Incorporated3
Introductionwww.ti.comRBootDBootDC SupplyBootstrap Charge Current PathBootstrap Discharge Current e 4. Bootstrap Supply CircuitUsing this circuit, the Bootstrap Capacitor is charged to ground through the Low side FET. When the Lowside FET is turned off, the bottom of the capacitor flies up and this creates a voltage greater than Vcc.This voltage is applied to the High side gate driver.1.3Low Frequency 600VA to 3KVA Pure Sine Wave Inverter DesignThere is a dual mode of operation in a residential Inverter ie Mains mode and Inverter mode. As shown inFigure 5, the Input AC voltage is fed to the transformer through a switch (relay). In the mains mode, wheninput AC is present and is within valid range, the switch is closed and the input AC directly goes to theoutput load. The same AC is fed to transformer, and the H-bridge consisting of MOSFETs or IGBTs aredriven through microcontroller or DSP to charge the battery. A bridge less rectification principle is used tocharge the battery by boosting the voltage produced in the transformer primary using the inductance of thewinding, by switching the lower MOSFET banks. The lower MOSFET switches are switched and upperswitches kept turned OFF, The body diodes of the upper MOSFETS will act as rectifiers. The pulse widthof the switching pulses of the lower bank is proportional to the output charge current.4AN-2296 SM72295: Highly Integrated Gate Driver for 800VA to 3KVAInverterSNVA678B – September 2012 – Revised May 2013Submit Documentation FeedbackCopyright 2012–2013, Texas Instruments Incorporated
Introductionwww.ti.comMains InputInverter SectionPower StagePower Transformer5 T1 1C2BatteryBank34SwitchOutputLoadDSP ControlFigure 5. Inverter’s Block DiagramThe DC/AC inversion can be achieved using any one of the two following methods.The method in which the low voltage DC power is inverted, is completed in two steps. The first is theconversion of the low voltage DC power to a high voltage DC source, and the second step is theconversion of the high DC source to an AC waveform using pulse width modulation.Another method to complete the desired outcome would be to first convert the low voltage DC power toAC, and then use a transformer to boost the voltage to 120/220 volts. The widely used method in thecurrent residential inverter is the second one . Here if the AC fails or is out of valid range (AC VoltageSense is required), the switch between Mains Input and Output Load opens. H-bridge circuit convertsbattery DC voltage into AC using high frequency PWM (5 kHz to 15 KHz) thus feeding the sametransformer which is being used for charging in the mains mode. The output of transformer contains acapacitor which filters it to make 50 Hz AC.SNVA678B – September 2012 – Revised May 2013Submit Documentation FeedbackAN-2296 SM72295: Highly Integrated Gate Driver for 800VA to 3KVAInverterCopyright 2012–2013, Texas Instruments Incorporated5
Introductionwww.ti.comINV O/PBatterySwitchLInputAC N1 T1 5C248W BridgeBAT 15Three Level PWM SignalQ1D1510D2Q3BatteryBT10T1Q2D31 C158D4Q44-5RSENSEINV O/P-10-1500.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018Figure 6. Gate Drive Inputs in Inverter ModeBAT OFFPWMPWMQ1D15D2Q3OFFBatteryBT18T1Q2D31 C1D44INV O/PONQ4RSENSEComplementary PWMComplementary PWMONFigure 7. Inverter Mode OperationFor the Positive Half of the Sine Wave generation, Q2 is always high ,Q1 is always off , Q3 is applied with6.4KHz (6.4KHz to 20KHz) PWM corresponding to Positive Half cycle 50Hz sine wave and Q4 is appliedwith corresponding complementary (to Q3) PWM . For the Negative Half 50Hz sine wave generation , Q4is always high , Q3 is always off , Q1 is applied with 6.4KHz PWM corresponding to positive half cycle50Hz sine wave and Q2 is applied with Q1's complementary PWM .6AN-2296 SM72295: Highly Integrated Gate Driver for 800VA to 3KVAInverterSNVA678B – September 2012 – Revised May 2013Submit Documentation FeedbackCopyright 2012–2013, Texas Instruments Incorporated
SM72295– Achieving High Integration in Current LF Inverter Designwww.ti.com2SM72295– Achieving High Integration in Current LF Inverter Design100V Bootstrap DiodeVCCBHIBHIALIBLIAThe SM72295 is a full bridge MOSFET driver with 3A (higher no. of FETs in parallel for high power) peakcurrent drive capability with1. Integrated ultra fast 100V boot strap diodes (can easily support up to 5KVA rated inverters)2. Two high side current sense amplifiers with externally programmable gain and buffered outputs whichcan be used for measuring the Battery charge and discharge current – Additional current senseamplifiers and buffers are not required3. Programmable over voltage protection – which can be used for Charge complete detection or for drivershutdown feature in case of a fault condition4. Can be directly interfaced with a FTHSB100V Bootstrap IVER PGNDVDD 3.3V/5V-SIASIBIntegrated Current SensingAmplifiers SOBSOA IINIOUT VDDCLAMPVDDCLAMPBOUTAGNDBINFigure 8. Block Diagram of SM72295 Gate DriverSNVA678B – September 2012 – Revised May 2013Submit Documentation FeedbackAN-2296 SM72295: Highly Integrated Gate Driver for 800VA to 3KVAInverterCopyright 2012–2013, Texas Instruments Incorporated7
