From Isolation to the Third and a Half Generation: Understanding Naxinwei's Gate Driver IC in One Article

Whether it is MOSFET, IGBT, SiC MOSFET, or GaN HEMT, each power device requires a corresponding gate driver IC. A suitable driver IC can simplify the complexity of your system design and save R&D time. But an inappropriate driver IC may take you astray. So, how do you choose a suitable gate driver IC? We specially asked Pang Jiahua, the technical marketing manager of Nanochip Microelectronics, to interpret it. Pang Jiahua has been deeply involved in gate driver chips for many years and has extensive technical and industry experience.

Four indicators that cannot be ignored

Pang Jiahua, technical marketing manager of Naxin Micro, has been deeply involved in gate driver chips for many years. In his opinion, Naxin Micro's greatest advantage is that it maintains long-term communication with customers, has a lot of feedback experience, and is good at optimizing the driver design based on customer system applications. He believes that in actual selection, engineers and customers pay special attention to the four indicators of gate drivers.

First, the size of the driving current. For gate drive, the size of the driving current is the primary indicator of concern. It determines the driving capability of the gate drive. Combined with the external driving resistance, it comprehensively determines the switching time and switching loss of the power device tube, which directly affects the efficiency and EMI level of the system.

Second, the power supply withstand voltage value and the undervoltage point of undervoltage protection. For different power devices, the driving voltage is different, especially for third-generation semiconductors, the system noise and power supply fluctuations will be greater, and some systems will have very high overvoltage spikes. This requires the gate drive to have a higher voltage resistance to cover more application scenarios and reduce EOS risks. At the same time, for different power devices, the undervoltage point is also different. When the power supply is undervoltage, if the undervoltage point of the driver IC is too low, the power device cannot be shut down correctly, which will cause it to heat up and malfunction.

Third, anti-interference ability. CMTI is one of the important indicators to measure anti-interference ability. Especially for systems using third-generation semiconductor devices, the switching speed and bus voltage are both going up, which means that the dv/dt of the system is larger, and the gate drive needs a stronger anti-common mode interference ability, that is, a larger CMTI value.

Fourth, isolation or non-isolation, topology type. Isolation drive will pay more attention to the requirements of packaging, creepage and voltage resistance. Topology types include half-bridge topology and low-side topology. Half-bridge topology will pay attention to parameters such as whether the bootstrap diode is integrated internally, the upper and lower bridges are interlocked, or the dead time is adjustable.

Three types of gate driver chips

Judging from the above selection parameters, there are actually many ways to classify gate driver chips. Of course, there are also classification methods that better reflect the product characteristics. Naxinwei divides gate driver chips into three main categories.

The first category is isolation drive. At present, the market includes three mainstream isolation technologies: optical coupling isolation, magnetic coupling isolation and capacitive coupling isolation. All of Naxinwei's isolation drive products are developed based on capacitive coupling isolation technology. Naxinwei has been in this field for a long time and is the first manufacturer in China to launch isolation drive products. It also ranks first in the domestic market share and has been included in some international top Tier 1 and foreign models.

Isolation drivers have high reliability requirements and play a very important role in the system, so customer feedback is crucial. Naxinwei has a large shipment volume of isolation drivers, so it is able to collect a lot of customer feedback information. Naxinwei will make targeted optimizations based on the problems encountered by customers in the market. This is one of the advantages that competitors can hardly match.

Take the NSI6602x series of Naxin Micro, which has a large shipment volume, as an example. The input voltage range of this product is 3V~18V, the maximum supply voltage is 25V, there are four chips of 4/6/8/13V, support different UVLO levels, the drive current is up to 6A/8A, the CMTI is ±150kV/μs, and there are 6 types of packages to choose from. Compared with similar foreign products, its supply voltage input range is wider, the drive current is larger, the isolation withstand voltage level is higher, and there are more package types, which can cover more application scenarios.

The second category is non-isolated drive. Based on its experience in the field of isolated drive, Naxin Micro has gradually entered the field of non-isolated drive. In this field, Naxin Micro is more concerned about how to make distinctive products and overtake others. At the same time, it has made some general products for customers to use.

