Further challenges for electric vehicles will include cost factors, as the price of batteries—the most crucial component of electric vehicles—is continuously decreasing. At the same time, other parts of electric vehicles also need to further reduce costs to accelerate their widespread adoption.
“TI’s goal is to reduce production costs for automakers and purchase prices for consumers. TI’s technology and expertise can help customers integrate powertrains to reduce costs, simplify design, improve functional safety, and enhance reliability. Powertrain integration also enables extended drive range, improved system efficiency, and increased power density by achieving higher power in smaller solutions,” said Ryan Manack, Director of Automotive Systems Engineering and Marketing at Texas Instruments.
TI focuses on helping OEMs reduce total costs and shorten the profitability cycle for original equipment manufacturers (OEMs). Today, TI's philosophy for electric vehicles is Design to Cost (DTC), which focuses on powertrain integration, i.e., placing power electronic components more compactly, reducing the number of components, and integrating them into fewer boxes.
Ryan used the isolated bias power supply recently launched by TI as an example to introduce the specific implementation of TI's DTC concept.
Let's start with quarantine
Electric vehicle powertrain systems include different buses such as high-voltage circuits and digital control communication. Therefore, in order to ensure safety and high signal reliability, a large number of isolation devices are needed for digital interfaces or for isolating power supplies between high and low voltage.
To achieve highly integrated isolation, TI has developed two integration technologies: one using SiO2 for isolation in digital channels, and the other integrating ultra-thin transformers. Both technologies have been successfully commercialized. SiO2 technology is used in markets including digital isolators, isolated interfaces, isolated amplifiers, isolated gate drivers, and isolated ADCs, while integrated transformer technology is used in isolated DC/DC modules and signal isolators for integrated power supplies.
TI's isolation technology is now widely used in markets including digital isolators, isolated power supplies, isolated interfaces, isolated ADCs, isolated amplifiers, and isolated gate drivers, meeting the diverse needs of automotive and industrial applications. TI offers products with different isolation levels, including basic (3kVRMS) and enhanced (5kVRMS).
Taking traction inverters as an example, there are numerous subsystems involving isolation.
The power architecture of electric vehicles is changing.
As requirements for safety, power density, and electromagnetic interference (EMI) become increasingly stringent, different power architectures have emerged to address these challenges, one of which is a distributed power architecture that equips each critical load with an independent bias power supply.
The traditional approach is a centralized power architecture, which uses a central transformer and a bias controller to generate bias voltages for all gate drivers.
Hybrid electric vehicles / electric vehicles with different types of drive power architecture
Centralized architectures have historically been popular due to their lower cost, but they are difficult to manage for faults and regulate voltage, and their layout is challenging. Centralized architectures are also more susceptible to noise, and components within a single system area are taller and heavier. Furthermore, centralized architectures lack power redundancy; a single component failure in the bias power supply can lead to a large system failure.
Distributed architecture offers enhanced reliability and security by assigning a dedicated, local, and easily adjustable bias power supply to each gate driver, meeting the reliability requirements of electric vehicle applications. This provides redundancy and improves the system's responsiveness to single points of failure. For example, if one of the bias power supplies associated with a gate driver fails, the other five bias power supplies and their associated gate drivers can still operate normally. If five of the six gate drivers remain operational, the motor can be effectively decelerated and shut down, or may continue running. With this power system design, passengers in the vehicle may not even be aware of the problem.
There is also a semi-distributed architecture that falls somewhere in between.
Because distributed architectures have more isolated bias power supplies, their cost and design complexity are completely different from traditional centralized architectures.
The traditional approach to generating isolated power supplies involves using a DC/DC converter to drive a transformer in flyback, fly-buck, or push-pull topologies. The pulsating signal on the secondary side is rectified and filtered to generate the isolated DC power supply. Line and load regulation is achieved through primary-side feedback based on an optocoupler. In some cases, when the DC/DC converter is operating in an open-loop configuration, an LDO is used for post-regulation of the converter's output. A drawback of this discrete approach is that the complete solution (transformer and other components) occupies significant space on the circuit board. Furthermore, designing a stable and efficient isolated power supply is challenging.
TI's solution integrates a DC/DC converter with a miniature transformer in a single package. This type of solution addresses several design challenges faced by system engineers, significantly reducing board area: the first advantage of an integrated solution is the reduction in board area. Power stages, transformers, rectifier diodes, isolation feedback (and sometimes digital data isolation channels) are all integrated into the same device, resulting in a significantly smaller solution size. In addition to reduced surface area, using planar transformers allows integrated solutions to have a lower z-dimensional (height) than discrete transformers, which are two to three times thicker. Simultaneously, high integration provides a clean and reliable design. Integrated solutions simplify system design because users can integrate line/load regulation feedback and all power supply protection mechanisms (such as overload and short-circuit protection, thermal shutdown, and soft start) on the chip. Boards with bulky transformers perform poorly in vibration testing, especially for automotive systems, where the complex vibration and shock environments can cause transformer detachment or poor soldering. Therefore, integrated solutions also contribute to improved board-level reliability.
TI's planar highly integrated transformer technology offers numerous advantages.
1.5W Isolated Bias Power Supply IC
Integrated transformers, due to size limitations, typically provide only limited power. TI's newly released UCC14240-Q1, a smaller and more precise isolated DC/DC bias power supply IC, can provide up to 1.5W of power. It integrates a transformer and DC/DC controller with a proprietary architecture, achieving high efficiency and extremely low radiation, with an isolation performance of 3000-VRMS.
