Application Note: TDPS251E0D2 LLC DC/DC … LLC DC/DC Converter Evaluation Board 1. Introduction The Evaluation Board for an LLC circuit using GaN HEMTs is described in this paper

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Application Note:

TDPS251E0D2 LLC DC/DC Converter Evaluation Board

1. Introduction

The Evaluation Board for an LLC circuit using GaN HEMTs is described in this paper. In this

board, Transphorm GaN power HEMTs with low reverse-recovery charge and low output

capacitance are used in a diode-free halfbridge to realize DC-DC voltage conversion with high

efficiency. The performance and efficiency improvement achieved by use of the GaN HEMTs in

the primary side of the LLC circuit is further enhanced by use of synchronous rectification in the

secondary side. The evaluation board is shown in Fig. 1.

Fig. 1. LLC DC/DC converter Evaluation Board

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2. TDPS251E0D2 Input/output Specifications:

• Input: 385 – 395 Vdc;

• Output: 12Vdc at 20A;

• PWM Frequency: 170kHz to 250 kHz

• Auxiliary Supply(12Vdc for bias voltage): The board is optimized for this bias voltage;

please provide 12V exactly for the best performance.

3. Circuit Description for LLC DC-DC Converter based on GaN HEMT

Figure 2 illustrates the topology of the evaluation board, which is based on the NCP1397 and

NCP4304 controllers. The series capacitor forms the series-parallel resonant tank with leakage

and magnetic inductances in the primary side of the transformer. From this configuration, the

resonant tank and the load on the secondary side, act as a voltage divider. By changing the

frequency of input voltage, the impedance of resonant tank will change; this impedance will

divide the input voltage with load. The primary-side switches, M1 and M2, are the GaN HEMTs.

Transistors S1 and S2 on the secondary side are synchronous rectifiers to improve the

performance and efficiency. As may be seen in Fig. 2, there is no need for special gate drivers

for the GaN HEMTs. Further information and discussion on the fundamental circuit schematics

and the characteristics of LLC DC-DC converters are provided in [1-3].

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Fig .2. Circuit topology for LLC DC-DC converter using silicon MOSFETs for line rectification

Although the LLC is a resonant topology, characterized by soft switching, hard switching does

nevertheless occur during start up. During this phase, the large reverse recovery charge (Qrr) of

typical silicon MOSFETs causes problematic overshoot, ringing, and loss.The Industry’s 1st

qualified 600-V GaN HEMTs made on low-cost Si substrate have been announced by

Transphorm Inc. These 1st-generation GaN power devices show a low on-resistance of 0.29 ohm

typical and are capable of reverse conduction during dead time with a low Qrr of 29nC, more

than 20 times lower than state-of-the-art Si counterpart as seen in Fig. 3. These features can

remarkably improve the performance and efficiency of hard-switch circuits, and also, it is

important for hard start in resonant circuits such as the LLC topology.

390V

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Fig.3Reverse recovery charge test result for a Si MOSFET and a GaN HEMT with similar on resistance,

showing a 20x reduction of Qrr for GaN.

Table 1 gives a comparison of CoolMOS and GaN HEMT. The low Qrr will help reducing

excessive spikes during start-up process in a LLC dc-dc converter.

Table 1: Comparison of GaN HEMT with equivalent CoolMOS IPP60R380C6

Parameter TPH3002PS IPP60R380C6

ID 9A (continuous) 10.6A (for D=0.75)

Ron 290mΩ 340mΩ

Qg 6.2nC 32nC

Eoss(400V) 3.1uJ 2.8uJ

Qrr 29nC 3.3uC

This evaluation board is designed to demonstrate Transphorm GaN HEMTs performance for a

LLC DC/DC converter application. The switch used for this board is the TPH3002PS (600V,

0.29ohmGaNHEMT). The circuit schematic and bill of materials are shown in Fig. 4and Table.2

respectively.

