Multi-phase SPI boost controller for flexible automotive headlight systems

Diodes Incorporated’s AL8859Q is an automotive-compliant* multi-phase SPI boost controller is designed to meet the power density, efficiency, EMI, and functional safety requirements of advanced headlight control units. The device serves as the primary constant-voltage pre-stage for adaptive front lighting systems, including high beams, low beams, daytime running lights (DRL), turn indicators, fog lights, and cornering lights, as one integrated lighting module. The AL8859Q also addresses broader power systems for automotive applications.

The AL8859Q integrates a current-mode multi-phase boost architecture with a wide 4.5V to 60V input voltage range, enabling operation across standard 5V, 12V, 24V, and 48V supply rails. It also improves output voltage tolerance under load dump and transient conditions through programmable registers. A single device supports two phases; scaling to three or four phases requires synchronising devices. This makes it suitable for 100W to 400W output power with a balanced thermal distribution, low ripple current, and system efficiency of ~95%, while minimising external component stress by using Diodes Incorporated’s automotive-compliant discrete components, including MOSFETs, SBRs, and TVS diodes.

The SPI digital interface programs the register map to control output voltage, switching frequency, current limits, and protection thresholds. Such software programming, flexibility, and reconfiguration allow for a single hardware platform design to be adapted across multiple vehicle applications. Integrated one-time programmable memory enables production line configuration and fail-safe or stand-alone operation, reducing MCU dependency and making system operation more robust. The device includes extensive diagnostics, including thermal warning and shutdown, overvoltage and undervoltage protection, current limiting, SPI error detection, and VDRIVE monitoring. This enables continuous system status reporting and facilitates functional safety-capable** compliance.

The AL8859Q incorporates spread-spectrum frequency modulation to ease compliance with CISPR 25 Class 5 EMI requirements, reducing the need for bulky external filtering and lowering overall BOM costs. The device boasts a voltage accuracy of ±0.5% at 50V (typ.), ensuring a stable supply for downstream LED drivers with high-current accuracy. This improves light consistency and reliability across operating conditions.

Housed in a compact wettable flank V-QFN4040-24/SWP package measuring 4mm x 4mm, the device optimizes PCB space while enabling automated optical inspection to ensure solder joint reliability.

* Automotive-compliant – AEC qualified, manufactured in facilities certified to IATF 16949, supporting PPAP documents.

** Functional safety-capable – FuSa FIT, FMD, and Pin FMA provided to assist in ASIL systems.