GS-EVB-LLC-3KW-GSReference DesignGaN-Based 3KW Full Bridge LLC ResonantConverter Reference DesignTechnical ManualVisit for the latest version of this documentGS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com1

GS-EVB-LLC-3KW-GSReference DesignTable of Contents1.Scope and Purpose . 32.Introduction . 32.1System Block Diagram . 32.2System Specifications . 62.3Reference Design Board . 72.4Test Setup Procedure. 73.System Design Considerations . 83.1GaN-Based LLC Value Proposition . 83.2LLC Resonant Tank Design . 94.5.Test Results . 114.1Test Equipment . 114.2Efficiency . 125.1Load Regulation . 135.2Thermal . 145.3Electrical Waveforms. 14Conclusion. 18References . 19GS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com2

GS-EVB-LLC-3KW-GSReference Design1. Scope and PurposeThis document provides a general functional description and guideline to designing with the3KW LLC isolated DC/DC resonant converter reference design (GS-EVB-LLC-3KW-GS) based onthe 650V Gallium Nitride (GaN) transistor from GaN Systems. It describes the features, systemoperations, board setup procedure, and GaN-based LLC key parameters.2. IntroductionThe full bridge LLC resonant converter design, integrating GaN Systems’ 650V Enhancementmode transistors, exceeds the 80 Titanium standard for power supply units (PSUs), achievinghigh power density (AC/DC PSU) above 100W/inch3 and high efficiency of more than 96 percent.The key benefits and features of this GaN-based LLC include: High density: 146W/inch3 (including air-forced cooling) High efficiency: Peak efficiency 98% Small size: 30mm height and meets low profile 1U datacenter PSU form factor High switching frequency with maximum up to 450 KHz Comprehensive system protections such as over current, short circuit, and over voltageThis reference design is applicable to high-density AC/DC SMPS designs with galvanic isolation,for example, data center server, telecom, and industrial power supplies.2.1 System Block DiagramThe GS-EVB-LLC-3KW-GS reference design includes three main system blocks: the first block isthe full bridge LLC power stage; the second block is the digital-based MCU control whichincludes the signal sensing, algorithm processing, and control signal outputs for the power stage;and the third block is the auxiliary power supply to supply for the whole system such ascontroller, driver IC, and fan.Figure 1 illustrates the power stage block diagram for the 3KW LLC resonant converter. On theprimary side, there are two half bridge GaN boards (#1 & #2) building up a full bridge topology.Each GaN board implements one 650V, 50mΩ 8x8mm PQFN GaN transistor on both high sideand low side; the isolated gate drive ICs (Si8271AB) and isolated DC/DC converter are includedon the GaN boards to drive the GaN transistor. The isolated DC/DC converter converts 10VPGS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com3

GS-EVB-LLC-3KW-GSReference Designinput voltage to 5.8V and -3V for the GaN transistor turn-on and turn-off voltages respectively.The resonant tank (resonant inductor Lr, resonant capacitor Cr, and transformer Tr) are designedto achieve a resonant frequency at 250KHz and maximum switching frequency up to 450KHz.On the output side, the full wave synchronous rectification uses two 150V, 4.4mΩ silicon SRMOSFETs in parallel per switch to rectify the output to 54V.3KW Full Bridge LLC Converter Main BoardVBULKVin PrimarySecondaryVoVVDC/DC10VP5VPAUXPWMH1380V PWMH2650V 50mΩ8x8 PQFN GaNPGND Vo5.8V/-3VV2H650V 50mΩ8x8 PQFN GaNPQ3220Lr 15uHTrPQ4030Lm 75uH54VCr VV1LDC/DC10VP5VPAUXSi8271ABPWML2650V 50mΩ8x8 PQFN GaNGaN Board#1PGND5.8V/-3V15:2:2IPB044N15N5x2pcsV2L650V 50mΩ8x8 PQFN GaNIPRIGaN sCS re 1. Simplified power stage block diagram for the GS-EVB-LLC-3KW-GS reference designAs shown in Figure 2, the STM32F334C8 MCU is placed on the secondary side which includesthree key functional sections:1) Feedback signal sensing and sampling from power stage2) Digital control algorithm process3) Output signal generations for power stageThe feedback signal sensing and sampling circuits have the following sections:1. Output voltage sense (Vo sample) for control feedback loop algorithm;2. Primary input voltage sense (VBULK) with an optocoupler isolation from the primaryside to the secondary side, which acts as input voltage brown-out protection. The LLCresonant converter will not operate until the input DC voltage Vin is above 370V and shutdown when the input voltage is below 340V;GS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com4

