High-voltage ICs improve performance by design

High-voltage ICs improve performance by design

Next-gen analog ICs provide high-power features that can manage and survive catastrophic events

BY HENNING HAUENSTEIN
International Rectifier, El Segundo, CA
http://www.irf.com

Analog IC processes have followed a path of higher integration and increasing complexity, although not to the same degree as digital ICs. Nevertheless, the analog world, too, has reached some very small structure sizes. This allows the implementation of enough logic functionality to provide very smart analog ICs with enormous capabilities.

Previous-generation devices with relatively simple general-purpose drivers have evolved into fully protected application-specific driver ICs with safety functions that can manage and survive extreme events such as shutting down a motor in a failure event without the need of the microcontroller. Application-specific protection features, temperature, current and voltage sensing are standard functionalities that can be processed by the analog IC independently from a microcontroller. In addition, to reduce component count and make the design easier and more reliable, the new generation of ICs feature integrated bootstrap functionality implemented by means of an internal high-voltage MOSFET whose biasing conditions are effectively managed to deliver current to the high-side circuit through the low-side supply network, emulating the external high-voltage bootstrap diode.

These latest-generation ICs (see Fig. 1 ) can make critical decisions on required actions needed for the power management independent from the outside world. In extreme situations these capabilities allow system designers using these ICs to rely in many cases fully on the analog IC alone which often saves critical milliseconds to prevent the system from catastrophic failures.

Fig. 1. IRS26310D High-voltage 3-phase gate driver IC functional block diagram.

The future for analog ICs

In the near future, more power-hungry applications will evolve, among other factors driven and enabled by the availability of more-powerful switches such as trench MOSFET and IGBTs with a never-before-seen current density. This imposes tremendous challenges for the analog ICs that have to drive these switches reliably and safely. Only the strongest meaning the most fail-proof and noise/stress-immune ICs will be able to cope with the challenges of modern power management. The latest generation of analog ICs are fully optimized, tested, and characterized to withstand even catastrophic stress such as short-circuit events and are immune to their typical “natural enemies” such as transient negative voltage spikes in typical switching applications (see Fig. 2 ). This is a major milestone for analog power management ICs.

Fig. 2. Tolerant to negative transient voltage

Emerging applications for analog ICs include automotive, encompassing motor drive applications for hybrid electric vehicles (main power train, peripheral motors like air-conditioning) and dc/dc conversion. The stricter environmental laws and fuel-saving efforts will not only drive hybrid vehicle technology but also leverage a significant growth of direct fuel injection for diesel and gasoline engines with great opportunities for rugged analog driver ICs driving the actuators of modern fuel injectors.

In appliances, stricter laws require more protection and safety features for typical household appliances such as washers and dryers. Therefore, analog ICs with implemented protection features and reliable fail proof designs will gain more and more importance in these markets.

Industrial and consumer motor control, on one hand, will see an increasing number of power tools requiring efficient and rugged power management in the smallest space and lowest power consumption, while on the other hand, higher-power motor-drive applications in the field of construction equipment, golf carts, electric bikes will emerge as key markets.

Programmability versus ruggedness

Programmability for analog ICs is not necessarily the best solution for all applications. Combining programmability with typical analog capabilities will offer advantages in applications which require the highest integration and extremely compact designs in the smallest space. Next-generation HVIC technology will have the capabilities to address this demand, which will likely still be a niche for the near term.

However, the cost increase of these more-expensive “programmable technologies” and often the reduced ruggedness of such devices will probably not be the preferred solution for safety-critical applications or harsh environments. In addition, the higher complexity will increase the initial development cost of such an IC, which might make them too expensive for niche applications. Therefore, applications requiring programmable analog ICs will probably need to have enough volume to justify the development cost. So programmability of the analog IC could be a second step after an application is mature and a shrinking of the system components suggests monolithic integration of various components.

It is anticipated that standard analog IC technology will stay as the mainstream for many applications in the near future. Cost and performance optimized system architectures can often be achieved by using a chipset solution that uses devices produced with different silicon processes specializing in the various requirements for each component. In addition, the flexibility achieved by combining different ICs is often a very important factor for the system designer, especially in fast-changing markets with short product lifetimes.

Integrated design platforms such as iMotion provide complete motor drive solutions in the form of chipset solutions with digital capabilities, programmability, analog driver capabilities plus optimized switches such as IGBTs and MOSFETs (see Fig. 3 ). Each device uses different silicon processes optimized for each specific task rather than making tradeoffs by using a too highly integrated or complex process. Instead of having very complex system on a chip, the combination of ICs in a so-called system in a package (also called multichip packages) is a very competitive alternative to programmable monolithic solutions.

Fig. 3. iMOTION integrated design platform

In the field of very high power, there is more increasing demand for rugged and robust analog ICs. Programmability is not necessarily a feature that makes an IC more rugged, so it is more beneficial to focus on developing very rugged and robust analog ICs for higher power management tasks. High-temperature capabilities, robustness against transient voltage spikes, and fail-proof safety and protection features are probably the successful path for analog ICs in the higher power management arena.

Standardizing analog IC technology

Analog HVIC technology is based on the requirements of the power management applications in various markets such as automotive, industrial, appliances, audio, and lighting in a voltage range from 100 to 1,200 V. Standardization could be a topic on a product level for more mature applications while probably not the HVIC technology platform itself.

However, on the other hand the low-power BCD-world (typical voltage

Next-generation analog ICs provide fully protected application-specific features with safety functions that can manage and survive catastrophic events without the need for a microcontroller.

It is anticipated that standard analog IC technology will stay as the mainstream for many high power management applications in the near future, especially as part of integrated design platforms in the form of optimized chipset solutions with digital capabilities, programmability, analog driver capabilities plus optimized switches such as IGBTs and MOSFETs. ■