Michael de Rooij & Yuanzhe Zhang Comparison of 6.78 MHz Amplifier Topologies for 33W, Highly Resonant Wireless Power Transfer Efficient Power

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1 Michael de Rooij & Yuanzhe Zhang Comparison of 6.78 MHz Amplifier Topologies for 33W, Highly Resonant Wireless Power Transfer Efficient Power Conversion Corporation

2 Agenda Wireless power trends AirFuel Class 4 High power capable amplifiers Experimental results Summary egan is a registered trademark of Efficient Power Conversion Corporation EPC The Leader in GaN Technology 2

3 Higher power Wireless Power Trends More devices needing wireless power Smartphones (~6 W) Tablets (~13 W) Small laptops (~25 W) Fast charging Move toward wireless power, not just charging EPC The Leader in GaN Technology 3

4 AirFuel Class 4 Operation A RMS into the coil or de-rated at 33 W 6.78 MHz Devices 1x Category 5 (20 W) up to 3x Category 3 (6.5 W) EPC The Leader in GaN Technology 4

5 AirFuel Class 4 Impedance Load Variation Arcs 50 Ω Smith Chart Full Load Arc j Ω j Ω On-Resonance Increasing Coil Enhancement Impedance Rotation permissible j Ω Tuned Coil j Ω Unloaded Coil Arc Increasing Coil Shunting EPC The Leader in GaN Technology 5

6 Wireless Power Amplifiers Differential mode ZVS class D + V DD Robust to load variations ZVS tank 1 Q 1 V DS I D L ZVS1 ILZVS C s I Coil Z load ZVS tank 2 L ZVS2 Q 3 Requires level shifting gate driver Q 2 C ZVS1 C ZVS2 Q 4 Differential mode class E V DD I RFck Simple and low cost + V DS L RFck I D C s Le1 I Csh Z load I Coil Le2 L RFck Susceptible to load variations Q 1 C sh1 C sh2 Q 2 EPC The Leader in GaN Technology 6

7 ZVS Class D Design Analytical design: -50j Ω through +50j Ω & 1 Ω through 52 Ω Optimal L ZVS and dead-time: EPC2007C (30 mω) = 390 nh, 8ns EPC8010 (160 mω) = 500 nh, 3.5 ns Requires synchronous bootstrap + V DD V / I Q 1 ZVS tank 1 I Coil ZVS tank 2 Q 3 V DD V DS V DS I D Q 2 L ZVS1 ILZVS C ZVS1 C s Z load L ZVS2 C ZVS2 Q 4 I LZVS I Coil 50% Ideal Waveforms I D time EPC The Leader in GaN Technology 7

8 V DD + V DS ID Class E Design Optimal load point analysis by simulation Realizable design FET selection: I RFck EPC2012C (100 mω), C sh = 68 pf EPC2019 (50 mω), C sh = 0 pf Le = 600 nh, L RFck = 39 µh L RFck C L s Z load L RFck e1 Le2 V DS V / I 3.56 x V DD I D Q 1 C sh1 I Csh I Coil C sh2 Q 2 I Coil time 50% Ideal Waveforms EPC The Leader in GaN Technology 8

9 Total FET loss [mw] Load Power [W] Class E Optimization LTSpice simulation: Total FET power loss Optimal load resistance lowest cumulative FET loss over entire Load resistance range Ω 40 Ω 46 Ω Pload Thermal limit R load [Ω] Optimal Load EPC The Leader in GaN Technology 9

10 Experimental Units ZVS class D Class E EPC2007C EPC2012C EPC8010 EPC2019 EPC The Leader in GaN Technology 10

11 Class D EPC2007C Thermally limited at extreme load impedances 60j Ω range class 4 capable EPC The Leader in GaN Technology 11

12 Class D EPC8010 Thermally limited at extreme load impedances 70j Ω range class 4 capable EPC The Leader in GaN Technology 12

13 Class E EPC2012C Thermally and voltage limited 25j Ω range class 4 capable EPC The Leader in GaN Technology 13

14 Class E EPC2019 Thermally and voltage limited 40j Ω range class 4 capable EPC The Leader in GaN Technology 14

15 Efficiency ranges all designs Class D - wide variation due to wider impedance range EPC The Leader in GaN Technology 15

16 Amplifier Performance Summary Class E performance nearly identical when compared over same impedance range Class D yields greater improvement from lower R DSon Topology egan FET (R DSon ) Efficiency Range at max. Power Reactance Range Relative Range ZVS class-d Class-E EPC % to 90.6% -35j to +35j Ω 70j Ω EPC2007C 87.5% to 92.8% -15j to +45j Ω 60j Ω EPC2012C 85.1% to 90.4% -20j to +5j Ω 25j Ω EPC % to 88.6% -20j to +20j Ω 40j Ω EPC The Leader in GaN Technology 16

17 Device Temperature [ C] Class E Limitations 160 V limit 80% of rated or 100 C Voltage limited Drain Voltage Coil Current j 0j EPC j Reflected Resistance [Ω] +5j Ω 0j -20j EPC2012C EPC The Leader in GaN Technology 17

18 Summary 33 W wireless power amplifiers compared Wider impedance range leads to lower cost systems ZVS Class D: 75% wider impedance range than class E Class E: Easier to drive and more popular egan FETs yield high efficiency at full power Lower R DSon improves performance but higher C OSS leads to Higher soft-switching energy for class D Design with negative C sh for Class E EPC The Leader in GaN Technology 18

19 The end of the road for silicon but a clear road ahead for GaN FETs and ICs!