GS-EVB-LLC-3KW-GSReference Design3. Primary current through the resonant tank (IPRI) senses for overcurrent protection (OCP)with an optocoupler isolation to secondary side signal, OCP pri. When the primarycurrent is above 18A, the primary OCP is triggered, and LLC resonant converter will shutdown;4. Secondary side current on the output (CS ) is sensed to MCU (OCP sec) for the outputOCP. When the output current is above 60A, the output OCP is triggered, and the LLCresonant converter will shut down.The digital control algorithm processing includes the state machine for the output load regulationand system protection. The control feedback algorithm regulates output voltage at 54V with inputvoltage range from 380V to 400V and load range from 0A to 55A. It also integrates the protectionwith the input voltage brown-out, primary OCP, and output OCP.The output drive signals (PWMH1/PWML1 and PWMH2/PWML2) are generated after the signalisolation (ISO7740) to drive the primary side’s GaN boards. The SR1 and SR2 are the secondarydrive signals for SR MOSFETs.3KW Full Bridge LLC Converter MCU BoardPrimarySecondarySR25VPAUXDOUTDHS/LSSR on-timeShoot-through OUTCclampprotectSR15VSDuty ClampSDGNDPWMH1FswOUTAOOUTBHS/LSDead timeISO7740 OUTAO Shoot-through OUTACal.protectPWML1PWMH2PWML2SDGNDPGNDMCU State Machine0.5FrequencyFreq Clamp-PI Vo S 3.3V VDAINA213DCKProtection/CTRPGOODOCP pri (HW)OCP sec (ADC)MCU enable &System SAGNDSAGNDFigure 2. MCU control block diagram for the GS-EVB-LLC-3KW-GS reference designThe auxiliary power supply block in Figure 3 uses a QR flyback topology with GaN Systems 650V450mΩ GaN transistor (GS-065-004-1-L), which gets 10VP output for primary supply voltage,10VS output for secondary supply voltage, and 12VSFAN output for air-forced fan.GS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com5

GS-EVB-LLC-3KW-GSReference Design3KW Full Bridge LLC Converter Auxiliary Power BoardPrimarySecondaryVin 10VS for system-10VP for systemSDGND PAUXPWRGND0ΩPWRGNDPGNDPGNDFigure 3. Auxiliary power supply block diagram for the GS-EVB-LLC-3KW-GS reference design2.2 System SpecificationsTable 1 summarizes the key parameters and performance for the GS-EVB-LLC-3KW-GS referencedesign.Table 1. Key parameters & performance of GS-EVB-LLC-3KW-GS reference designParameterInput DC Voltage (Vin)Output Voltage (Vo)Max. Output Power (Po)Full Load Output Current (Io)Resonant frequency (fr)Max. Switching frequency (fmax)PerformancePower DensityPCBA Board SizePeak EfficiencySystem ProtectionsGS-EVB-LLC-3KW-GS –TM Rev 202105Value380-420 V54 V3000 W55 A250 KHz450 KHzSpecification146 W/in380 mmx140 mmx30 mm(with air-forced cooling fan) 98%Input voltage brown-out, output short,output OCP, primary OCPwww.gansystems.com6

