APPLICATION NOTE 3394

Frequently Asked Questions (FAQs) for Automotive Electronics

How will the move from 12-V auto battery systems to 42V affect the design of automotive electronic circuits?
ICs operate from 1.5 to 3.5V, and they will operate from 1 V or less in the near future. The ideal engine-control unit (ECU) will be designed to be compatible to enable ECU manufacturers to make the transition where applicable. Devices that make this possible will be attractive to Tier 1 suppliers so they can target one module to both markets. As the module input voltage increases to 42V, this change in power-supply topology will require dc-dc converters to step down the high voltage followed by the post linear regulators to generate the multiple rails needed in the module (Fig. 1).


Will power budget design considerations change as the result of new 42-V auto batteries?
Yes. Despite lower supply voltage ICs that consume less power, more electronics are being used in cars. In fact, the number of ICs will increase substantially over the next five years. This increase is the main reason for OEMs looking to 42V to begin with, as alternator loads are already at their maximum capacity. Intelligent battery monitoring systems are being implemented for load-shedding and other power-saving features. Even simple components like a remote keyless entry (RKE) system for a keyfob or keychain must be designed for minimum power consumption, even though it derives its power from its own small battery (Fig. 2).


How will an auto's operating environment influence my designs?
Autos face very harsh environments, from the frozen tundras of Alaska to the searing hot deserts of Arizona, so ICs need to handle various temperature extremes, depending on the vehicle location. Under-the-hood modules must handle -40°C to 150°C ambient conditions, with the die operating temperature running even higher.

Electrical characteristics and performance specifications must be simulated, verified, and calibrated over this increased temperature range. ICs also must endure shock and vibration and acceleration/ deceleration effects. Therefore, ICs and subsystems must be designed to withstand these conditions, which include package design and testing, to last for the average automotive lifetimes of at least 10 to 15 years.

What effects do EMI/EMC play in automotive electronics designs?
Designing for electromagnetic interference/electromagnetic compatibility (EMI/EMC) will be a large factor. Numerous issues are involved. First, there is a huge number of high-current inductive loads with very noisy switching characteristics. These loads create transients across the electronic power systems that are coupled to the wiring harnesses by multiple paths. ICs must be robust to withstand these highvoltage events. Care must also be taken to limit the emissions by these loads. Second, switching dc-dc converters are becoming more common as well. So, ICs must be designed with stateof-the-art techniques and power topologies that help reduce EMI emissions. Not only is the number of dcdc converters increasing in cars' automotive electronic modules, the number of modules needed is increasing as well, and all of these modules are susceptible to the noise created. Third, increased automotive electronic content means more modules need to talk to each other over a growing network. Communications data rates are also increasing, challenging designers of ICs with fast communication data rates to minimize EMI emissions. Finally, low-voltage ICs are more susceptible to EMI due to a smaller noise margin, so the lengthy wiring bundles that interconnect them must be protected against EMI/EMC effects.

What software factors must be considered for automotive electronics designs?
Automotive electronics designs are using more software codes and microcontrollers, and this problem is expected to become worse. Software codes and algorithms written for microcontroller units (MCUs) must be more efficient. Efficiency and software reuse are prime drivers. Presently, some 40 to 60 MCUs are used in any given automobile. The number of lines of code written for automotive MCUs is projected to rise by 100 times, so there is an obvious need to tackle this growing problem. International automotive consortiums like AutoSAR have already been formed to come up with a standard software vehicle infrastructure by 2006 to deal with this problem. These consortiums hope to reduce the number of MCUs needed to about 20.

What is a TPMS, and what design criteria does it entail?
A tire-pressure monitoring system (TPMS) consists of an electronic module containing a sensor, signalconditioning electronics, a transceiver, and a power source (usually a small battery) located in the wheel hub of each of a car's tires. A dashboard-mounted readout informs the driver of each tire's pressure status. Four important design issues are involved here: low cost (projected to be about $5 to $6 per module for automotive manufacturers), battery lifetime, RFI/EMI, and operational reliability in a hostile environment of extreme temperatures, shocks, and vibrations.

How does Maxim help designers achieve high-voltage static protection for automotive circuit designs?
Maxim's MAX3000E/3001E/3002-3012 ESD-protected 20-Mbit/s optical logic translators offer ESD protection up to ±15 kV. They're packaged in a tiny UCSP package that saves space and replaces up to 10 discrete components and allow low-voltage ASICs with a supply voltage down to communicate with higher peripherals up to 5.5 V. They're pin protected by the Human Body Model, ensuring strict compliance with international standards.

What support will Maxim offer in low-cost optical transmission?
The MAX3901/3902 150-Mbit/s fiber-optic receivers (8-50 Mbits/s for the MAX3901) are optimized for low-cost polymer-clad silica (PCS) and plastic optical fiber (POF) automotive receivers. These parts operate over an extended temperature range (junction) of -40°C to 140°C, feature an input range of 1.2mA to 1mA, and operate from a 3.3-V or 5-V (MAX3901) supply voltage. Input sensitivity is 1.2mA p-p.

How will Maxim deal with "cold cranking" conditions that require certain electronic components like the engine-control unit (ECU) to retain their functional operation during the cranking phase?
To make sure that actual automobile cold-start performance functions properly without the need for reprogramming MCU settings in the ECU, you can use the MAX1523 and the MAX1634. The MAX1523 can be used as a low-input-voltage-enabled boost stage ahead of the MAX1634 main buck regulator.

Does Maxim support driver ICs for many different automotive display technologies?
Yes. One example is the MAX6920, a 12-output, 76-V, vacuum-fluorescent-display (VFD) tube driver. It interfaces a multiplexed VFD tube to a VFD controller, such as the MAX6850-MAX6853, or to a microcontroller. The MAX6920 is also ideal for driving either static VFD tube.

With many power ICs being used in automotive applications, is there a need for an accurate and flexible voltage reference?
Yes. One device Maxim makes is the MAX6037, which offers the lowest drift in the industry (25 ppm/°C maximum) over a temperature range of -40°C to 85°C and features 0.2% initial accuracy maximum. This 5-pin SOT device has an adjustable output-voltage reference range of 1.25V to 4.096 V. A shutdown mode reduces supply current to a mere 1mA maximum for power-sensitive systems.