The Silicon Power Switch

At some point in the last two years, you may have found yourself driving behind a new Cadillac equipped with neon brake lights, or a truck or bus using the newer LED lighting. Did you notice the difference when those lights come on, that they seem to snap crisply into illumination and off again, as opposed to the incandescent lamps of neighboring vehicles?

Such is the fundamental difference between manual switching devices and solid-state switching ICs, which have been in existence for some time (and of which the transistor is the evolutionary starting point). Besides “clean” switching, a silicon device is not as susceptible to wear, contact malfunctions or corrosion over time.

Late last year, Motorola brought to market a 2 mW high-side power switch for systems that require up to 2 kW of power control. Designed for harsh environments, the MC33982 is a mixed-signal, multi-chip integrated circuit designed to replace electromechanical relays, fuses and discrete devices in a variety of embedded systems in appliances, power hand tools, dish positioning systems, and marine and automotive systems. The device combines high-density, high-speed logic with precision analog and high-voltage, high-current power circuitry. According to Bob Jarrett, vice president and general manager of Motorola’s Analog Products Division, “This device enables significant power savings and less heat generation in a number of applications.”

Operating voltage is 6.0V to 27.0V, with standby currents under 5.0 µA. Built-in protection, logic level control, and various configuration and communication features in the MC33982 switch help to simplify embedded system design efforts, lower system costs and increase system reliability. Used as a simple, logic level input controlled, high side FET, these features include: over-current and over-temperature protection; real-time fault status indication; ground disconnect and load dump transient protection; open load detection; and negative battery, over- and under-voltage protection. Additional abilities, accessible through a built-in serial peripheral interface (SPI), include: output on/off control; configurable over-current detection levels and blanking times for fuse emulation; selectable output slew rate control; device input status feedback; specific fault information and device status reporting; daisy chain capabilities; and a configurable turn-on delay for load demand optimization. Through the SPI, users can select and configure current sensing for real-time monitoring and a watchdog function with failsafe operation. The IC also has enhanced 16V reverse polarity V_PWR protection.

Packaged in a 12 x 12 mm power quad flat pack, the device’s thermal control is aided by its exposed heat sink. A dedicated parallel input is available for alternate and PWM (pulse width modulation) control of the output.

—RM