Page 22 - PEN eBook December 2022

DESIGN Design

CONVERTER OVERVIEW

The LLC resonant converter presented here features a primary full-bridge and a center-tapped
full-wave synchronous rectifier for the secondary, as shown in Figure 1 (left). Both are coupled with a

planar transformer having a 4:1 turns ratio. The power FETs used in the primary and secondary, together
with the transformer and printed-circuit boards, are the key components of the module. Figure 1 (right)
shows a photo of the overall module assembled.

eGaN FETs Enable More

Than 4-kW/in. Power
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Density for 48-V to

12-V Power Conversion

GaN transistors in a chip-scale package Figure 1: Topology of the LLC converter (left); photo of the assembled LLC power converter module (right)

enable higher than 4-kW/in. power density for POWER TRANSISTORS AND GATE DRIVERS
3

48-V to 12-V power conversion using an LLC For the primary circuit, four 100-V–rated 3.2-mΩ EPC2218s are used in conjunction with two
5
6
resonant converter with up to 1-kW capability. uP1966Es , a half-bridge gate-driver IC. For the secondary rectifier, a total of six 40-V–rated 1.55-mΩ
EPC2067s are used as synchronous rectifiers. These six transistors are divided into two branches,
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where each branch consists of an LMG1020 low-side gate driver controlling a parallel array of three
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By Alejandro Pozo, senior applications engineer at Efficient Power Conversion EPC2067s. All power transistors and gate drivers are in CSP format for minimum size and lowest
parasitic elements.
Growing computational power and miniaturization of electronics in computing and data centers
is increasingly putting pressure on 48-V power delivery and conversion systems. High-efficiency The choice of eGaN transistors is especially advantageous in the primary given the low R × C
DS(on) OSS
and high-power–density converters enable a reduction in power losses at the system level while figure of merit compared with equivalent Si MOSFETs. This is because for a similar R and voltage
DS(on)
allowing smaller form factors. In this context, LLC resonant topologies combined with GaN rating, GaN transistors offer lower C , therefore minimizing the magnetizing current needed to achieve
OSS
technology succeed to deliver outstanding performance, as it has been demonstrated with multiple ZVS in as short a transition time as possible. As a result, the frequency can be increased to the 1-MHz
examples. This article will show the key design parameters and components to achieve beyond range, enabling size reductions in the passive components while maintaining high efficiency.
1–4
4 kW/in. of power density in a 48-V to 12-V LLC converter using eGaN FETs. This work is an evolution
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of Reference 2 and was first introduced in Reference 1, demonstrating 96.3% peak efficiency and The uP1966E half-bridge gate drivers used for the primary are an ideal match for this application, in
93.8% when delivering 1 kW into a 12-V load and with module dimensions of 17.5 × 22.8 × 7.7 mm. which a minimum of 80-V rating and minimum size and external components are key features. Similarly,

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