High voltage batteries in sight!  Proceed with the isolation!

High voltage batteries in sight! Proceed with the isolation!

This article is part of the Power Management series: Learning about power density

Texas Instruments has introduced a family of solid state relays that uniquely integrate power and signal transfer into a single, ruggedly isolated chip that is becoming standard in electric vehicles (EVs).

The chips include the TPSI3050-Q1 isolated driver IC with an integrated 10V gate power supply and the TPSI2140-Q1 1,400V isolated switch that offers “industry-leading reliability” in a smaller package while reducing costs.

Jeff Morroni, head of power management research and development at TI, said automakers are building batteries into electric vehicles that have nearly 10 times the voltage of most vehicles on the road. As a result, they are also investing in “isolation” technologies to help keep everyone and everything inside safe from high voltage hazards.

Danger! High voltage!

Electronic isolation prevents excess DC and AC flow between the various building blocks of a high voltage system, while allowing signals and power to flow between them. The purpose of insulation in electric vehicles is to prevent high voltage spikes that can deliver a fatal shock or damage the electronics inside.

It is useful when transporting power between low-side and high-side devices which never need to be connected for safety reasons. Insufficient insulation also opens the door to noise and electromagnetic interference (EMI).

“Wherever there are high voltages, safety is key and high voltage is key wherever you need to transfer energy more efficiently and economically,” Morroni said, adding that in battery management and other systems in electric vehicles, “we must ensure the high voltages do not reach the chassis to avoid shock “.

Today, most electric cars have internal architectures that can handle 400V of energy from a battery pack, a step up from the 12 and 48V systems that dominate cars today. But now 800V batteries are becoming standard to increase the range of electric vehicles and reduce charging times.

Each system in the electric vehicle is connected to the high voltage battery pack. But delicate electronics, such as microcontrollers (MCUs) and other chips that control systems in the EV, only require several volts.

TI is investing more in isolated power supplies and other automotive chips such as the TPSI3050-Q1 and TPSI2140-Q1. These types of devices help electronics safely sip the torrent of energy flowing on the main power bus and communicate with electric motors and other high voltage, fast transient systems.

Chip isolation

Designing for high reliability in high voltage electric vehicles typically requires the use of bulky, heavy and therefore expensive components such as transformers and relays to control dangerous voltages and currents.

But as electric car systems become more compact, the components within them also need to be closer together. This presents new design challenges for insulation, said Troy Coleman, VP and GM of TI’s Power Switches.

TI is looking to transform the heavy coils of the cable windings in transformers and the tightly wound cylindrical coils and mechanical switches of the relays into components that can fit inside a standard IC package while maintaining safety.

TI launched in 2020 a proprietary integrated transformer technology that brings high-density isolated DC-DC power conversion in one package, replacing transformers, one of the pillars in the world of insulation, used for safety purposes and to maintain transients and harmonics under control. To help reduce the cost of electric vehicles, TI is integrating the technology into more of its highly reliable automotive power supplies.

Solid State Relays are the latest in TI’s growing range of ICs for signal and power isolation in automobiles. The company claimed to be the first in a solid-state relay family that will include industrial-grade devices.

High voltage surge protection is critical in industrial grade power supplies, such as solar grid inverters and other renewable energy inverters, as well as robotics and motor control systems. It is important to eliminate disruptive ground loops in power rails with large ground potential differences (GPDs). Data retention during common mode transients and secure isolation of high-side devices are also priorities.

Reinforced insulation

The TPSI3050-Q1 is TI’s automotive grade switching driver with reinforced isolation that can be coupled with a single DC power switch or two back-to-back AC power switches to create a complete solid state relay. TI said the chip integrates power and signal transfer through a single “isolation barrier” that separates the low-voltage side from the high-voltage side (the battery side) of the power rail to better protect against spikes. high voltage.

The built-in 10V gate power supply voltage means you don’t need an isolated secondary power bias. The TPSI3050-Q1 can also act as an isolated dc-dc power supply providing 50mW to auxiliary ICs.

TI said that the highlights of the TPSI3050-Q1 are robustness and reliability. Reinforced insulation offers up to 5 kVRMS of protection. According to TI, the switch driver, which can handle a stiff temperature range of -40 to 125 ° C, has 10 times longer life in a smaller package than electromechanical relays, which can break due to constant use. . The chip fits inside a 7.50 × 5.85mm SOIC package.

For safety reasons, many industry standards require parts with “basic” insulation, which TI believes offers a single layer of insulation against bumps and other hazards in cars. But this means that if the isolation barrier is breached, any additional protection disappears. For “reinforced” insulation, components must be capable of demonstrating electrical resistance, reliability and impact protection equal to twice the basic insulation rating.

The high level of integration in the chip moves at least three components, reducing the footprint by up to 90% by integrating the functions of an isolated power supply, a digital isolator and a gate driver in a single chip.

The new solid state relays can disconnect and connect loads across a single isolation barrier in a fraction of the time of electromechanical relays, enabling safer operation of automotive high voltage systems.

With built-in gate-drive voltage of 10V with peak source and draw current of 1.5 / 3.0A, TI said its customers can pair it with a wide range of external power switches in systems such as on-board chargers.

50% discount on insulation

The TPSI2140-Q1 is a 1400V, 50mA isolated switch that also integrates power and signal transmission into a single chip, saving up to 50% space compared to other non-mechanical devices called photorelays.

The basic insulation protection is 3.75 kVRMS, giving it 4 times longer life against dielectric breakdown than alternatives. The chip tolerates up to 2 mA of avalanche current, 3 times more than existing solutions to enhance security and slow down degradation. It also offers you the TPSI2140T-Q1, equipped with its Thermal Avalanche Protection (TAP) function, which can contain avalanche currents up to 5 mA, adding further robustness.

TI stated that the component, housed in a 10.3 × 7.5mm SOIC package with wide pins for better thermal dissipation, runs on a primary side power current of 7.5mA in the “on” state and 6 μA in the “off” state.

TI is introducing a wide range of other protection features with the TPSI2140-Q1, which uses the company’s capacitive isolation technology to protect against high voltage spikes in electric cars. The semiconductor giant said the switch withstands a voltage spike, also called V.IOSM—Up to 6,000V. In addition, it has an estimated useful life of over 25 years at high voltages of 1,000VRMS.

TI said it is ideal for battery management systems at the heart of electric vehicles to detect failures in the insulation that surrounds high-voltage batteries faster and more reliably than optoelectronic-based photorelays.

The TPSI3050- and TPSI2140-Q1 are in pre-production. Pricing is $ 1.99 and $ 2.75 for 1,000-unit quantities, respectively.

Read other articles in the Power Management series: Power Density Insight

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