Naxin Micro provides full-scenario GaN driver IC solutions-EEWORLD

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As a popular third-generation semiconductor technology, GaN has a wide range of applications in data centers , photovoltaics, energy storage, electric vehicles and other markets. Compared with traditional Si devices, GaN has higher switching frequencies and lower switching losses , but it also places higher requirements on driver IC and driver circuit design.

According to the differences in gate characteristics, GaN is divided into two types: normally open depletion mode (D-mode) and normally closed enhancement mode (E-mode); according to the differences in application scenarios, GaN requires multiple driving modes such as isolation or non-isolation, low-side or bootstrap, zero volt or negative voltage shutdown. For different types of GaN and various application scenarios, Naxinwei has launched a series of driver IC solutions to help give full play to the performance advantages of GaN devices.

01 Depletion-mode (D-mode) GaN drive solution

1. D-mode GaN Types and Characteristics

Since the normally-on depletion-mode GaN itself cannot be used directly, it is necessary to add peripheral components to change the D-mode GaN from normally-on to normally-off, mainly including cascode and direct drive technology architectures; among them, the cascode D-mode GaN is more mainstream. As shown in Figure 1 below, the cascode D-mode GaN uses the switch of the low-voltage Si MOSFET to drive the overall switch, thereby changing the normally-on type to the normally-off type.

Figure 1 Structure of cascade-type D-mode GaN

Although low-voltage Si MOS has an additional channel resistance when turned on and participates in the overall switching process of the device, the overall impact on the GaN device is very limited because the on-resistance and switching performance of low-voltage Si MOS are ideal in themselves.

The biggest advantage of cascade-type D-mode GaN is that it can be controlled at 0V/12V level using the traditional Si MOS drive circuit . However, it should be noted that although the drive circuit is the same as Si MOS, the switching frequency and speed of the cascade-type D-mode GaN are much higher than those of traditional Si MOS, so the driver IC is required to work normally in a very high dv/dt environment.

As shown in Figures 2 and 3 below, the typical application circuit of GaN using a half-bridge topology, the high-frequency, high-speed switching of GaN will cause a high dv/dt jump in the potential of the midpoint of the half-bridge. For non- isolated driver ICs, the internal level shifter parasitic capacitance of the driver chip will generate common-mode current under high dv/dt ; for isolated driver ICs, the input and output coupling capacitors of the driver chip also constitute a common-mode current path. These common-mode currents coupled to the signal input side will interfere with the input signal, which may trigger the driver chip's malfunction, and in severe cases may even cause GaN to have a bridge arm direct pass.

Figure 2 Common-mode interference propagation path of non-isolated half-bridge driver IC

Figure 3 Common-mode interference propagation path of isolated half-bridge driver IC

Therefore, common mode transient immunity (CMTI) is an important indicator for selecting GaN driver ICs. For GaN devices, especially for high voltage and high power applications, it is recommended to use driver ICs with a CMTI of more than 100V/ns to meet the needs of higher switching frequencies and faster switching speeds.

2. Nanochip D-mode GaN drive solution

Naxinwei provides a variety of driving solutions for D-mode GaN to meet the needs of different application scenarios such as different power ranges, isolation or non-isolation.

1) NSD1624: High reliability high voltage half bridge Gate driver

Traditional non-isolated high-voltage half-bridge driver ICs generally use a level-shifter architecture. Due to the limitation of internal parasitic capacitance, they can usually only withstand common-mode transients of 50V/ns. NSD1624 innovatively applies isolation technology to the high-side drive of high-voltage half-bridge driver ICs, increasing the dv/dt tolerance to 150V/ns, and the high-voltage output side can withstand up to ±1200V DC voltage. In addition, NSD1624 has a +4/-6A drive current capability and can operate in a 10~20V voltage range. Both the high-side and low-side outputs have independent power supply undervoltage protection (UVLO). NSD1624 is available in SOP14, SOP8, and small LGA 4*4mm packages , which are very suitable for high-density power applications and can be applied to various high-voltage half-bridge and full-bridge power topologies.

