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Analogue device makers address car OEMs' needs

Posted: 16 Oct 2007     Print Version  Bookmark and Share

Keywords:in-vehicle processing power  analog chips  automotive electronics  switching regulators  linear regulators 

The cars that consumers will be driving 10 years from now will differ vastly from those on the road today. The key difference will be the use of electronics to make vehicles safer, more energy-efficient and more fun to drive.

In-vehicle processing power will continue to increase in tandem with advances in electronics, fueling demand for components. According to Texas Instruments Inc., IC content accounts for Rs.10,112.07 ($250) per vehicle; thus, automotive is a key sector in the company's analogue chip sales strategy.

But the automotive environment is a harsh one for electronics. Wide operating voltage requirements, high transient voltages and wide temperature excursions are tough on electronics systems, said Tony Armstrong, product marketing manager for the power product group at Linear Technology Corp.

So as the number of components increases, space requirements are shrinking. Efficiency thus becomes more critical.

As a result, analogue device makers are tailoring parts to meet automotive OEMs' requirements, which include a wide input voltage operating range; good efficiency over a wide load range; low quiescent current during normal operation, standby and shutdown; low thermal resistance; minimal noise and EMI emissions; and a wide operating temperature range.

Linear, TI, National Semiconductor Corp., Catalyst Semiconductor Inc. and others are flooding the market with analogue chips that meet those specs while adhering to the auto environment's space limits.

At low output voltages and moderate current levels, Armstrong said, it is impractical to use a linear regulator to drive system voltages. Thermal constraints have switching regulators replacing linear regulators, he said.

"Although switching regulators generate more noise than linear regulators, their efficiency is far superior," Armstrong said. "Noise and EMI levels have proved manageable in many sensitive applications as long as the switches behave predictably. If a switching regulator switches at a constant frequency in normal mode, and the switching edges are clean and predictable with no overshoot, frequency can provide a small, tight layout, which minimises EMI radiation."

An automotive switching regulator needs to be specified to work over a wide input voltage range of 3V to 60V. The 60V rating gives a good margin for 14V systems, which are usually clamped in the range of 36-40V, Armstrong said.

H-Grade version
Linear recently unveiled the H-Grade version of the LT3437 step-down switching regulator. The device operates from continuous inputs of 3.3V to 60V and withstands transients of up to 80V. Its 500mA internal switch delivers up to 400mA of continuous output current at voltages as low as 1.25V. Burst-mode operation reduces no-load quiescent current to less than 100?A, maximising battery runtime for always-on applications.

The H-Grade version performs at a junction temperature of 140?C, vs. the E- and I-Grade versions' 125?C maximum junction temperature. Other features include shutdown current of <1?A, a 200kHz switching frequency, soft-start capability and saturating-switch design of 0.8Ω on-resistance.

On the switch-mode regulator side, TI is offering the TPIC74100-Q1, with a buck/boost feature that lets the user extend the input voltage range even below the output voltage of the device. That feature ensures full operation during a cold-crank operation, such as starting the engine. Other features include low standby current, high efficiency and an input-voltage capability of up to 45V.

Linear voltage regulators are also part of TI's lineup of automotive parts. Its TLE4275-Q1 offers low quiescent current, helping customers conserve battery energy in applications that are powered even when the car is not in operation.

For driving high-brightness LEDs in step-down applications, Catalyst Semiconductor developed a buck converter that offers a simpler and smaller alternative to linear regulators. Housed in a T-SOT-23 package, the CAT4201 drives high-brightness, 350mA LEDs at up to 94 per cent efficiency.

The CAT4201 incorporates Catalyst's switching control algorithm, which is said to reduce system complexity and improve efficiency. It lets an external RSET control resistor preset a regulated LED current up to 350mA from supplies as high as 24V to provide better inductor control and eliminate the need for a dedicated heat sink. Built-in load dump protection allows transients of 40V to be safely handled, optimising the CAT4201 for automotive indicator and illumination lighting applications, including turn-signal, brake and map-reading lights.

Incandescent light bulbs are being replaced by LEDs for their intensity, reliability and design flexibility, said Mark Gary, marketing manager for mixed-signal automotive products at TI, which provides solutions for applications ranging from power train to braking to audio infotainment.

"Depending on the application that the LEDs are used in, solutions range from supplying constant current with high efficiency, independent of battery voltage variations--such as in screen backlighting in infotainment applications--to controlling multiple LEDs with different colours individually via a serial interface, such as in dashboard or climate control," Gary said.

TI's key parts in LED lighting include the TPS61042 low-power DC/DC boost converter and the TLC59xx series of 8bit and 16bit constant-current LED drivers.

National Semiconductor also offers a family of high-brightness LED drivers. Its LM3402 touts up to 95 per cent efficiency for driving up to 525mA of current. The two versions of the LM3402 LED driver provide wide input voltage ranges of either 6-42V or 6-75V. Its hysteretic control with controlled on-time, coupled with an external resistor, allows the converter output voltage to adjust as needed to deliver a constant current to series- and series/parallel-connected arrays of LEDs of varying number and type.

The analogue chip maker also serves the auto market with its LM4562/LME49860 high-fidelity audio op amps, which serve as line driver/receivers, active filters, buffers or preamplifiers.

The 34V LM4562 practically eliminates distortion, with total harmonic distortion plus noise (THD+N) of 0.00003 percent. The 34V and 44V audio op amps offer the key specifications required for superior audio performance and signal conditioning, including noise density of 2.7nV/√Hz, a 1/f noise corner of 60Hz, and a 600Ω output drive.

To ensure that the most challenging loads are driven without compromise, National's op amps offer a slew rate of 20V/?s and a 55MHz gain bandwidth. The LME49860 is unity-gain stable over a supply range of ?2.5-22V and provides output current capability of 26mA.

- Ismini Scouras

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