8AN-2296 SM72295: Highly Integrated Gate Driver for 800VA to R12499ER21R11499ECopyright 2012–2013, Texas Instruments 15 499EANR271MHOBHOAAND512VVCCBattery R20 1KR19220EShutdown signal from microcontrollerAll the outputs will be disabled if voltage atOVS VDD ie 3.3V in this caseSDHSBLOBLOAHSAAPR28 100KC15 0.47µFC14 0.47µFR18 499E1mE/2WBIN Discharging current in inverter mode (Gain R33/R11)BOUT Charging current in mains mode (Gain R34/R15)Both the current sense can directly be interfaced to the ADC of SIBVCC2VCC1U3SM72295APC32200µF/35VVCC1µF C12 0.1µFC11C42200µF/35V0.1µF 11 BOUT4151067891217VDDC10C52.2µF/35VBLIBattery -Battery H Bridge Switching Waveform Inputsgenerated by R4010ER3947ECSD18532KCS 532KCS2.1J1Battery FUSE140ASM72295– Achieving High Integration in Current LF Inverter Designwww.ti.comApplication Schematic — SM72295 in 800VA Pure Sine Wave InvertersFigure 9. SM72295 in 800VA pure Sine Wave InvertersSNVA678B – September 2012 – Revised May 2013Submit Documentation Feedback
SM72295– Achieving High Integration in Current LF Inverter Designwww.ti.com2.2Easy Design Guidelines for Integrated Current SensingIn the Inverter design, the charge current during the Mains mode and discharge current during the invertermode is needed to be measured and given to the ADCs of microcontroller or DSP.In SM72295, Current sensing is provided by two transconductance amplifiers with externallyprogrammable gain and filtering to remove ripple current to provide average current information to thecontrol circuit. The current sense amplifiers have buffered outputs available to provide a low impedanceinterface to an A/D converter.VSENSEISENSESIA INSOARSENSEDrop Across Ris VSENSEVDDCLAMPLOADRRSIA SOA VoltageSource Current Through FETis VSENSE/RBINP Channel FETCurrent SenseAmplifierIOUTBOUTV0 (VSENSE*R0)/R R0 VDDCLAMPSIBShuntDischargeBPIDischargeCurrent SignalRD2RD1SOBIOUTSIBRC2RC1SOAGain RD2/RD1ChargeCurrent SignalRC1SIAOUTChargeRD1IINSOBLOAD/ChargerGain RC2/RC1Figure 10. Integrated Current Sensing AmplifierSNVA678B – September 2012 – Revised May 2013Submit Documentation FeedbackAN-2296 SM72295: Highly Integrated Gate Driver for 800VA to 3KVAInverterCopyright 2012–2013, Texas Instruments Incorporated9
SM72295– Achieving High Integration in Current LF Inverter Designwww.ti.comHence the charge and the discharge current can easily be measured by giving individual gain to each ofthem. The charging current is generally pretty less than the possible Discharging current in 800VA LowFrequency inverter. The Maximum charging current for 150-165AH battery is close to 15A while thedischarging current can goes upto 60A-70A.2.2.1Steps of Current Sense Design1. Current Sense Resistance is chosen based on Max current and respective power dissipation onCurrent Sense resistance. In this Design, two 2W 1 milliohm resistances in parallel were chosen sothat even at 70A Discharge current in Inverter mode, the power dissipation is 2.45W which is muchlesser than allowed 4W(2W each of parallel 1milliohm Resistance).2. There is VDD (3.3V) clamped at the Current Sense amplifier output and hence the gain should bemaintained in such a way that the output is not clamped in the area of interest. The Discharge currentgain is achieved through R33 / R11 (refer to application Schematic) which comes out to be the gain of78 in this application. Even at 70A discharge current, the BIN 2.73V which is lower than VDD clamp.3. Since the Maximum Charge current in this application is close to 15A, the gain of this section ismaintained higher through R34/R15 ratio.2.3Layout GuidelinesThe optimum performance of high and low-side gate drivers cannot be achieved without taking dueconsiderations during circuit board layout. Following points are emphasized.1. Low ESR / ESL capacitors must be connected close to the IC, between VDD and VSS pins andbetween the HB and HS pins to support the high peak currents being drawn from VDD during turn-onof the external MOSFET.2. To prevent large voltage transients at the drain of the top MOSFET, a low ESR electrolytic capacitormust be connected between MOSFET drain and ground (VSS).3. In order to avoid large negative transients on the switch node (HS pin), the parasitic inductances in thesource of top MOSFET and in the drain of the bottom MOSFET (synchronous rectifier) must beminimized.4. Grounding Considerations(a) The first priority in designing Grounding Consideration is a part in layout Guidelines. connections isto confine the high peak currents that charge and discharge the MOSFET gate into a minimalphysical area. This will decrease the loop inductance and minimize noise issues on the gateterminal of the MOSFET. The MOSFETs should be placed as close as possible to the gate driver.(b) The second high current path includes the Bootstrap capacitor, the Bootstrap diode, the localground referenced bypass capacitor and low-side MOSFET body diode. The Bootstrap capacitor isrecharged on a cycle-by-cycle basis through the Bootstrap diode from the ground referenced VDDbypass capacitor. The recharging occurs in a short time interval and involves high peak current.Minimizing this loop length and area on the circuit board is important to ensure reliable operation.10AN-2296 SM72295: Highly Integrated Gate Driver for 800VA to 3KVAInverterSNVA678B – September 2012 – Revised May 2013Submit Documentation FeedbackCopyright 2012–2013, Texas Instruments Incorporated
Test Results in 850VA Pure Sine Wave
1.3 Low Frequency 600VA to 3KVA Pure Sine Wave Inverter Design . 9 SM72295 in 800VA pure Sine Wave Inverters . The Bootstrap supply technique is a simple, cost
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Gate Driver Providing Galvanic isolation Series. Isolation voltage 2500Vrms. 1ch Gate Driver Providing Galvanic . Isolation BM6104FV-C. General Description. The BM6104FV-C is a gate driver with isolation voltage . 2500Vrms, I/O delay time of 150ns, and minimum input pulse width of 90ns, and incorporates the fault signal
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