GS-EVB-LLC-3KW-GSReference Design2.3 Reference Design BoardFigure 4 shows the PCBA photo of this reference design which has a main power stage, two GaNboards (#1 & #2), one MCU board, and one auxiliary power board. A 15000 RPM fan is used tocool the heatsinks.Figure 4. PCBA photos for GS-EVB-LLC-3KW-GS reference design2.4 Test Setup ProcedureThe reference design board test setup procedure is as follows:1. Insert daughter boards (auxiliary power board, MCU control board, and GaN boards(#1) on the main board and make sure they are tightly connected with the main powerboard;2. Connect a DC source on the input side and an Electronic Load (E-load) on the output side;3. Apply a 300V DC at the input side, the fan will operate, and a Red LED on the MCU boardwill turn on, which means the auxiliary board is working;4. Set the E-load to CR (Resistor load) Mode and power up the board with no load or lightload;5. Increase the input voltage from 300Vdc to 400V; the output voltage will be about 54V;6. The board works and can be tested with the load increasing or decreasing.NOTE: PLEASE DO NOT APPLY DC INPUT VOLTAGE WITHOUT MCU BOARDGS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com7

GS-EVB-LLC-3KW-GSReference Design3. System Design Considerations3.1 GaN-based LLC Value PropositionThis GaN-based LLC resonant converter has several benefits due to its full resonant behaviorallowing soft switching turn-on over the entire range from no load to full load, which intrinsicallyhelps to minimize losses in both power transistors and magnetic components. In Figure 5, theLLC primary side current, ILr, consists of a superposition of the secondary side current, dividedby the transformer turns ratio n and the magnetizing current ILm. The magnetizing current doesnot transfer to the output but is required to discharge the parasitic output capacitance of thetransistors as well as a combination of the transformer intra-winding and inter-windingcapacitance, hence achieving Zero Voltage Switching (ZVS) for transistor turn-on withoutswitching turn-on loss. In order to achieve the ZVS for turn-on, the parasitic output capacitanceof the transistor should be fully discharged by using this magnetizing current during each deadtime. However, the magnetizing current will contribute an additional circulating loss on theprimary during the dead time. Minimizing magnetizing current is thus a goal for improving anLLC converter.ILrILmVdsILm pkVintdeadFigure 5. The primary current and voltage waveform for the LLC resonant converterThe minimum dead time tdeadmin for a full bridge LLC’s ZVS achievement condition can be derivedfrom equation (1) as the reference of [2]. Here, Lm is the magnetizing inductance of the maintransformer and fs is the switching frequency. From equation (1), the transistor parameter Co(tr),which describes the output capacitance needed to transition the drain to source voltage passively,is a key parameter for high efficiency and high-density LLC converters. The lower the value ofthe effective Co(tr), the less magnetizing current is required for a given drain to source transitionGS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com8

GS-EVB-LLC-3KW-GSReference Designtime, and this allows a higher value of magnetizing inductance for the transformer and a shorterdead time, lowering the circulating losses on the primary side. Meanwhile, for a given Lm andtdead, the lower value of effective Co(tr), the higher switching frequency fs can be used with ZVScondition to make a higher density.tdeadmin 8· Co(tr)·Lm·fs(1)Table 2. Key primary side transistors’ parameters for the LLC resonant converterAs shown in the Table 2, compared to Si and SiC, the GaN transistor with similar RDS(on) has lowervalues of Co(tr), Qgd, toff, and Qg, resulting in better performance of the LLC converter. Designed forhigh efficiency and high power density, especially with lower Co(tr), the shorter dead time isachieved with lower primary side circulation loss. In this 3KW LLC reference design, 100ns deadtime can be used with lower loss and maximum frequency up to 450KHz. On the contrary, a Sibased LLC should use longer dead time 200ns in order to achieve ZVS operation with typicalfrequency around 100KHz.3.2 LLC Resonant Tank DesignUsing the FHA (First Harmonic Approximation) method, the voltage DC gain can be theoreticallycalculated with reference to the equivalent resonant circuit, shown in Figure 6. This equivalentcircuit represents a transformation of the circuit, in which the output transformer and rectifier filter are reflected by an equivalent load Re, which is the output loading Ro of the convertertransformed back through the converter transformer and can be expressed in equation (2).GS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com9

