Power Electronics Europe Issue 4 - November 2022

www.MonolithicPower.com AUTOMOTIVE POWER SUPPLY DESIGN 19 www.power-mag.com Issue 4 2022 Power Electronics Europe How to Design a Thermally Balanced Current-Sharing System for Multi-Phase Power Designs The car of tomorrow is envisioned to be an audiovisual wonderland on wheels, including wraparound screens and dozens of speakers. Driving on the road in the future will immerse passengers in an incredible sensory experience with content streamed via ultra-fast 5G. To achieve this content-rich, connectivity-heavy paradigm of future mobility, emerging digital cockpit systems continue to demand exponentially greater computing capability. These increasing computing requirements consequently result in a demand for higher power. This article proposes a novel, cost-effective approach to achieve a high-power, offline battery (12 V) power management stage that multi-phases two buck controllers. Xavier Ribas, Applications Engineer, MPS, USA As such, interleaved topologies are gaining popularity because they can supply higher load currents while improving EMC. However, engineers must optimize the balance between thermals, board size, and cost when designing these automotive power management systems. In particular, it is vital to achieve optimal current sharing between phases to avoid overheating the MOSFETs in one phase, as this can degrade the entire system. The proposed solution combines a simple yet elegant thermal-balancing circuit with two interleaved MPQ2908A-AEC1 devices, which are 4 V to 60 V input, current-mode, synchronous step-down controllers. This system effectively improves current sharing between phases while adeptly addressing the higher power dilemma. Power stage As the power demand of new automotive designs continues to rise, power electronic engineers face the challenge of designing circuits that can deliver more power without increasing PCB size and cost. In addition, these circuits must maintain low EMI below the regulated values. Multi-phase topologies provide a simple solution to overcome this design challenge. In a multi-phase topology, multiple power converters are placed in parallel to increase the available load current of the entire power supply unit (PSU), which increases the amount of deliverable power. Moreover, if all of the converters run synchronously with each other but in different locked phases, then the EMI generated by the overall system is decreased. Lastly, the current demanded by the load is shared by all of the converters, which optimizes thermal behavior. The automotive power management system presented in this article uses a dual-phase power supply that steps down the 48 V common in new automotive designs to the 12 V that is demanded by many advanced driver assistance systems (ADAS). To incorporate high 20 A load currents, this design uses two MPQ2908A- AEC1 devices. In addition to this controller’s wide input range, which can step down from the 48 V specification, this device can be implemented in dual-phase topologies using its SYNCO pin, which outputs a 180° out-of-phase clock. Figure 1 shows the system’s block diagram for the original 240 W power stage. First, there is a 48 V car battery. Second, a system with reverse polarity protection and over-voltage protection (OVP) is added to protect the system from damage in the event of undesired events (e.g. incorrect cable connections). Lastly, an EMC filter reduces the conducted emissions, while the dual-phase interleaved buck converter steps down the voltage from 48 V to 12 V. Since the power managed by the system is quite high, a frequency spread spectrum (FSS) Figure 1: Original 240 W power stage