Si MOSFET GaN

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Fig.4. LLC DC/DC Converter Evaluation Board Circuit Schematics

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Table 2. Bill of Materials for the LLC DC/DC Converter Evaluation Board

Qty Value Device Package Parts Manufacturer Manufacturer P/N

1 connector FCI-20020316-2P FCI_20020316-

2P CN1 FCI

20020316-

G021B01LF

2 1.7mOhm OPTIMOS_PG-

TDSON-8 PG-TDSON-8 Q3, Q4

Infineon

Technologies BSC017N04NS G

6 .1u C-EUC0805 C0805 C8, C12, C13,

C20, C27, C29 AVX 08053C104KAT2A

3 .1u C-EUC1812 C1812 C2, C3, C4 Kemet C1812V104KDRAC

TU

1 2k R-US_R0805 R0805 R13 Panasonic ERJ-6ENF2001V

2 0R56 R-US_R0805 R0805 R28, R29 TE Connectivity 6-1622825-2

1 4.32k R-US_R0805 R0805 R8 Panasonic ERJ-6ENF4321V

1 100 R-US_R0805 R0805 R23 Panasonic ERJ-6ENF1000V

6 100u C-EUC1210 C1210 C30, C31, C32,

C33, C34, C35 Taiyo Yuden

EMK325ABJ107MM

-T

1 100u CPOL-USE2.5-7 E2,5-7 C9 RubyCon America 16PX100MEFCTA5

X11


1 10u C-EUC0805 C0805 C15 TDK C2012X5R1V106M0

85AC

1 11.0k R-US_R0805 R0805 R19 Vishay CRCW080511K0FK

EA

1 11v MMSZ5241 SOD123 D2 On Semiconductor MMSZ5241BT1G



EA


EA


2 1k R-US_R0805 R0805 R14, R17 Vishay CRCW08051K00FK

EA

1 1nF C-EUC0805 C0805 C18 Kemet C0805C102K5RACT

U

4 1u C-EUC0805 C0805 C10, C14, C26,

C28 Yageo

CC0805ZRY5V8BB1

05


1 2.2n C-EUC0805 C0805 C17 AVX Corporation 08053A222JAT2A

2 20k R-US_R0805 R0805 R24, R26 Panasonic ERJ-6GEYJ203V

1 22-23-2021 22-23-2021 22-23-2021 X1 Molex 22232021



1 332 R-US_R0805 R0805 R21 Stackpole RMCF0805FT332R

1 4.7 R-US_R0805 R0805 R5 Panasonic ERJ-6GEYJ4R7V


3 4.7n C-EUC1206 C1206 C5, C6, C7 Kemet C1206C472KDRAC

TU

2 4.7u C-EUC0805 C0805 C11, C16 TDK C2012X5R1H475K1

25AB

1 4.7u PHE450-886MIL PHE450-

886MIL C1 Panasonic ECW-FD2W475J

2 470uF 25V CPOL-USE5-10.5 E5-10,5 C36, C37 Panasonic EEU-FM1E471

2 5.9k R-US_R0805 R0805 R25, R27 Panasonic ERJ-6ENF5901V

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1 68n C-EUC0805 C0805 C19 Kemet C0805C683K5RACT

U


2 0.375" D-PAK

HEATSINK 7106DG_SHORT

7106DG_SHO

RT HS2, HS3

AAVID

THERMALLOY 7106DG

1 750 R-US_R0805 R0805 R16 Panasonic ERJ-6ENF750DV

3 953k R-US_R0805 R0805 R1, R2, R3 Vishay CRCW0805953KFK

EA

1 3300pF C-USC1206 C1206 C21 TDK CGA5LC0G2J332J16

0AA

4 4700pF C-USC1206 C1206 C22, C23, C24,

C25 TDK

CGA5F4C0G2J472J0

85AA


1 ES1J-LTP DIODE-DO-

214AC DO-214AC D1

Micro Commercial

Co ES1J-LTP

1 HCPL-817-50AE HCPL-817 DIL4-SMD U3 Avago HCPL-817-50AE

2 KEYSTONE_769

1_SMALLPAD

KEYSTONE_7691

_SMALLPAD

KEYSTONE_7

691_SMALLP

AD

J2, J3 Key Stone 7691

1 240W, LLC

XFMR, 12V/10A,

LLCDEMO_LAR

GEDIA2

LLC_LARGE

DIA2 Transformer Precision 019-7896-00R

1 NCP1397B NCP1397 SOIC16N-13 U1 On Semiconductor NCP1397BDR2G

2 NCP4304B NCP4304 SO-08 U2, U4 On Semiconductor NCP4304BDR2G

2 60ohm Ferrite

Bead R-US_R0603 R0603 R30, R31 TDK MMZ1608Y600B

1 TL431 TL431 SOT23 U5 NXP

Semiconductors TL431IDBZR,215

2 TPH3002S TPH3002PS TPH3002PS Q1, Q2 Transphorm TPH3002PS

While a typical Si MOSFET has a maximum dV/dt rating of 50V/ns, the Transphorm GaN

HEMT will switch at dV/dt of 100V/ns or higher. At this level of operation, even the layout

becomes a significant contributor to performance. As shown below, in Fig. 5-7, the

recommended layout keeps a minimum gate drive loop; it also keeps the traces between the

switching nodes very short, with the shortest practical return trace to power ground. As the

power ground plane provides a large cross sectional area to achieve an even ground potential

throughout the circuit. The layout carefully separates the power ground and the IC (small signal)

ground, only joining them at the source pin of the HEMT to avoid any possible ground loop.