GS-EVB-LLC-3KW-GSReference DesignLrCrVin acLmReVo acFigure 6. FHA equivalent resonant circuit and the DC gain M curve with frequencyRe( Ro) : 8p22 Nps Ro(2)Where Ro is the output load, Nps is the transformer’s turns ratio from primary to secondary.The mathematical expression (3) of the DC gain M is given in terms of switching frequency fand quality factor Qe:M ( f , Qe) : 1222éLr éfr ö ùùfr ö2æ fæê1 êúú 1-ç Qe ç - ë Lm ë è f ø ûûè fr f ø(3)Where:GS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com10

GS-EVB-LLC-3KW-GSReference DesignLrfr : 12 p Lr Cr ,Qe : CrRe( Ro)(4)The fr is resonant frequency and Qe is quality factor. Here, the Qe1, Qe2, Qe3, and Qe4 in Figure6 represent the quality factors at 100% full load, 10% load, 10x load, and 2x load respectively. TheLLC converter with wide load range is regulated to 54V with an input voltage range from 380Vto 420V. The resonant frequency is set at 250KHz. At 100% full load, the switching frequencyoperates from 220KHz to 280KHz. At light load or soft start-up conditions, the max frequency isup to 450KHz.The passive resonant tank values are designed with the following key parameters: Transformer Tr (ITG Electronics Inc. Part number: T301373SP-04)Ø Core: PQ4030 3C96 Lm 75µHØ Turns: 15:2:2TsResonant Inductor Lr (ITG Electronics Inc. Part number: L101374SP-03)Ø Core: PQ3220 3C96 Lr 15µHØ Winding: 0.1mm*200 15TsØ Distributed air-gapResonant Capacitor CrØ Cr 27nF4. Test ResultsThis section illustrates the testing equipment and experimental results of the reference design.4.1 Test EquipmentThe input power is measured by Power Meter (WT310E), output voltage is measured by MultiMeter (Fluke 179), and output current is measured by E-load (Chroma 63211).GS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com11

GS-EVB-LLC-3KW-GSReference DesignMulti-meterPower Meter Vin - VoDC sourceE-load-Figure 7. Test setup and equipment for GS-EVB-LLC-3KW-GS reference design4.2 EfficiencyThe efficiency curve and data are shown in the below figure and table. The efficiency data pointis measured after 10min soak time, and the auxiliary power loss is included, but the fan loss isexcluded. The efficiency result shows 98.2% peak efficiency at a half load 400V input. Theaverage efficiency (10%, 20%, 50%, and 100% loading) is above in91%420Vin90%020Io(A)4060Figure 8. Efficiency curve with output currentGS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com12

GS-EVB-LLC-3KW-GSReference DesignTable 3. Efficiency table with 380V, 400V and 420VVo (V)Io (A)Po 2354.26855.0562987.7790110%, 20%, 50%, 100% Average 32151.3704154.27855.0562988.3295710%, 20%, 50%, 100% Average 8.2587854.27355.052987.7286510%, 20%, 50%, 100% Average Eff.380Vin400Vin420VinPin 4%98.18%98.09%97.68%96.00%5.1 Load RegulationThe load regulation is within 54.0V 54.4V with wide load range and input voltage from 380V toVout(V)420V.Load in420Vin0.0020.0040.0060.00Io(A)Figure 9. Load regulation curve with output currentGS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com13

GS-EVB-LLC-3KW-GSReference Design5.2 ThermalThe thermal IR camera pictures and component temperatures are measured for 400V input anda full load operating condition after more than 0.5hr bake time. It shows that the GaN transistors’case temperature is below 80 C.Figure 10. Thermal IR image at 400V input and 3KW5.3 Electrical WaveformsFigures 11 to 13 show the steady state waveforms at 400V, 380V, and 420V input. The switchingfrequency is variable from 220KHz to 280KHz with different input voltage.Figure 14 is the load transient waveform from 10% load to 50% load and 50% load to 100% load.The peak-to-peak voltage is controlled within 3V during the load transient.Figures 15 and 16 show the start-up waveform at no load and full load. During the start-up, theswitching frequency starts from max 450KHz and gradually reduces to the regulated frequency.Figure 17 shows the output current protection waveform. The output OCP is triggered at 60Aoutput and the board is latched off. The main power must be cycled to restart the board.GS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com14

