System-level power ICs blend brains with brawn

Electronic News, August 18, 1997 by Virginia Natale

With little fanfare, smart power integrated circuit technology has evolved to where entire systems can be carved onto a single substrate which combines analog and linear bipolar, digital CMOS, and power DMOS circuits. The result is a system-oriented mixed technology that replaces multiple chips with one, and opens new applications to the advantages of compact electronic control.

With system-oriented technology, electronic controls can now be added where, for reasons of space, none were previously practical. Moreover, by replacing existing board-level designs, the same technology yields more reliable and less costly power controls. In either case, the benefits of such super-smart, system-level power ICs are already rippling through automotive, industrial, consumer and other fields.

One example of a chip-level system is a smart battery charger circuit that includes a dc-dc converter, an A/D converter, microcomputer core, and EPROM program storage. Another is a door lock actuator, which integrates a microcontroller, power stage, and bus interface among other circuits. In both cases, an important advantage of system-oriented technology is reduced circuit size. In the case of the smart battery charger, small circuit size is especially crucial. If the smart charger chip was too large, any operating time gained by intelligent power management would be offset by the loss of battery volume.

Although different circuit technologies have been blended in the past to produce smart power chips, system-oriented technology integrates much larger portions of the overall system. Because of that, the technology plays a greater role in determining how system functions are partitioned. Moreover, integrating a microcontroller on a power circuit adds several important benefits.

For one, the design is more flexible, allowing functions to be changed by simply modifying the software--this is a much faster and less expensive path than redesigning the chip. Also, using nonvolatile memory makes it possible to program a finished chip during production of the end equipment. This option makes it easy to manufacture different models on the same production line. It also ensures that equipment leaves the manufacturing floor with the latest software.

BCD III Technology

Among the system-oriented technologies available today for high-volume production is BCD III technology. This third-generation technology combines bipolar, CMOS, and DMOS circuits--hence the name BCD--having feature sizes as small as 1.2 microns. In addition, the next-generation technology, BCD5, is presently under development and promises feature sizes of 0.6-micron. It will include EEPROM and be compatible with flash memory processes.

For switching power, BCD III allows the integration of both vertical and lateral DMOS devices. Vertical devices operate at up to 60V or 80V and have "on" resistances of 0.25 and 0.3 ohms/square mm, respectively. Lateral DMOS devices can handle 16V, 20V, or 40V and have respective on resistances of 0.08, 0.13, and 0.17 ohms/square mm.

In addition, the process allows two types of NPN transistors: one with a 30V Vceo, the other with a 16V Vceo and 1GHzf. Other structures that can be integrated with the BCD III process include 5V and 12V CMOS components; low- and high-voltage lateral PNP transistors; high-voltage MOS transistors; low leakage diodes; EPROM and EEPROM; 5V buried Zener diodes; 5V, 20V, and 60V dielectric capacitors; and both diffused and high-ohmic polysilicon resistors.

A newly developed one-chip hydraulic servo-valve controller illustrates how BCD III technology makes electronic controls more practical and affordable. Using the 60V-DMOS version of BCD III, designers integrated a board-level servo-valve controller into a 64-pin chip containing a central processing unit, EPROM, UART, 256-byte RAM, 16-bit PWM timer, watchdog supervisor, 5V regulator, 8-bit A/D converter, and a power H-bridge capable of handling up to 4A.

The chip controls the position of a spool within a servo valve, which in turn adjusts the hydraulic pressure to an actuator. For accuracy, a sensor feeds the position of the spool back to the controller chip, where that information is compared to the command signal.

Hydraulics: A Practical Example

Applications for this type of control include active suspension, power steering, and servo-braking systems, as well as a wide range of functions in industrial, agricultural, aerospace, and military sectors. In fact, wherever hydraulic equipment is used, including cranes, winches, fork lift trucks, hydraulic presses, and aircraft. Electronic control affords precise acceleration, velocity, positioning, and flow, which all contribute to greater reliability and improved performance of the hydraulic system. It also allows an operator to control machinery from a safe, convenient distance. Also, the on-chip EPROM lets individual controllers be calibrated to achieve the desired performance and accuracy.

Most significant for many of these applications, where space is limited and light weight is important, BCD technology's ability to replace an electronic controller board with a chip not only reduces the cost of the electronics, it also shrinks the electronics enough to actually fit within the motor that drives the servo-valve.