With a thickness of only 3.55mm, the UCC14240-Q1 is compact, allowing designers to reduce the size of their power solutions by half and support greater power output in half the dimensions. Its slim design also allows the module to be mounted on either side of the printed circuit board, providing engineers with ample flexibility.
This dual-output power module boasts an efficiency of 60%, twice that of conventional bias power supplies, resulting in double the power density and contributing to increased vehicle range. At an ambient temperature of 105°C, the UCC14240-Q1 delivers over 1.5W of power, enabling engineers to drive IGBTs, silicon carbide (SiC), and gallium nitride (GaN) switches at high frequencies.
This module integrates on-chip device protection, comprehensively integrating soft-start protection, fault monitoring, overcurrent protection, overpower protection, and overheat protection. It also provides a dedicated power supply pin, allowing the MCU to sense output adjustments. This pin can also provide fault alarms for the system.
The UCC14240-Q1, combined with a 3.5pF primary-to-secondary capacitor, reduces EMI generated by high-speed switching and easily achieves common-mode transient immunity (CMTI) performance exceeding 150V/ns, which is particularly important for high-frequency SiC and GaN applications.
The UCC14240-Q1 features soft switching, spread spectrum modulation, shielding, and low parasitics, making it easier to meet the electromagnetic compatibility standards of the International Special Committee on Radio Interference (CISPR) 25 and CISPR 32, thereby accelerating time to market. At the same time, soft switching can reduce dead time and improve system efficiency.
UCC14240-Q1 schematic diagram
The UCC14240-Q1 employs integrated closed-loop control, achieving an accuracy of ±1.0% within a temperature range of -40°C to 150°C. Compared to silicon IGBTs, SiC MOSFETs exhibit less distinct transitions between the linear and saturation regions of their output characteristic curves, resulting in rapid current rise during short circuits or overcurrents. This necessitates a faster response time for protection circuits. Therefore, short-circuit protection for SiC MOSFETs requires selecting chips with fast detection speeds and short response times for the protection circuit design. Furthermore, based on IGBT design experience, a blanking time is required each time the circuit is turned on to prevent false DSAET triggering due to the initial drop in Vce voltage. This blanking time requirement places even greater demands on the short-circuit protection circuit design of the already limited 3µs SiC MOSFET, necessitating higher accuracy in the driver chip's DESAT-related parameters for effective protection. Simultaneously, a more optimized PCB design for the driver circuit is required to minimize the impact of parasitic loop inductance.
Since different types of drives require different turn-on and turn-off voltage levels, the UCC14240-Q1 features flexible VDD and VEE outputs that can be adjusted according to product requirements.
As shown in the figure, the output voltage and power vary in different scenarios. The rich adjustment functions can meet the needs of all driver applications, thereby achieving design flexibility.
In addition to automotive applications, the UCC14240-Q1 can be used for inverter bias power supplies in fields with high requirements for isolation and reliability, as well as stringent PCB area requirements, including smart grids (such as DC charging piles) and industrial robots.
In addition, TI also launched the UCC12051-Q1, a 500mW 5kVrms isolated DC/DC IC with a single-output integrated transformer, which can also achieve high isolation and low EMI characteristics.
Other isolated power supply solutions
Whether it's a controller with an external power switch, a converter integrating one controller with multiple power switches, or a power module integrating multiple controllers, power switches, and transformers, there are many solutions that provide isolated bias power supplies. This allows them to meet the needs of different power levels and topologies.
As shown in the figure, push-pull, Fly-Buck, half-bridge, and LLC topologies can all achieve isolated power supplies. However, LLC can use smaller primary-to-secondary capacitors, and is more efficient, lower in cost, and has better CMTI and EMI performance, making it very suitable for centralized isolated power supplies.
TI's UCC25800-Q1 is an open-loop LLC transformer driver for isolated bias power supplies, integrating switching power stages, control, and protection circuitry to simplify isolated bias power supply design. The LLC topology allows for the use of transformers with higher leakage inductance but lower parasitic primary-to-secondary capacitance. This low-capacitance transformer design reduces common-mode current injection through the bias transformer by an order of magnitude. This makes the UCC25800-Q1 an ideal solution for isolated bias power supplies in a variety of automotive applications to minimize EMI noise caused by high-speed switching devices. The UCC25800-Q1 employs soft-switching operation for further EMI noise reduction.
In conclusion
Consumers will always want vehicles with lower emissions, longer driving range, greater safety and reliability, and more features at lower prices. Only continuous advancements in power electronics technology can meet the increasingly demanding requirements of electric vehicle OEMs, including innovations in power architecture and related isolated gate drivers and bias power supplies.
Switching to a distributed power architecture significantly improves reliability in isolated high-voltage environments, but the challenge lies in the increased weight and size requirements due to the additional components. Fully integrated power solutions can save system-level space and achieve lightweight design. OEMs have greater flexibility in their choices. Therefore, different isolated power supplies are available, but it's essential to understand system-level specifications such as the number of outputs, regulation requirements, output power, isolation class, operating temperature, and input voltage range. Engineers can then select a more cost-effective solution that meets all system requirements based on the specific isolated power supply application requirements.
In addition to the UCC14240-Q1 isolated power supply for distributed architectures, TI also offers controllers for other isolated topology applications. These controllers are industry-leading in terms of efficiency, EMI, CMTI, integration, and reliability. Furthermore, TI truly focuses on DTC (Distributed Technology Control) and provides more cost-effective products and solutions to meet the diverse needs of customers.
