January 24, 2019
| By: Christine Young
Blogger, Maxim Integrated
The smartphone-like experience inside today’s vehicles comes at a computing power price. From always-on digital instrument clusters to infotainment hubs and fusion electronic control units (ECUs), these applications rely on sophisticated algorithms and computations that need high levels of compute power from the processors. In the recent past, a typical automotive system-on-chip (SoC) consumed 20W of power. Now, you’ll need to be prepared to support hundreds of watts of power from multiple chips. This means that managing their power supplies requires a delicate balance that addresses demands such as low power consumption, high efficiency, and electromagnetic interference (EMI) mitigation.
There are two key considerations here:
Figure 1. Vehicle subsystems like heads-up displays, pictured here, need high levels of compute power, as well as efficient power supplies to manage the processors.
Automotive power-management ICs (PMICs) need increased gate drive, dynamic voltage scaling, and superior transient performance to optimize performance of the SoCs. For buck controllers, this creates the need for a strong gate drive that can drive input for the gate of a high-power MOSFET. Also important for the power components is high efficiency. One way to achieve this is to select power supply components with low quiescent current, as keeping this standby current at a minimum for always-on parts can lower overall power consumption. Good thermal performance, minimal power loss, and cooler operating temperatures are other characteristics to look for when evaluating parts for these high-voltage applications.
EMI mitigation is always important given the harsh electrical environment of the vehicle. Automotive OEMs are responsible to making sure that the electronic subsystems in their vehicles do not emit excessive EMI and that these systems aren’t unduly affected by noise from other subsystems. There are various techniques to address EMI, but many do come with tradeoffs. For example, using components with more capacitance dampens voltage ripples with load transients; however, automotive-qualified components with more capacitance are expensive. Another tactic is to use shield the subsystem from radiation with metal enclosures, but this approach adds cost and weight to the design.
Typically, the PMICs for high-voltage automotive applications are attached to the vehicle’s lead-acid battery. This battery operates in the 9V to 16V range, but has transient conditions that can cause it to go as low as 4V and as high as 40V. So, the PMICs should be able to handle high input voltages as well as load dump events through the vehicle’s lifetime. Converters are ideal for power supplies that require less than 6A to 8A of current, while controllers are suited for applications that are 10A or higher because they have external FETs. External FETs have much lower RDS(ON) compared to converters with integrated FETS, which results in higher efficiency and better thermal dissipation.
Converters today are limited by the cost, efficiency, and thermal dissipation inside the package. Typically, controllers come at a larger solution size and the external FETs also make addressing EMI more challenging. Maxim recently expanded its portfolio of automotive PMICs with new high-voltage buck converters and high-voltage, multiphase controllers that overcome the key power supply design challenges discussed in this post. The buck converters can manage DC power in applications with simpler, less powerful processors, while the buck controllers are ideal for applications with more powerful processors. A new white paper, “Addressing the Challenges of High-Voltage Automotive Power Applications,” discusses how the MAX20004/6/8 synchronous buck converters, the MAX20034 dual synchronous buck controller, and the MAX20098 synchronous buck controller address the design challenges of high-voltage automotive applications. Read the paper today for a more detailed look at how you can create high-performing digital cockpit designs that aren’t a drain on the power supply.