Figure 4 NSD1624 chip functional block diagram

2) NSI6602V/NSI6602N: Second generation high performance isolated dual channel gate driver

NSI6602V/NSI6602N is the second generation of high-performance isolated dual-channel gate drivers from Naxin Micro. Compared with the first generation, it further enhances the anti-interference and driving capabilities, improves the voltage resistance on the input side, and has lower power consumption, and can support a maximum operating switching frequency of 2MHz. Each channel output provides a maximum 6A/8A source current capability with a fast 25ns propagation delay and a maximum delay matching of 5ns. The 150V/ns common mode transient immunity (CMTI) improves the system's ability to resist common mode interference. NSI6602V/NSI6602N has multiple packages to choose from, and the smallest package is a 4*4mm LGA package, which can be used in scenarios with high power density requirements such as GaN.

Figure 5.1 NSI6602N chip functional block diagram

Figure 5.2 NSI6602V chip functional block diagram

3) NSI6601/NSI6601M: Isolated single-channel gate driver

NSI6601/6601M is an isolated single-channel gate driver that provides split outputs for controlling rise and fall times separately. The input side of the driver is powered by a 3.1V to 17V power supply voltage, the maximum output side power supply voltage is 32V, and both the input and output power pins support undervoltage lockout (UVLO) protection. It can provide 5A/5A source/sink peak current, and the minimum common mode transient immunity (CMTI) of 150V/ns ensures system robustness . In addition, NSI6601M also integrates Miller clamping function, which can effectively suppress the risk of misleading turn-on caused by Miller current.

Figure 6.1 NSI6601 chip functional block diagram

Figure 6.2 NSI6601M chip functional block diagram

02 Enhanced (E-mode) GaN drive solution

1. E-mode GaN Types and Characteristics

Different from cascode D-mode GaN which realizes normally-off mode by cascading low-voltage Si MOS, E-mode GaN directly dopes the GaN gate with p-type to modify the band structure and change the gate's on-threshold, thereby realizing a normally-off device.

According to the different gate structures, E-mode GaN is divided into two technical routes: current type with ohmic contact and voltage type with Schottky contact . Among them, voltage type E-mode GaN is the most mainstream. The following will mainly introduce the driving characteristics and solutions of this type of GaN.

Figure 7 Voltage-mode E-mode GaN structure

The advantage of this type of E-mode GaN is that it can achieve 0V shutdown and positive voltage conduction without damaging the conduction and switching characteristics of GaN. Since GaN has no body diode , there is no reverse recovery problem of the diode, which can effectively reduce switching losses and EMI noise in hard switching situations. However, the voltage-type E-mode GaN driving voltage range is narrow, and the typical driving voltage range is generally 5~6V, and the turn-on threshold is also very low. It is sensitive to interference and noise in the driving circuit. Improper design can easily cause GaN to turn on incorrectly or even gate breakdown.

Table 1 Comparison of driving voltage between E-mode GaN and Si Mos

*The negative voltage tolerance of E-mode GaN gates from different brands varies greatly, some can only tolerate -1.4V, while others can tolerate -10V negative voltage.

In low voltage, low power, or applications that are sensitive to dead zone losses, 0V voltage shutdown can generally be used; however, in high voltage, high power systems, negative voltage shutdown is often recommended to enhance noise immunity and ensure reliable shutdown. When designing the negative voltage for gate shutdown, in addition to considering the gate voltage resistance of GaN itself, the impact on efficiency must also be considered. As shown in the table below, this is because E-mode GaN can achieve reverse current flow, i.e., third quadrant conduction, in the off state, but the reverse conduction voltage drop is related to the negative voltage value of the gate shutdown. The more negative the voltage used for gate shutdown, the greater the reverse voltage drop, which will correspondingly bring greater dead zone losses. Generally, for high voltage applications above 500W, especially hard switches, a shutdown negative voltage of -2V~-3V is recommended.