At last month’s electronica 2012, the mega tech-fest held in Munich, three companies launched new products that specifically target the vehicle interior ambient-lighting space. Controlling the colour of an RGB LED module via a LIN network means that it’s possible to produce almost any colour of interior lighting. Furthermore, such technology allows users to control the colours. But do consumers really want this capability?
“Earlier versions of RGB have been introduced in several models of cars, and it turns out that this option has a high take-rate,” says Wim Van de Maele, ASSP marketing manager at ON Semiconductor. Van de Maele points out that the interior of the car is regarded as being more important to the owner than the exterior, and user-controllable lighting colours can be adapted to regional tastes to appeal to all drivers.
“Depending on the MMI [man-machine interface] software that is used, OEMs can give full flexibility to the user to control the colour, or keep the choice to only some selected values,” he adds.
You can forget about in-car disco lighting, though. The controllable interior lighting will likely be limited to subtle changes.
For instance, different colour settings can affect the driver’s mood. Studies are being performed to pinpoint optimum settings, perhaps for maximum contrast between the car’s interior and the outside world when driving in darkness. Van de Maele also suggested that a reddish colour could give a warmer feeling in winter, and a bluer colour providing a cooler feeling during summer.
Targeting this market, ON Semiconductor developed the NCV7430, a LIN-based, single-chip multicolour LED driver (Fig. 1). Three independent current regulators supply up to 30 mA to each LED channel; customised extensions for current boosting can push it to 1 A. Other extensions could incorporate temperature compensation, dissipation balancing, or auto-addressing using a LIN switch method.
The NCV7430, packaged in 8.75mm-by-6.2mm SOIC14, is typically assembled on a small PCB alongside an RGB LED chip. Boards can be calibrated to compensate for the processing spread of the LEDs.
Reduced Wiring
Another product launch at electronica was Atmel’s latest LED driver. Claus Mochel, Atmel’s marketing manager for Automotive Products, explained that in addition to aesthetic considerations, interior lighting can help to clearly highlight storage areas or control elements, such as the roof module, to make them more visible when driving at night.
Mochel also explained the benefits of using LIN in this application: “The main benefit is that only one [LIN bus] wire is needed to indicate to each module which lighting settings are to be applied. This reduces the application cost and enables the automotive designers to develop more complex timing sequences of the lighting application. When using the LIN bus’ auto-addressing option, it is possible to cover all kinds of lighting functionalities within a car with just one module.” Shorter wiring also has positive implications for EMC.
Atmel’s ATA664151 and ATA664251 (Fig. 2) each have three current sources that can drive up to 20 mA, controlled by independent PWM signals.
The ATA664151 contains a LIN 2.2- and SAEJ2602-2-compliant transceiver, based on Atmel’s third-generation LIN transceiver IP. It also features a low-drop 5V voltage regulator with 80mA current capability (the ATA664251 implements this device, too). The chip measures 5 by 5 mm in its QFN32 package.
The ATA664251 system-in-package device (7mm-by-7mm QFN48) incorporates an ATA664151 plus an Atmel AVR 8-bit ATtiny167 microcontroller. The low-power, RISC-based ATtiny167 MCU combines 16kB flash memory, 512B EEPROM, 512B SRAM, 16 general-purpose I/O lines, and 32 general-purpose working registers. Atmel says this combination enables the development of simple and inexpensive, yet powerful, nodes for ambient lighting and switch scan applications.
Single Die
Also debuting at electronica was Melexis’ MLX81106, a LIN RGB LED slave that occupies a single die in a 5mm-by-5mm fused leadframe SOIC 8 package (Fig. 3). The device includes a physical-layer LIN transceiver, LIN controller, voltage regulator, and 16-bit RISC-based microcontroller. Packed into the LIN controller is a 32kB flash memory, allowing each of the four outputs to be programmed up to a maximum of 35mA. A total of 1024 colours can be generated.
Michael Bender, product line manager for LIN & Power Control at Melexis, is adamant that there’s a demand for user-controllable vehicle interior lighting. “It is the car manufacturers that are asking for this,” he says. “The market driver behind it seems to be car customers.”
Bender explained that the MLX81106’s high level of integration makes for easy implementation of RGB LED ambient light modules. Since a primary reason for using LIN is to reduce cabling weight in vehicles, the size and weight of the LIN modules is particularly important, especially because there will be multiple nodes. That makes the MLX81106’s small SOIC8 package desirable in this scenario.
The device also incorporates an ADC, 16-bit PWM generation, and an LED threshold-monitoring capability. The LIN protocol handler meets all LIN standards, including LIN2.x as well as SAE J2602.