ROHM’s gate driver IC with built-in isolator optimal for SiC MOSFET, IGBT and power MOSFET

1. Prevalence of power electronics

In recent years, attention is focused on power electronics mainly in the fields of industrial equipment, renewable energy and expanding widely in automotive-inverters. In the field of industrial equipment, factory automation and introduction of sophisticated robots have progressed, and markets of general-purpose inverters/UPS and servo amplifiers have been expanding year after year. New markets are expanding for power converters including solar-inverters and power-storage devices in the field of renewable energy and for EV/HEV in the automotive field.

In India, recent developments include design-upgrades to improve efficiency by utilizing high-frequency circuits for Solar-inverters, Hi-power UPS systems, Cellular base-station power supplies, Fuel-cell systems and Railway power converters, which demands need for Gate-drivers with isolators.

In accordance with generation of new application fields and markets, global power-demand has been increasing year after year, and energy-savings has become essential in equipment’s design. Therefore, high efficiency of inverter and converter circuits used in power electronics, especially for power supply and motor drives requiring high-power conversion, has become indispensable.

While high efficiency is required, challenges for downsizing have also increased. Downsizing is generally attained by high frequency operation that requires, besides sophistication of driving performance of gate driver, optimizing gate drive voltage for the SiC MOSFET, IGBT and power-MOSFET devices. However, effect of surges and influence of switching-noise has to be considered as voltage increases, safety-minded circuit design is necessary, when downsizing inverters and converters by simply increasing frequency.

In order to realize high efficiency and downsizing in such background, various demands have increased for high performance of power devices and gate drivers driving the devices.

Market expansion is expected in the future for SiC power devices, which are progressively adopted in next-generation inverters, as keystones for high efficiency. Adoption of SiC-diodes has already started implementing in PFC circuits of high-capacity power supplies and power-conditioners, and marketing of products using SiC MOSFET for switching applications is expected to increase gradually in the future. (Fig. 1)

　　　　　　　                     Fig. 1 Market trend of SiC power devices

*Source: ROHM compiled data based on Fuji Keizai Co., Ltd “Reality and Future Prospect of  Next Generation Power Device and Power Electronics Related Apparatus Market 2013”

While SiC MOSFET exhibits its maximum benefit of being able to make inverter highly efficient by high-speed switching, it has problems similar to those of conventional power devices such as countermeasures against the noise generated in gate drive circuit and safe design of protection circuits at the time of abnormality, such as short circuit.

2. ROHM’s gate driver IC with built-in isolator optimal for power electronics

Under these circumstances, gate driver circuits adopted with conventional photo-coupler system for power devices such as SiC and IGBT indispensable in sophistication in the field of medium/high voltage and high power applications. However, inferior high-temperature property and low speed of photo-coupler have been the problems of SiC circuits, whose advantage is in high-speed switching. As measures against such problems, ROHM developed gate drivers with built-in isolator that can maximally utilize performances of SiC, IGBT and power MOSFET by built-in isolators inside the ICs. In addition to ROHM’s “BM6104FV” having built-in short-circuit protection function, “BM60014FV” with simpler construction was recently developed to advance product development quickly, corresponding to various market needs.

ROHM’s gate drivers realized compact packages that are *industry’s smallest as ‘gate drivers with built-in isolator’, by combining its original Bi-CDMOS technology with newly developed ‘On-chip transformer’ technology. In “BM6104FV”, mounting-area was reduced by about 50% from conventional photo-coupler circuits by adoption of compact IC-package, which contributes to downsizing of inverter and converter circuits. Although circuit construction with many parts was necessary to realize similar functions in the past, number of parts is reduced by ‘built-in isolator IC’, and also contributes to improvement of inverter-circuit’s reliability as well as downsizing of drive substrates. (Fig. 2)

　　　Fig. 2 Internal construction and key features of ROHM’s gate driver with built-in isolator

Input/output delay-time was also reduced to less than about half from the first-generation products to enable realization of high speed. Drive capability is also increased, making high-speed of drive frequency and dead-time setting easy, and thereby enabling design of high efficiency drive circuit.

Further, power consumption can be significantly reduced compared with conventional photo-coupler system, and all the protection functions required for inverter circuits are built-in. For example, the gate driver itself judges abnormality when short-circuit occurs by means of the output short-circuit protection function, and stops switching action and activates ‘soft turn-OFF’ at the same time. This enables safe control of inverter action even during abnormality. Building in such fulfilling protection functions greatly contributes to downsizing of inverters as well as reduction of design load.

It also corresponds to high-speed switching of power MOSFET using SiC (Silicon Carbide) expected to be next-generation power semiconductor, and greatly contributes to realization of high-efficiency, low power-consumption in High-power Inverters and next-generation electric cars (EV).

3. Key features of products

3-1 Proprietary ‘On-chip coreless transformer’ technology utilized for 2,500 Vrms isolator (Fig.3)

　　Fig.3 ROHM’s original core-less transformer technology with integrated isolation function

3-2 Realization of compact package of industry’s smallest

The SSOP-B20W (Fig. 4) (6.5 mm x 8.1 mm, H=2.01 mm max.) package reduces mounting area by over 50% compared with conventional package types.

　　　　　　　　　　Fig. 4 Package size of Gate driver with built-in isolator

3-3 Multiple protection functions enable a high level of safety

All protection functions required for inverter circuits are built-in, including mirror-clamp function, fault-output function, under-voltage lock-out function, short-circuit protection function, and ‘soft turn-OFF’ function. Gate state monitoring function is also built-in. [BM6104FV]

3-4 High gate-drive capability

Correspondence to inverters with high frequency and wide capacity is possible with the high gate drive capability of 5A class (max.).

3-5 Input/output delay time

Input/output time is high, 150 ns. Delay-time was reduced to less than about half from conventional products. Minimum input/output pulse width of 90ns was also realized. Temperature characteristics are also excellent realizing stable operation in wide temperature range. (Fig. 5)

　　　　　　　Fig. 5 Input/output delay time, Turn-ON time, Turn-OFF time (Ta = 25°C)

3-6 Correspondence to wide operation temperature range

Operation temperature range is -40°C to 125°C, corresponding from low to high temperature environment. Small variation of delay time in wide temperature range makes it easy to examine drive circuit design. (Fig. 6) It can also correspond to automotive inverters in severe temperature environment.

Fig. 6 Comparison of input/output delay time of ROHM’s gate driver with built-in isolator with general photo-coupler system gate driver

　　　　　　　　　　Fig. 7 Line-up of Gate driver ICs with built-in isolator

4. Future efforts

In the future, in order to correspond to market needs of expanding industrial inverters and new energy converters, ROHM will take advantage of its strong analog-power technology to advance development of high-functional, high-reliability gate driver products that optimally drive power electronics including SiC and IGBT. ROHM also offers wide range of lineup in IGBT and SiC power devices (SiC-MOSFET, SiC-Diodes, SiC-modules) that meets the customer’s future needs.