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EETE NOV 2013

AUTOMOTIVE ELECTrONICS Automotive infotainment system designs get easier with multi-output power management ICs By Steve Knoth and Jeff Marvin As product form factors are decreasing, demand for their functionality and features continue to increase. Furthermore, the industry trend for sophisticated digital ICs such as microprocessors and microcontrollers or field programmable gate arrays that power these products continues to lower their operating voltage while simultaneously increasing their amperage. Microprocessors are among the most popular of these to design in, and there is a growing list of power efficient types from such suppliers as Freescale, Intel, NVIDIA, Samsung, ARM and others. They are designed to provide low power consumption and high performance processing for a wide range of wireless, embedded and networking applications. The original intent of these processors was to enable OEMs to develop smaller and more cost-effective portable handheld devices with long battery life, while simultaneously offering enhanced computing performance to run feature-rich multimedia applications. Nevertheless, demand for this same combination of high power efficiency and processing performance has spread to non-portable applications. A couple of examples include automotive infotainment systems and other embedded applications, both of which demand similar levels of power efficiency and processing horsepower. In all cases, a highly specialized, high performance power management IC (PMIC) is necessary to properly control and monitor the microprocessor’s power so that all of the performance Fig. 1: LTC3676-1 simplified typical application diagram. benefits of these processors can be attained. Further, as the electronic content of automobiles continues to dramatically increase, so too has the use of microprocessors as the work horse of various control systems within the vehicle. Infotainment systems have captured a wide array of functions to enhance the driving experience. Touch screens, Bluetooth communication, digital and high-definition television (HDTV), satellite radio, CD/ DVD/MP3 players, global positioning system (GPS) navigation and video game systems have created a full-fledged entertainment center inside the car. Automotive PMIC challenges Electronic systems designed for automotive applications are challenging for many reasons, including the wide operating temperature range, strict EMC and transient requirements, as well as the high quality levels demanded by automotive OEMs. Starting with the wide operating temperature range, power management ICs are challenged on two fronts. First, power conversion - even when highly efficient - must dissipate some level of power as heat. When several DC-DCs and LDO regulators are packed into a single device, the combined power dissipation can be significant, easily approaching two Watts or more. Typical PMIC packages such as the 6x6mm 40-pin, exposed pad QFN have a thermal resistance of 33°C/W resulting in a junction temperature rise in excess of 60°C. When this is combined with the additional challenge of a wide ambient operating temperature range, the maximum junction temperature of the PMIC can often exceed 125°C. Even in body electronics, not under the hood, the ambient temperature inside a sealed plastic electronic control module can reach 95°C. Due to these temperature challenges many PMICs rated for 85°C, or even 125°C, are not sufficient for sustained high temperature operation. Another key to operating an integrated power management device in a high ambient temperature environment is for the device to self-monitor its own die temperature and report when its junction temperature is getting too high so that the system controller can make an intelligent decision on whether to reduce power to the load(s). Operating system software can do this by turning off less critical functions or by turning down the performance in processors and other high power functions such as displays and network communications. The environment within a current vehicle’s dashboard is crowded with electronics. Adding to this crowding are radios from Bluetooth to cell phone based network connectivity. Therefore, it is imperative that any additional entries to this thermally constrained environment not contribute excessive heat or EMI. There are strict Electromagnetic Compatibility (EMC) requirements which cover radiated and conducted emissions, radiated and conducted immunity or susceptibility, and Electrostatic Discharge (ESD). Being able to conform to these requirements affects the performance aspects of a PMIC design. Some are straightforward, such as the DC-DC switching regulators must operate at a fixed frequency well outside of the AM radio band. However, another common radiated emission source found in DC-DC converters comes from the switching edge rates of its internal power MOSFETs. These edge rates should be controlled to reduce radiated emissions. Many of today’s embedded systems and advanced processors require controlled and choreographed sequencing as power supplies are powered up and applied to various circuits. Allowing for system flexibility and a simple approach to sequencing not only makes the system design easier, but it also enhances system reliability and allows for a single PMIC to handle a broader range of the system than just a specific processor’s requirements. In summary, the main challenges facing the automotive infotainment system designer include balancing power dissipation with the high level of integration of multiple switching regulators and linear regulators, accurately regulating output voltage and load step response required by advanced nanometer technology processors and FPGAs. Steve Knoth is Senior Product Marketing Engineer at Linear Technology – www.linear.com Jeff Marvin is Design Center Manager for the Power Products Group at Linear Technology. 24 Electronic Engineering Times Europe November 2013 www.electronics-eetimes.com


EETE NOV 2013
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