Scalable: The best possible use of electrical energy in cars requires efficient battery management.
Scalable: The best possible use of electrical energy in cars requires efficient battery management.
( Source: Texas Instruments)

enhanced range New chips for greater range in hybrid and electric vehicles

| Author / Editor: Michael Eckstein / Florian Richert

Increase the radius of action, reduce CO2 emissions: New battery management ICs from TI and reference designs are to help hybrid and electric vehicles achieve greater range.

Electric and hybrid vehicles are intended to help reduce emissions of harmful (climatic) gases such as CO2. The path to largely energy-independent vehicles leads from micro- and mild hybrid to full-hybrid, plug-in-hybrid and ultimately purely battery-electric vehicles. An efficient battery management system (BMS) is essential if these vehicles are to make the best possible use of electrical energy. Texas Instruments (TI) has now created a complete package of new analogue ICs and certified reference designs based on them for battery management and traction inverter systems. The designs help carmakers achieve Automotive Safety Integrity Level D (ASIL D) for their developments, the highest functional safety requirement of the road vehicle standard ISO 26262.

The core of the new reference design is the battery monitor and balancer module BQ79606A-Q1. According to the manufacturer, it is scalable for monitoring circuits from 6 to 96 cells. For 6 cells, therefore, a circuit measuring only 20 mm x 40 mm and based on a BQ79606A-Q1 is required. The design implements battery monitoring in a daisy-chain configuration to provide a high-precision and reliable system design for 3 to 378 series-connected lithium-ion battery packs with voltages from 12 V to 1.5 kV. Up to 64 cells can be integrated into the daisy chain, for which TI has developed its own protocol.

Ring connection for additional functionality

Optionally, a ring connection of the components used is also possible. "Although this is not required for ASIL-D certification, it represents an additional safety function," says Karl-Heinz Steinmetz, General Manager Automotive Systems, HEV/EV & Powertrain at TI. This means that all interlinked components can be addressed even in the event of a cable break and can, therefore, continue to be used. This could be clearly located and a warning signal could be displayed on the dashboard. In addition, the vehicle could drive even further, for example to the nearest workshop. Without this ring connection, however, the vehicle would have to switch to a safe system state according to ASIL D, which usually means standstill.

"In order for a vehicle to make optimum use of the energy stored in the battery, it is necessary to precisely determine the upper and lower capacity limits," says Steinmetz. TI has therefore designed the BQ79606A-Q1 so that it can monitor temperature and voltage values very precisely. This helps to maximise the radius of action and protect the battery from overcharging, which benefits its service life.

"In addition, the BQ79606A-Q1 battery monitor ensures reliable status transmission," explains Steinmetz. This, in turn, supports system designers in complying with safety requirements up to ASIL D. In order to meet the ASIL D requirements, the module is designed to be fully redundant internally. According to TI, external sensors can be connected via 6 ADC inputs for temperature measurements, for example. "Ultimately, safety, i.e. functional safety, is always a system issue," says Steinmetz. "And it's the manufacturer's responsibility."

Reliable heat management in the entire traction inverter system

Drive systems of electric vehicles have to cope with high currents. Traction inverters and batteries often work with outputs of several kilowatts. This can cause components to heat up considerably and the high temperatures are potentially harmful to the costly and sensitive elements of the powertrain. Sophisticated thermal management of the system is therefore crucial not only for the performance of the vehicle but also for the protection of its occupants.

To protect powertrain systems such as a 48 V starter generator from overheating, TI has developed the TMP235-Q1 precision temperature sensor with analogue output. It has been available since mid-March 2019 and is part of the reference design now presented.

According to the manufacturer, the device consumes little power, only 9 µA in sleep mode. Its accuracy is typically ±0.5 °C or a maximum of ±2.5 °C over the full temperature range from -40 °C to +150 °C. "This helps traction inverter systems react to temperature jumps and apply the right temperature management techniques," says Steinmetz.

Advanced, space-saving protection for traction inverter systems

Together with the recently introduced UCC21710-Q1 and UCC21732-Q1 gate drivers, the temperature sensor is designed to help developers realize smaller and more efficient traction inverter designs. According to TI, the devices are the first isolated gate drivers with integrated sensor functions for IGBTs (Insulated-Gate Bipolar Transistors) and FETs based on SiC (Silicon Carbide). TI offers the driver modules in two variants: One with an integrated FET (Miller Clamp), one with an external FET ¬-developer has more degrees of freedom to place the switching elements close to the power stages.

"With our new gate drivers, system reliability can be increased in applications with operating voltages of up to 1.5 kVRMS," explains Steinmetz. They insulate against voltage peaks of up to 12.8 kV and are designed for a rated insulation voltage of 5.7 kV. In addition, the components would score points with short response times: "They protect against overcurrent events and at the same time ensure a safe shutdown of the system.

With another new reference design, TI makes it possible to supply the new gate drivers directly from the 12 V vehicle electrical system. It masters three types of bias supply options for IGBTs and SiC-FETs for the power stages of traction inverters. According to Steinmetz, the design consists of reverse polarity protection circuits, clamping circuits for electrical transients and over-voltage and under-voltage protection circuits. The compact design also includes the new LM5180-Q1, a 65V flyback converter for primary control that includes an integrated 100V/1.5A MOSFET.

This article was first published in German by Elektrotechnik.