Today’s car buyers, whether purchasing premium or economy models, expect to charge multiple devices simultaneously through in-vehicle USB ports. To meet this demand, automakers are replacing legacy USB Type-A ports with multiple USB Type-C ports that support the latest USB power delivery (PD) standards. These standards enable significantly higher power levels—up to 48 V and 240 W—suitable for fast-charging laptops, tablets, and phones.
USB PD controllers operate alongside internal or external DC/DC converters, which add their own thermal stress to the system. This challenge becomes even more critical in automotive, industrial, and other space-constrained designs where airflow is minimal and ambient temperatures are high. If left unmanaged, excessive heat can damage or degrade system reliability. Elevated temperatures accelerate the aging of semiconductors and passive components, cause solder joint fatigue, and, in the worst cases, can lead to printed circuit board (PCB) delamination or thermal runaway. These risks make thermal management a priority in system-level USB PD designs, especially when long-term reliability or safety are requirements. In this power tip, I’ll explore different methods to manage heat and improve system reliability when implementing automotive USB PD solutions.
A typical 12-V battery automotive system needs these components to implement a USB PD charging port:
- A DC/DC converter. The converter steps the 12-V battery voltage up to the desired USB output (commonly 5 V to 20 V, up to 60 W, or even 48 V and 240 W with the latest USB PD specifications).
- A controller that supports USB PD. This controller is at the heart of modern high-power charging systems, negotiating power roles and voltage levels with connected devices. The TPS26744E-Q1 from Texas Instruments (TI) is an example of a dual-port automotive controller that manages USB PD profiles and controls the associated DC/DC converter.
Challenges when designing high-power USB PD from a 12-V rail include:
- Wide voltage variations: Both input (car battery) and output (USB Type-C port and connected load) voltages vary significantly, requiring a reliable and flexible power architecture.
- High current requirements: Delivering 100 W from a 12-V input can require more than 10 A of input current, necessitating large inductors, low drain-to-source on-resistance MOSFETs, and careful PCB layout to manage losses on the power components.
- Thermal bottlenecks: Most designs use buck-boost converters with four external MOSFETs, which can introduce substantial thermal stress under high load conditions, especially at low input voltages and high output power.
The shift to 48-V systems
The automotive industry is transitioning toward 48-V power architectures, which simplifies USB PD designs and improves thermal efficiency. With a higher input voltage, a buck-only topology is sufficient, replacing the more complex buck-boost design. You’ll need fewer external components (no four-FET bridge, and with significantly reduced inductor size and current rating requirements).
For example, TI’s LM72880-Q1 is an integrated automotive-grade buck converter suitable for 48-V input USB PD applications. Figure 1 shows two USB PD DC/DC converters: a buck-boost converter off a 12-V battery to the left and a buck converter only off a 48-V battery to the right. You can see that the total solution size and components are much lower for the 48-V based system. The 48V-based solution achieves a 58% reduction in PCB area, from 1.75 in² to 0.74 in².
Figure 1 Buck-boost topology for 12-V architecture versus a buck-only topology for the 48-V architecture. Source: Texas Instruments
Lower switching frequencies can help
Switching frequency has a direct impact on power loss. Higher frequencies reduce the size of passive components but increase switching losses in MOSFETs; lower frequencies reduce switching losses but increase inductor ripple, and may require larger output filters.
Figure 2 compares the same board working at different switching frequencies, with 400 kHz to the left and 200 kHz to the right.
Figure 2 Thermal images of the same board working at a switching frequency of 400 kHz (left) versus 200kHz (right). Source: Texas Instruments
The thermal test comparing a 400 kHz versus 200 kHz switching frequency (both at a 54-V input, 5-A output, and with fan cooling) shows that lowering the frequency reduces converter temperature by 18°C. The inductor temperature does rise slightly from 60°C to 63°C, indicating the need for output filtering to balance the heat distribution.
Thicker copper, more PCB layers
PCB design plays a crucial role in thermal management. Increasing copper thickness and adding more layers can significantly reduce temperature rise, especially when fan cooling is not available.
Figure 3 shows thermal images from two similarly sized boards. The board on the left is four layers, each with 1 oz of copper. The board on the right is six layers, with 2 oz of copper for the top and bottom layers and 1 oz of copper for the inner layers.
Figure 3 Thermal images of two PCBs: one with four layers with 1 oz of copper each (left) and one with six layers with 2 oz outer layers and 1 oz inner layers (right). Source: Texas Instruments
Both boards operate at a 48-V input and a 20-V output with 400 kHz switching. The board on the right carries 5 A versus 4.25 A for the board on the left, yet experiences 50% less temperature rise from improved heat dissipation. This underscores the importance of investing in copper-heavy PCB stacks for thermally demanding automotive applications.