GS-EVB-LLC-3KW-GSReference DesignFigure 11. Steady state waveforms at 400V input and 10A, 25A, and 55A outputsFigure 12. Steady state waveforms at 380V input and 10A, 25A, and 55A outputsGS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com15

GS-EVB-LLC-3KW-GSReference DesignFigure 13. Steady state waveforms at 420V input and 10A, 25A, and 55A outputsFigure 14. Load transient waveforms at 400V inputGS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com16

GS-EVB-LLC-3KW-GSReference DesignFigure 15. No load startup waveforms at 380V, 400V, and 420V inputsFigure 16. Full load startup waveforms at 380V, 400V, and 420V inputsGS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com17

GS-EVB-LLC-3KW-GSReference DesignFigure 17. Output OCP waveform at 60A5.ConclusionThis GaN-based full bridge LLC resonant converter achieves the following best-in-class featuresand performance:§Topology:Full Bridge LLC resonant converter with synchronous rectifier§Power density:146W/in3§Height: 30mm§Efficiency: 98%§GaN Case Temp:80 CGS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com18

GS-EVB-LLC-3KW-GSReference DesignReferences[1] Design Considerations for a GaN-Based High Frequency LLC Resonant Converter [Online].Available: Design Considerations for a GaN-Based High Frequency LLC Resonant Converter- Technical Articles ([2] Investigation of High-density Integrated Solution for AC/DC Conversion of a DistributedPower System, Bing Lu, Virginia Polytechnic Institute and State University, PhD degreedissertation, May 2006Reference Design Important NoticeGaN Systems Inc. (GaN Systems) provides the enclosed reference design under the following AS IS conditions:This reference design is intended for use for ENGINEERING DEVELOPMENT, DEMONSTRATION, and OREVALUATION PURPOSES ONLY and is not considered by GaN Systems to be the design of a finished end-productfit for general consumer use. As such, the reference design provided is not intended to be complete in terms ofrequired design, marketing, and/or manufacturing-related protective considerations, including but not limited toproduct safety and environmental measures typically found in end products that incorporate such semiconductorcomponents or circuit boards. This reference design does not fall within the scope of the European Union directivesregarding electromagnetic compatibility, restricted substances (RoHS), recycling (WEEE), FCC, CE or UL, andtherefore may not meet the technical requirements of these directives, or other related regulations.No License is granted under any patent right or other intellectual property right of GaN Systems whatsoever. GaNSystems assumes no liability for applications assistance, customer product design, software performance, orinfringement of patents or any other intellectual property rights of any kind.www.gansystems.comImportant Notice – Unless expressly approved in writing by an authorized representative of GaN Systems, GaN Systems componentsare not designed, authorized or warranted for use in lifesaving, life sustaining, military, aircraft, or space applications, nor in productsor systems where failure or malfunction may result in personal injury, death, or property or environmental damage. The informationgiven in this document shall not in any event be regarded as a guarantee of performance. GaN Systems hereby disclaims any or allwarranties and liabilities of any kind, including but not limited to warranties of non-infringement of intellectual property rights. Allother brand and product names are trademarks or registered trademarks of their respective owners. Information provided hereinis intended as a guide only and is subject to change without notice. The information contained herein or any use of such informationdoes not grant, explicitly, or implicitly, to any party any patent rights, licenses, or any other intellectual property rights. General Salesand Terms Conditions apply.GS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com19

GS-EVB-LLC-3KW-GSReference Design 2009-2021 GaN Systems Inc. All rights reserved.GS-EVB-LLC-3KW-GS –TM Rev 202105www.gansystems.com20

operations, board setup procedure, and GaN-based LLC key parameters. 2. Introduction The full bridge LLC resonant converter design, integrating GaN Systems’ 650V Enhancement mode transistors, exceeds the 80 Titanium standard for power supply units (PSUs), achievingFile Size: 3MB