Texas Instruments (TI) Inc. has claimed the industry’s smallest and most accurate 1.5-W isolated DC/DC bias-supply module with an integrated transformer. By delivering more than 1.5 W at ambient temperatures of 105°C, the UCC14240-Q1 high-voltage DC/DC module can power isolated gate bipolar transistors (IGBTs) as well as silicon carbide (SiC) and gallium nitride (GaN) switches at high frequencies.
By integrating the transformer in an IC, it enables the reduction of size, weight, and height of the power system. The UCC14240-Q1 uses a proprietary integrated transformer technology that can shrink power solutions by 50 percent, according to TI. This also translates into lower costs for high-voltage environment applications such as electric vehicle (EV) and hybrid EV power-train systems, motor-drive systems, and grid-tied inverters.
(Source: Texas Instruments)
TI’s products are addressing the challenges of reducing the cost and improving the range of EVs and is doing it in a couple of different ways, said Ryan Manack, TI’s director of automotive systems, Systems Engineering Marketing, during a virtual presentation. “We’re trying to integrate as much as possible at the product level and the system level where we have technologies that allow powertrain systems to be integrated into two-in-one and three-in-one type systems with onboard chargers, traction inverters, DC to DC converters, etc.,” he said.
This helps customers reduce costs, simplify the design, streamline the functional safety compliance to get to market faster, and overall improve the reliability of these systems, Manack said. “This integration can also extend the drive range and add to the efficiency [of EVs].”
One of TI’s goals is to reduce the number of parts in the power solutions, including components and at the architecture and system levels. This simplifies the designs to make the integration easier by reducing the number of electronic boxes that have to go inside the automobile, said Manack.
“While we’re doing that, how do we get the 98% system efficiency and help customers strive towards 99% efficiency, reduce loss, reduce heat, operate more efficiently, operate at higher frequencies, and reduce the size of the magnetics, then ultimately through this integration increase the system reliability and optimize the thermal performance,” he added.
Bias power architecture
Traditional bias power architectures used in EVs use one transformer and a single bias controller to generate the bias voltages for all the gate drivers. Today, customers are moving to distributed architecture systems to leverage advantages around redundancy and reliability due to safety concerns and the need for space- and weight-savings
“The question is ‘how do you bias the isolated gate drivers in the system,’” Manack said.
“Biasing really means how do we provide the power to the secondary side of these isolated gate drivers to drive the IGBT or the SiC switch, or even GaN switches on the high-voltage side to increase frequency and reduce size,” said Manack. “In legacy systems, you could potentially use one transformer to bias all of these gate drivers, but in automotive systems where redundancy is key and where small size and weight is key, we see more customers moving to a distributed power architecture where every isolated gate driver has a dedicated bias supply.”
So, if one bias supply fails, the other bias supplies remain operational along with their paired gate drivers, which improves vehicle safety on the road, said TI.
Click for a larger image. (Source: Texas Instruments)
The UCC14240-Q1 is designed to help engineers take advantage of the distributed architecture. The dual-output power module offers 60% efficiency – twice that of traditional bias supplies – doubling the power density and helping increase vehicle driving range, said TI.
Click for a larger image. (Source: Texas Instruments)
With a small footprint of 12.8 × 10.3 mm and 3.55-mm height, the UCC14240-Q1 enables designers to reduce the power solution area by as much as 50%, with more power in half the size. This enables automakers to achieve the highest power density and 98% system efficiency. Another advantage of the height reduction is the flexibility to place the module on either side of the printed circuit board (PCB).
TI is heavily focused on power density, which means shrinking the size of the total solution, and one component that “always stuck out literally was the transformer, which is used as the bias supply for those isolated gate drivers,” said Steve Lambouses, vice president and general manager, high voltage power at TI.
Through a proprietary technology TI has integrated the transformer into the UCC14240-Q1, which is very timely as the industry is moving towards a distributed architecture, said Lambouses. The integrated transformer provides power delivery over a wide temperature range and maintains 3,000-VRMS isolation, compared to legacy flyback or push-pull architectures using a traditional power transformer with 2,000 VRMS isolation, he said.
[TI’s UCC12050 isolated DC/DC bias power supply, introduced in 2020, was TI’s first IC to use the integrated transformer technology.]
The UCC14240-Q1 reduces the bill of materials from 26 to 10 devices using the proprietary transformer technology and it is also the industry’s smallest and most accurate, which is also important because of the faster SiC and GaN switches, he added.
In addition to integrating a lot of the external components in the power solution, the UCC14240-Q1 enables higher frequency switching in a smaller package.
Isolated power transfer in an IC-sized package: Legacy push-pull architecture with bulky transformers in a 11-mm height (left) and the UCC14240-Q1 with an integrated transformer in a 3.55-mm height package (right). (Source: Texas Instruments)
Moving away from a traditional flyback or push-pull architecture with one large transformer to a distributed architecture with the UCC14240-Q1 allows for scalability and other benefits such as the capability to use soft-switch technology that will reduce EMI, said Lambouses.
The 3.5-pf primary-to-secondary capacitance of the UCC14240-Q1 is what really allows for a completely different control algorithm external to the chip and the move to a soft-switching control scheme, he said. The UCC14240-Q1 can mitigate EMI caused by high-speed switching and achieve common-mode transient immunity (CMTI) performance of more than 150 V/ns.
The DC/DC module also enables easier compliance to electromagnetic compatibility standards of Comité International Spécial des Perturbations Radioélectriques (CISPR) 25 and CISPR 32, due to features such as soft switching, spread-spectrum modulation, shielding, and low parasitics.
The UCC14240-Q1 also has an integrated closed-loop control with ±1.0% accuracy over the temperature range of -40°C to 150°C. The device’s tight tolerance enables the use of smaller power switches while also improving overcurrent protection, said TI.
The device eliminates the need for an external optocoupler, traditionally used in flybacks and push-pull systems in order to achieve very high accuracy, said Lambouses. This also removes the reliability and temperature limitations of the optocoupler in the design, he said.
The 1% regulated accuracy is great for IGBTs, said Manack. “But it’s critical for the wide-bandgap devices – SiC or GaN – that have more gate sensitivity and more RDS(on) variation as a function of gate voltage.”
The UCC14240-Q1 includes other feature such as on-chip protection, including fault monitoring as well as overcurrent, overpower, and overtemperature protection. It offers third-party-certified 3-kVrms isolation and is said to deliver the industry’s best vibration immunity due to its ultra-low weight and 3.55-mm height.
The UCC14240-Q1, in a 36-pin, 12.8 × 10.3 × 3.55-mm shrink small-outline package, is available in pre-production quantities from TI. Pricing starts at $4.20 in quantities of 1,000. An evaluation board, the UCC14240Q1EVM-052, is available on TI.com for $59.
TI is demonstrating the UCC14240-Q1 at the TI Live! Tech Exchange virtual event, Sept. 27-29, 2021.
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