Thermal foldback
Traditional protection methods often rely on thermal shutdown, completely disabling the system when a temperature threshold is crossed. While thermal shutdown protects hardware, this approach is abrupt and disruptive. In applications where continuous operation is preferable to complete shutdown—such as in automotive infotainment, industrial USB charging, or consumer docking stations—thermal shutdown simply doesn’t provide a good user experience.
USB PD controllers today, including those from TI, support firmware-configurable thermal foldback, a more sophisticated, dynamic thermal response system that reduces power delivery as temperature rises. Instead of cutting power entirely, the controller steps down the VBUS output power, allowing the system to cool while still maintaining basic functionality. It’s a “fail-soft” approach that maintains safety and system uptime.
TI’s USB PD controllers monitor system temperature through an external negative temperature coefficient thermistor connected to an analog-to-digital converter input. The firmware evaluates this voltage to assess temperature conditions. As the temperature rises, the system progresses through configurable thermal phases, each with increasing levels of power reduction.
In Figure 4, thermal foldback is divided into three thermal phases, each representing a higher level of thermal severity:
- Phase 1: Mild temperature rise. Power is reduced slightly to reduce thermal buildup.
- Phase 2: Intermediate temperature. Power delivery is throttled further to stabilize the system.
- Phase 3: High-temperature alert. Power is significantly reduced or disabled to avoid dangerous overheating.
Figure 4 Thermal thresholds rising and falling with three main phases of thermal foldback. Source: Texas Instruments
Each phase is defined by two voltage thresholds: a rising (Vth_R) and falling (Vth_F) threshold, creating hysteresis to prevent rapid toggling between phases when temperatures hover around a transition point.
In response to phase transitions, the USB PD controller will renegotiate the USB PD contract with the connected sink device. The maximum power allowed in each phase is configurable, offering precise control. For example, if the maximum port power is 100 W, thermal foldback could reduce the power to 60 W when entering phase 1, 27 W in phase 2, and 7.5 W in phase 3.
Thermal foldback is no longer a luxury feature; it’s a necessity in high-power USB PD designs. With firmware-configurable behavior, TI’s USB PD controllers give engineers the flexibility to maintain safe, efficient operation under thermal stress without sacrificing usability or system availability. By stepping power down intelligently instead of shutting off entirely, thermal foldback improves product reliability, extends component life, and delivers a better end-user experience in demanding environments.
USB PD thermal management
Thermal management is an important design consideration in automotive USB PD applications. By leveraging higher-voltage systems, optimizing switching frequency, and investing in PCB design, you can significantly reduce heat-related stress and improve overall reliability. TI offers a range of automotive-grade USB PD controllers and DC/DC converters, such as the TPS26744E-Q1 and LM72880-Q1, to help you design compact, efficient, and thermally reliable USB Type-C charging solutions.
Josh Mandelcorn has been at Texas Instrument’s Power Design Services team for two decades focused on designing power solutions for automotive and communications / enterprise applications. He has designed high-current multiphase converters to power core and memory rails of processors handling large rapid load changes with stringent voltage under / overshoot requirements. He previously designed off-line AC to DC converters in the 250W to 2 kW range with a focus on emissions compliance. He is listed as either an author or co-author on 17 US patents related to power conversion. He received a BSEE degree from the Carnegie-Mellon University, Pittsburgh, Pennsylvania.
Seong Kim is an Applications Engineer at Texas Instruments, where he focuses on automotive USB Power Delivery and DC/DC converter solutions. With over a decade of experience at TI, Seong has supported a wide range of embedded and power designs – from Wi-Fi/Bluetooth MCUs for IoT to high-speed USB-C and PD systems in automotive environments. He works closely with automotive OEMs and Tier-1s to enable reliable fast-charging systems, and is regarded as a go-to expert on PD integration challenges. Seong has authored technical collateral and training materials used across TI’s global customer base, and is listed as an inventor on a pending U.S. patent related to USB Power Delivery. He holds a BSEE from the University of Texas at Dallas and is based in Dallas, Texas.
Stefano Panaro is a Systems Engineer in Texas Instrument’s Power Design Services team focused on designing power solution for Automotive and Communications applications. His main focus is on the design of DCDC converters, with a power level ranging from mW to kW. He received his BS in ECE and his MS in Electronic Engineering from Politecnico di Torino, Italy.
Related Content
- A quick and practical view of USB Power Delivery (USB-PD) design
- USB Power Delivery: incompatibility-derived foibles and failures
- Power Tips #130: Migrating from a barrel jack to USB Type-C PD
- Power Tips #75: USB Power Delivery for automotive systems
- Power Tips #142: A comparison study on a floating voltage tracking power supply for ATE
Additional resources
- For more information, see the reference design from TI, “Automotive, 24V to 60V input, two-port USB Power Delivery 60W maximum per port reference design.”
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