Take the high-reliability high-voltage half-bridge driver NSD1624 from Naxin Micro as an example. This product has an ultra-high withstand voltage of 1200V (SOP14)/700V (SOP8/LGA10), a drive current of +4A/-6A, a CMTI of about 100kV/μs, and an ultra-low propagation delay of 22ns (typ). Naxin Micro innovatively applies isolation technology solutions to the NSD1624 high-voltage half-bridge IC, which solves the above problems, namely: the pain points of SW pin negative voltage capability and high dv/dt.

The third category is the third-generation semiconductor driver. The reason why the third-generation semiconductor single gate is classified into one category is that the drivers required by SiC and GaN power devices are somewhat different from those of silicon-based power devices. Not only are higher requirements on the parameters of the driver or isolation itself, but the driver is also required to support more functions, such as protection functions under one-to-one sensitive working conditions.

Nanochip's silicon carbide driver has the advantages of both aspects, and it defines products together with customers; the gallium nitride driver is currently cooperating with some leading industry customers or some gallium nitride companies to design special products based on gallium nitride.

Take NSG65N15K, a packaged product launched by Naxinwei last year, as an example. It integrates a half-bridge driver and two E-mode GaN HEMTs with a withstand voltage of 650V and a resistance of 150mΩ, eliminating the common source inductance Lcs and minimizing the gate loop inductance Lg, thus avoiding the influence of stray inductance.

The core of six core technologies

The underlying technology supporting Nanochip's gate drive is composed of six core technologies: enhanced capacitor isolation technology, high common-mode anti-interference signal modulation technology (Adaptive OOK® encoding technology), isolation and Level Shift technology in high-voltage half-bridge, comprehensive protection functions (desaturation protection function DESAT, active Miller clamping function), ASIL D functional safety technology and GaN drive technology.

Among them, enhanced capacitor isolation technology and isolation and Level Shift technology in high-voltage half-bridge are basic IP technologies and belong to the basic requirements of driver chips. In particular, the enhanced capacitor isolation technology, which is the first in China to obtain a VDE certification report, uses bilateral isolation technology and is the earliest IP developed by Nanochip, which is used in all isolation products.

On top of the basic IP, the key is how to add functional safety, silicon carbide, gallium nitride and other new generation semiconductor material technical requirements. Therefore, protection functions, ASIL D functional safety technology, and GaN drive technology are the core technologies of Nanochip in the field of gate drive. In addition, Nanochip will also provide a functional safety manual to help customers design their systems to a high enough functional safety level to pass system-level functional safety certification.

The knowledge hidden in the coupling

From the above, it is not difficult to find that Nanochip has firmly chosen capacitive coupling, and there is a lot of knowledge hidden in it, which starts with isolation itself.

The three mainstream technologies of optical isolation, capacitive isolation, and magnetic isolation are determined by their characteristics in principle: the optical coupler transmits the LED light source to the phototransistor through dielectric insulating materials such as air, epoxy resin or molding compound; the capacitive coupler, as the name suggests, is a capacitor itself, which can naturally block DC signals, so capacitive isolation is based on AC signal transmission; magnetic coupling uses the transformer principle, and current pulses pass through a coil to form a very small local magnetic field, which isolates and transmits signals through magnetic field energy transfer.

Optocouplers have certain bottlenecks, so they are in the process of being gradually eliminated. For example, optocouplers are very sensitive to temperature, and it is difficult to achieve a junction temperature exceeding 100 degrees; the life of optocouplers is relatively short; it is difficult to increase the switching speed of optocouplers, the propagation delay is large, and the consistency is not good; CMTI optocouplers can generally only achieve 30kV/µs, while magnetic coupling and capacitive coupling can generally achieve more than 100 kV/µs. These bottlenecks will make it very difficult to apply it to third-generation semiconductors, and judging from the application trend, the third-generation semiconductors will definitely be vigorously promoted in the future.