The automobiles 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., semiconductor content accounts for $250 per vehicle; thus automotive is a key sector in the company's analog 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. (Milpitas, Calif.).
So as the number of components increases, space requirements are shrinking. Efficiency thus becomes more critical.
As a result, analog-device makers are tailoring parts–from LED drivers to switching regulators–to meet automotive OEMs' requirements. Those 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 Technology, TI, National Semiconductor Corp., Catalyst Semiconductor Inc. and others are flooding the market with analog chips that meet those specs while adhering to the auto environment's space limits.
Switching vs. linear
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 switcher behaves 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 minimizes EMI radiation.”
An automotive switching regulator needs to be specified to work over a wide input voltage range, of 3 V to 60 V. The 60-V rating gives a good margin for 14-V systems, which are usually clamped in the range of 36 to 40 V, Armstrong said.
Linear recently unveiled the H-Grade version of the LT3437 step-down switching regulator. The device operates from continuous inputs of 3.3 V to 60 V and withstands transients up to 80 V. Its 500-mA internal switch delivers up to 400 mA of continuous output current at voltages as low as 1.25 V. Burst-mode operation reduces no-load quiescent current to less than 100 µA, maximizing battery run-time 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 µA, a 200-kHz switching frequency, soft-start capability and saturating-switch design of 0.8-ohm 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 45 V.
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, 350-mA LEDs at up to 94 percent 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 350 mA from supplies as high as 24 V to provide better inductor control and eliminate the need for a dedicated heat sink. Built-in load dump protection allows transients of 40 V to be safely handled, optimizing 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 colors individually via a serial interface, such as in dashboard or climate control,” Gary said.
National Semiconductor also offers a family of high-brightness LED drivers. Its LM3402 touts up to 95 percent efficiency for driving up to 525 mA of current. The two versions of the LM3402 LED driver provide wide input voltage ranges of either 6 to 42 V or 6 to 75 V. 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 analog 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 34-V LM4562 practically eliminates distortion, with total harmonic distortion plus noise (THD+N) of 0.00003 percent.The 34-V and 44-V audio op amps offer the key specifications required for superior audio performance and signal conditioning, including noise density of 2.7 nV/square root Hz, a 1/f noise corner of 60 Hz, and a 600-ohm output drive.
To ensure that the most challenging loads are driven without compromise, National's op amps offer a slew rate of 20 V/µs and a 55-MHz gain bandwidth. The LME49860 is unity-gain stable over a supply range of +/– 2.5 to 22 V and provides output current capability of 26 mA.
Over that supply range, the amplifier maintains a common-mode rejection ratio and power supply rejection ratio of more than 120 dB, and a typical low input bias current of 10 nA. The LME49860 retains its high performance while driving capacitive loads as high as 100 pF, according to National.