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The Growing Ecosystem for eGaN FET Power Conversion

The Growing Ecosystem for eGaN FET Power Conversion

May 18, 2019

Prologue

eGaN® FET-based power conversion systems offer higher efficiency, increased power density, and lower overall system cost than Si-based alternatives. These advantageous characteristics have spurred the presence of an ever-increasing ecosystem of power electronics components such as gate drivers, controllers, and passive components that specifically enhance eGaN FET performance. Some examples of eGaN FETs are shown in figure 1.

Examples of eGaN FETs
Figure 1: Examples of eGaN FETs ranging from 7 mΩ through 120 mΩ and from 100 V through 350 V

Overview of the eGaN FET ecosystem

The eGaN FET ecosystem can be broken down into three main categories: 1) gate driver, 2) controllers and 3) passive components. A typical synchronous buck converter, as shown in figure 2, highlights these various components. The requirements for these components are driven by the characteristics of eGaN FETs, such as small footprint, fast switching, tight gate voltage requirement, and high-frequency capability.

Circuit schematic of a typical synchronous eGaN FET based Buck converter
Figure 2: Circuit schematic of a typical synchronous eGaN FET based Buck converter, highlighting critical components in the eGaN FET ecosystem

Gate drivers for eGaN FETs

The gate driver IC is crucial for maximizing the switching speed capability of eGaN FETs. To be compatible with eGaN FETs, the gate driver must have a suitable UVLO for 5 V drive, low pull-up and pull-down resistances, small footprint, and isolation with sufficient common-mode transient immunity (CMTI) to withstand the high dv/dt. Other beneficial features of some eGaN compatible drivers include integrated voltage regulators, bootstrap management, and very narrow pulse width capability. Table 1 shows some examples of low side gate drivers suitable for use with eGaN FETs and table 2 similarly shows half-bridge gate drivers.

Manufacturer Part Number Includes LDO Key Feature Application Example
Texas Instruments LM5114 No General purpose Contact EPC
Texas Instruments UCC27611 Yes Suitable for use in a half bridge with a digital isolator EPC9081
Texas Instruments LMG1020 No Ultra-fast,1 ns pulse width Contact EPC
uPI uP1964 Yes Integrated adjustable drive voltage regulator
IXYS IXD_604 No Dual driver, suitable for large FETs
Table 1: eGaN FETs compatible low side gate drivers
Manufacturer Part Number Working Voltage (V) Bootstrap Management Input CMTI (V/ns) Application Example
Texas Instruments LM5113-Q1(NRND)*‡ 100 Yes Lo & Hi 50 EPC9078
Texas Instruments LMG1205*‡ 100 Yes Lo & Hi 50 EPC9078
uPI uP1966A*‡ 80 Yes Lo & Hi EPC9078
uPI uP1966B* 80 Yes PWM
pSemi PE29101 100 Yes PWM Contact EPC
pSemi PE29102 100 No PWM EPC9204
Texas Instruments LMG1210 200 Yes PWM 300 Contact EPC
Silicon Labs Si8274GB1-IM 630 No PWM 200 Contact EPC
Silicon Labs Si8275GB-IM 630 No Lo & Hi 200 Contact EPC
Analog Devices ADuM4120ARIZ 1092 V No Lo or Hi 150
Analog Devices ADuM4121ARIZ 1118 V No Lo or Hi 150
* Footprint compatible ‡ Pin compatible
Table 2: eGaN FET compatible half-bridge gate drivers

For high voltage designs where no single IC solution exists, low side gate drivers can be used in combination with high voltage signal isolators that feature high CMTI.

Controllers for eGaN FETs

As eGaN FETs push converters to higher frequencies, controllers are required to operate in the MHz range with higher control bandwidth and tighter regulation for high-frequency converters. Many controllers also incorporate a gate driver stage, which must meet the same gate driver requirements previously mentioned. Tables 3 and 4 show eGaN FET compatible controllers for synchronous rectification and synchronous Buck converter applications, respectively.

Manufacturer Part Number Gate Driver Included Activation / Deactivation time FET Voltage (V) DC Voltage (V)
NXP TEA1993TS Yes 65 ns / 40 ns 120 38
NXP TEA1995T Yes (Dual) 80 ns / 40 ns 100 38
NXP TEA1998TS Yes 40 ns / 40 ns 60 10.5
ON-Semi NCP4305A Yes 35 ns / 12 ns 200 35
ON-Semi NCP4308A Yes 40 ns / 20 ns 150 35
Table 3: eGaN FET compatible controllers for synchronous rectifiers
Manufacturer Part Number Gate Driver Included Operating Frequency Max. Duty Cycle Working Voltage (V)
Analog Devices LTC7800 Yes 320 kHz - 2.25 MHz 98% 60
Microchip MIC2127A Yes 270 kHz - 800 kHz 85% 75
Microchip MIC2103/4 Yes 200 kHz - 600 kHz 85% 75
Texas Instruments LM5140-Q1 Yes 440 kHz / 2.2 MHz 95.6% / 78% 65
Texas Instruments TPS40400 Yes 200 kHz - 2 MHz 95% / 75% 20
Texas Instruments TPS53632G No 300 kHz - 1 MHz 5
Renesas ISL8117A Yes 100 kHz - 2 MHz 60
Table 4: eGaN FET compatible controllers for synchronous buck converters

Digital controllers are also useful for many eGaN FET applications, such as multi-phase and multi-level architectures. Suitable examples include Microchip’s PIC series and TI’s Delfino and Piccolo series.

Passive components for eGaN FETs

The higher operating frequency of eGaN FET based converters requires passive components optimized for higher frequencies.

Key metrics in eGaN FET converter performance are power density and efficiency, which includes the input and output filters. Important inductor selection parameters include low series resistance (ESR) to minimize conduction loss, low core loss, and low parasitic capacitance. Vishay’s IHLP series are well suited to meet these criteria.

Suitable ceramic capacitor selection for the bypass/decoupling are available from multiple vendors where temperature coefficients of X7R or X7S offer excellent results with highest power density.

Conclusion

As eGaN FETs continue to penetrate application designs, the surrounding ecosystem of supporting components needed to achieve the superior performance of eGaN FETs will also grow. Today this ecosystem is no longer a limiting factor in GaN-based designs, and designers have a rapidly increasing number of gate drivers, controllers, and passive component options to choose from.

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