Note that the Transphorm GaN HEMTs in TO220 package has pin out configured as G-S-D,

instead of traditional MOSFET’s G-D-S arrangement. The configuration is designed with

thorough consideration to minimize the Gate-Source driving loop to reduce parasitic inductance,

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as well as to separate the driving loop (Gate-Source) and power loop (Drain-Source) to minimize

noise. For further information, different layers of TDPS251E0D2 design are shown in Fig. 5-7.

Fig. 5. LLC DC/DC converter Evaluation Board Layout, Top Layer

Fig. 6. LLC DC/DC converter Evaluation Board Layout, Bottom Layer

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Fig. 7. LLC DC/DC converter Evaluation Board Layout, Middle Layers

Startup sequence:

1) Connect a load; The load should be resistive, and maximum of240watt at 12Vdc;

2) Connect the12 Vdc auxiliary supply (The dc adaptor);

3) With power off, Connect the high-voltage DC power input with polarity

corresponding to the marking on the PCB;

4) Place a cooling fan facing the GaN HEMTs heat sink (provide a minimum of 30 CFM

air flow);

5) Enable 12 Vdc bias by powering up the auxiliary supply;

6) Turn on the cooling fan;

7) Turn on the dc power input to 390Vdc.

Turn off sequences:

1) Switch off the high-voltage dc power input;

2) Power off dc bias;

3) Turn off the fan.

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Probing: In order to minimize additional inductance during measurement, the tip and the ground

of the probe should be directly attached to the sensing points to minimize the sensing loop; while

the typical long ground lead should be avoided since it will form a sensing loop and could pick

up the noise. An example of low inductance probing is shown in Fig 8.

Fig. 8. The voltage probing on the primary side for LLC DC/DC converter board

Efficiency has been measured at 390Vdc input and 12Vdc output using the WT1800 precision

power analyzer by Yokogawa. The results for this LLC DC/DC converter are shown in Table. 3,

and Fig. 9. The peak efficiency is more than 97%,which is noticeably better than competitor LLC

boards with Si switches; this high efficiency will enable customers to reduce system loss for

more compact designs in addition to more efficient energy usage.

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Table 3. The power and efficiency result for LLC board at 390Vdc input and 12Vdc output

Pin (W) Pout (W) Ploss (W) Eff (%)

32.46 30.86 1.60 95.06

63.28 61.34 1.94 96.93

95.87 93.36 2.51 97.39

128.00 124.75 3.25 97.46

158.31 154.16 4.15 97.38

188.39 183.16 5.24 97.22

220.13 213.45 6.67 96.97

250.16 241.86 8.30 96.68

Fig. 9. The efficiency result for LLC DC/DC Converter Board at 390Vdc input to 12Vdc output

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WARNING: There are no specific current or voltage protection on this board; users need to

follow the test procedure and operation limits carefully. Please refer to application note AN0002

and AN0003 for further information.

REFERENCES:

[1]. Robert L. Steigerwald, “A Comparison of Half-bridge resonant converter topologies,” IEEE

Transactions on Power Electronics, Vol. 3, No. 2, pp. 174-182, April 1988.

[2]. Bo Yang, F.C. Lee, A.J. Zhang, H. Guisong, "LLC resonant converter for front end DC/DC

conversion" Proc. IEEE APEC’02, pp.1108 – 1112, 2002.

[3]. B. Lu, W. D. Liu, Y. Liang, F. C. Lee, and J. D. VanWyk, “Optimal design methodology for

LLC resonant converter,” Proc. IEEE APEC’06, pp. 19–23, 2006.

Documents

Application Note: TDPS251E0D2 LLC DC/DC … LLC DC/DC Converter Evaluation Board 1. Introduction The Evaluation Board for an LLC circuit using GaN HEMTs is described in this paper