Auto Electronics

Freescale turns up light switch

Freescale Semiconductor has introduced the third generation of its eXtreme Switch portfolio with four high-side power switches – the first devices in the portfolio tailored for automotive lighting applications. The switches can drive high-intensity discharge (HID) xenon, halogen and light-emitting diode (LED) light sources, and are said to allow automakers to improve lighting efficiency, extend bulb life, reduce bill of material costs, and provide greater power management flexibility compared with more conventional products.

The eXtreme Switch Gen III models are N-channel MOSFET switches with on-resistance ranging from 10 milliohms to 35 milliohms per channel. They can simultaneously control the high sides of up to four light sources. The devices’ ability to accommodate multiple types of light sources enables vehicle manufacturers to employ a single common body module design throughout its vehicle lineup.

The firm noted that today’s vehicles employ light sources ranging from halogen to xenon and LEDs. Each type has unique power requirements that vary during the different stages of its operation. According to Freescale, conventional switch solutions that employ electromechanical relays and fuses cannot provide system diagnostics and fault reporting.

The devices use performance profiles for each type of light source to precisely track its operation and deliver optimal efficiency and greatest protection. For example, a halogen lamp draws high levels of current when first turned on, but much less once it has stabilized. The ICs allow the lamps to draw high levels of current when needed at turn-on but less during operation. This technique makes it possible to accurately track the current drawn by the light source in the critical turn-on phase and quickly detect a potential overcurrent or short-circuit condition and turn off the lamp before failure occurs. This light source profile optimization allows automakers to reduce wire size (gauge), which can lower the overall weight and cost of the wiring harness.

For applications in which the light source is dimmed using a pulse width modulation (PWM) technique that varies the average power to the bulb to control the light intensity, the devices use a flexible PWM feature that tailors the PWM signal during load turn-on and turn-off, extending bulb life while providing full protection features.

The eXtreme Switch Gen III models provide diagnostics for the switch, light source and wiring harness, as well as fault management and control of the loads without complex software. The devices use latched overcurrent shutdown protection, which Freescale believes is preferable to the current limit method because it minimizes the thermal stress within the device during an over-load condition, reducing the junction temperature rise and vastly improving reliability.

Four protected high-side switches (at 25°C) are available with varying milliohms per channel. They are the MC15XS3400 (four 15-milliohm channels), MC35XS3400 (four 35-milliohm channels), MC10XS3412 (two 10- and two 12-milliohm channels), and the MC10XS3435 (two 10- and two 35-milliohm channels).

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