Ti Figure 1 Web 5faebe73852c1

Automotive GaN FET Features Integrated Driver

Nov. 13, 2020
The device, developed by Texas Instruments, is said to double power density and boost efficiency in automotive onboard chargers

Wide-bandgap semiconductors are an attractive material for power devices due to low losses, improved temperature capability, and high thermal conductivity. Compared to silicon (Si), with a larger bandgap, higher breakdown field, and higher electron saturation velocity, power devices can have higher breakdown voltage and operate at higher frequency.

In the automotive space, GaN FETs can help significantly reduce the size of electric-vehicle (EV) onboard chargers and dc-dc converters compared to existing Si solutions. As a result, engineers are able to achieve extended battery range, increased system reliability, and lower design cost.

Texas Instruments’ (TI) new 650- and 600-V automotive-qualified GaN FETs aim to power on-board charging systems in electric vehicles while reducing power losses by 50%. The parts are further said to help engineers deliver twice the power density, achieve 99% efficiency, and reduce the size of power magnetics by 59% compared to existing solutions.

One key advantage of GaN is fast switching, which enables smaller, lighter, and more efficient power systems. TI’s LMG342xR030 integrates a silicon driver that enables switching speed up to 150 V/ns. This integration, combined with a low inductance package, is said to deliver cleaner switching and minimal ringing in hard-switching power-supply topologies.

The integrated driver solves a number of other challenges in GaN applications. It ensures the device stays off for high drain slew rates. The driver also helps protect the GaN device from overcurrent, short-circuit, undervoltage, and overtemperature conditions with fault indication.

What’s more, the GaN FETs include adjustable gate-drive strength for EMI control, digital temperature reporting, and TI’s ideal diode mode. The latter maximizes efficiency by reducing third-quadrant losses via adaptive dead-time control and automatically realizes a fast synchronous FET operation without external circuitry.

Traditionally, when designing GaN FETs, engineers must solve the tradeoff between switching speed and power losses. TI’s ideal diode mode aims to reduce third-quadrant losses by up to 66% compared to discrete GaN and SiC MOSFETs. Third-quadrant operation can be defined as follows: When the GaN device is turned off and negative current pulls the drain node voltage to be lower than its source, the voltage drop across the GaN device during third-quadrant operation is high.

This integration, plus the high power density of GaN technology, enables engineers to eliminate more than 10 components typically required for discrete solutions, according to TI. In addition, each of the new 30-mΩ FETs can support up to 4 kW of power conversion when applied in a half-bridge configuration

The converter requires only a single surface-mount power inductor and output bypass capacitor. It’s designed to use a 4.7-µH inductor and a 2.2-µF output capacitor.

One aspect of a GaN converter is the reverse-recovery characteristic, which helps to avoid losses and other associated problems. Unlike Si MOSFETs, there is no p-n junction from source to drain in GaN devices. That’s why the GaN device can offer zero reverse recovery and a low output capacitance, enabling higher efficiency in bridge-based topologies.

GaN’s fast switching speed increases efficiency, which in turn reduces the burden on cooling in automotive vehicles. With packaging that allows engineers to use smaller heat sinks while simplifying thermal designs, the new devices provide thermal design flexibility with the ability to choose from either a bottom- or top-side-cooled package. In addition, the FETs’ integrated digital temperature reporting enables active power management. As a result, engineers can optimize system thermal performance under varying loads and operating conditions.

Pre-production versions of TI’s four new 600-V GaN FETs are available now, in a 12- × 12-mm, quad flat no-leads (QFN) package. Pre-production versions of the new LMG3522R030-Q1 and LMG3525R030-Q1 650-V automotive GaN FETs and evaluation modules are expected to be available in the first quarter of 2021.

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