Melexis introduces 24-channel automotive LED driver

Melexis has introduced the MLX81132, a programmable automotive LED driver combining 24 constant-current channels, local processing, and two-way multiplexing to control up to 48 individual light sources from one integrated circuit.

The device supports up to 16 RGB pixels and is intended for animated interior lighting in dashboards, door panels, seats, centre consoles, and other illuminated cabin surfaces. Its architecture concentrates lighting control functions within a smaller number of integrated circuits, reducing the need to provide dedicated driver electronics at every individual pixel.

Modern vehicle interiors increasingly incorporate distributed lighting systems containing numerous RGB emitters. These can provide decorative illumination, communicate operating states, and support visual interactions between the vehicle and its occupants.

As the number of independently controlled light sources increases, the supporting electronic architecture must accommodate additional driver circuits, communications connections, processing capacity, and electrical power distribution. Lighting systems containing hundreds of pixels can therefore become relatively complex even though each individual LED performs a simple function.

The MLX81132 uses 24 constant-current output channels combined with two-way multiplexing. In this arrangement, the available drive resources can address two groups of connected LEDs, allowing the integrated circuit to control 48 individual emitters rather than being limited to 24.

Because an RGB pixel typically contains separate red, green, and blue emitters, the 48 individually controlled channels correspond to 16 RGB pixels. The resulting arrangement reduces the amount of dedicated driver circuitry required for a given number of pixels compared with architectures that integrate a driver into every light source.

Multiplexing requires the controller to coordinate current delivery between connected LED groups. The switching arrangement, drive current, and timing must be managed to maintain the intended brightness and visual appearance without introducing unwanted flicker or inconsistent illumination.

Melexis specifies configurable LED currents of up to 80mA from a 5V supply. The device also supports channel bundling where an application requires higher peak LED current, allowing its output resources to be configured for different lighting arrangements.

Brightness control uses 16-bit pulse-width modulation, providing fine control over the proportion of each switching period during which an emitter receives current. Adjusting the relative brightness of the red, green, and blue elements allows the controller to generate different colours and animated lighting effects.

Colour consistency introduces another engineering requirement because individual LEDs can exhibit different electrical and optical characteristics. Devices from different manufacturing batches or suppliers may produce slightly different light output under nominally identical drive conditions.

Temperature changes can also affect the output of LED emitters. Maintaining a consistent displayed colour therefore requires the control system to account for both the calibrated behaviour of individual devices and changes occurring during operation.

The MLX81132 provides local calibration storage and individual LED temperature compensation. Its integrated non-volatile memory can retain calibration information, enabling the controller to apply corrections without relying entirely on an external processor.

Local processing is handled by an integrated 16-bit RISC microcontroller containing 64KB of Flash memory, 8KB of RAM, and 640 bytes of non-volatile memory. The controller can execute lighting functions and colour calculations close to the connected emitters.

This arrangement reduces the amount of lighting-specific processing that must be performed by a vehicle’s external electronic control unit. It also allows developers to implement application behaviour within the driver itself rather than requiring every lighting operation to be calculated elsewhere in the vehicle.

The device uses Melexis’ MeLiBu 2.0 communications system, which supports adjustable data rates up to 4Mbit/s. MeLiBu is a bus-based arrangement designed for distributed automotive lighting, allowing individual driver ICs to be addressed and coordinated across different physical locations.

This differs from lighting architectures in which control information must pass sequentially through each individual pixel. A bus-based system allows multiple lighting modules to receive appropriate control information without every intermediate pixel acting as the next communications link.

Bus extension functionality also supports arrangements distributed across several printed circuit boards. Such systems may be required where lighting sections are installed in separate vehicle panels but must operate as part of a coordinated animation or display.

The MLX81132 additionally includes support for 10BASE-T1S endpoint applications, relevant to automotive architectures using shared Ethernet connectivity. That support is distinct from the device’s MeLiBu 2.0 physical layer, and the two communications capabilities should not be treated as interchangeable.

Increasingly centralised vehicle electronics can require lighting modules to communicate with higher-level controllers while retaining local control over individual LEDs. The MLX81132 is intended to support such arrangements, including applications associated with zonal electrical architectures.

Diagnostic functionality includes open-load, short-circuit, and temperature monitoring. An integrated 12-bit fully differential analogue-to-digital converter supports measurements including LED forward voltage, while SPI and I²C interfaces provide additional connections to external devices.

These functions allow the controller to identify electrical conditions affecting individual emitters or the surrounding circuitry. Diagnostic information can be used by the wider vehicle system when assessing lighting faults, although the response to a detected fault depends on the completed system design.

Melexis has developed the device according to ISO 26262, with support for automotive applications up to ASIL B as a Safety Element out of Context. It is also specified to AEC-Q100 qualification requirements.

The Safety Element out of Context classification provides information relevant to integrating the IC into a safety-related design. It does not, by itself, establish that an entire vehicle lighting system satisfies a particular Automotive Safety Integrity Level.

The MLX81132 is supplied in a 5mm-square QFN40 package with wettable flanks. The compact package and high channel density allow the control circuitry to be positioned within distributed lighting modules where PCB area can be limited.

According to Melexis, the device can support lighting response latency down to 2ms under the specified operating arrangement. Actual behaviour in a completed vehicle will also depend on system communication, software configuration, and the timing of the lighting functions.

The MLX81132 is the first member of a planned generation of MeLiBu LED drivers. Melexis intends to extend the family with additional devices, including code-free versions and products for exterior automotive lighting.

Samples of the programmable MLX81132 are currently available. Equipment manufacturers can use the device for initial hardware integration and software development, with production applications requiring validation of the LED arrangement, thermal characteristics, communications behaviour, and applicable automotive qualification requirements.