Robust Power Conversion, a Must Have for Truck, Automotive & Heavy Equipment

September 02, 2015 // By Bruce Haug, Linear Technology
Truck, automotive and heavy equipment environments are very demanding for any type of power conversion devices. Wide operating voltage ranges coupled with large transients and wide temperature excursions combine to make reliable electronic system design challenging. To complicate design considerations, some applications require the power conversion device be installed under the hood, requiring a high temperature rating. At the same time, as the number of electronic components is increasing, space requirements are continuing to shrink, making high efficiency conversion critical due to space limitations.

Consequently, reliable truck switching DC/DC regulators need to work over a wide input voltage range. A 60V input rating gives good margin for a nominal 12V system, which is usually clamped in the 36V to 40V range. Double battery applications, commonly found in both trucks and heavy equipment environments require an even higher operating voltage due to their nominal 24V battery voltage. Most of these are clamped to 58V, so a 60V rating is usually sufficient. The onboard automotive and truck overvoltage clamp is required to maintain a maximum transient voltage caused by the inductive kick back voltage from the starter motor, which can cause a much higher transient voltage when left unclamped.

There are several electronic systems that require continuous power even when the vehicle’s motor is not running, such as remote keyless entry, GPS and security systems. It is essential for these types of “always-on” systems to have a DC/DC converter with low quiescent current in order to maximize the battery run time when in sleep mode. Under such circumstances, the regulator runs in normal continuous switching mode until the output current drops below a predetermined threshold of around 30-50mA. Below this level, the switching regulator must go into lower quiescent current operation in order to reduce the current draw to tens of micro amps, thereby lowering the power drawn from the battery which in turn extends the battery run time.

With 60V input capable DC/DC converters that have high step-down ratios in short supply, designers have resorted to a transformer-based topology or external high side drivers to operate up to 60V. Others have used an intermediate bus converter, requiring an additional power stage. Both of these alternatives increase the design complexity and, in most cases, reduce the overall efficiency. However, the LTC3892 from Linear Technology, is the latest part in a growing family of 60V input capable step-down switching regulator controllers that addresses many of the key

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