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Renesas Unveils 14-Cell Li-ion BMIC for EVs/HEVs

The battery-management chip offers ±2-mV accuracy across automotive temperature ranges, while maximizing driving time and range.

Renesas Electronics’ fourth-generation lithium-ion (Li-ion) battery-management IC (BMIC)—the ISL78714—features all of the functions expected of a critical systems component, such as battery-pack monitoring accuracy, temperature monitoring, fast data acquisition, and fault checking.

The new IC also provides cell balancing and system diagnostics to protect 14-cell Li-ion battery packs with ±2-mV accuracy across automotive temperature ranges. Thus, system designers can make informed decisions based on absolute voltage levels, while also maximizing driving time and range for all EV variants, such as HEVs, PHEVs, and BEVs.

The IC incorporates a 14-bit analog-to-digital converter (ADC) and associated data-acquisition circuitry. The device also offers up to six external temperature inputs (two available from GPIOs) and includes fault detection and diagnostics for all key internal functions.

The ISL78714 meets the stringent reliability and performance requirements of battery-pack systems, with safety features enabling automotive manufacturers to achieve the ISO 26262 automotive safety integrity level (ASIL D). In addition, the ISL78714 monitors and reads back over/undervoltage, temperature, open wire conditions, and fault status for 112 cells in less than 10 ms, or 70 cells in 6.5 ms.

Three cell-balancing modes are included: Manual Balance mode, Timed Balance mode, and Auto Balance mode. Auto Balance mode terminates balancing after a host-specified amount of charge is removed from every cell.

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Shown is a typical application for the ISL78714 battery-management IC.

Multiple ISL78714s can be connected together via a proprietary daisy chain that supports systems up to 420 cells (30 ICs) (see figure). It provides transient and EMC/EMI immunity said to exceed automotive requirements. The ISL78714s daisy-chain architecture uses low-cost capacitive or transformer isolation, or a combination of both, with twisted-pair wiring to stack multiple battery packs together while protecting against hot-plug and high-voltage transients. A watchdog timer automatically shuts down a daisy-chained IC if communications is lost with the master MCU.

Among other features are:

• A two-wire daisy-chain communications system using capacitor or transformer coupling up to 1 Mb/s

• Fully differential cell input range of ±5 V accommodates fuel-cell and bus-bar measurement requirements for aging battery packs

• 15-year board-level accuracy (long term drift) of ±6 mV @ ±6 σ

• High diagnostic coverage for cell voltage and temperature measurements

• AEC-Q100 Grade-2 qualified and specified for operation from −40 to +105°C                                                                                                                           

Renesas developed the IC in partnership with the Formula E team Mahindra Racing, helping them win on the racetrack. The partners designed and integrated a low-voltage Li-ion battery-management system featured in Mahindra Racing’s electric race cars.

“Together, we designed and integrated a low-voltage Li-ion battery-management system featuring ISL78714 ICs and RH850 microcontrollers in Mahindra Racing electric race cars,” said Niall Lyne, Senior Director of Product Marketing and Applications, Automotive Mixed-Signal/Power and Video, Renesas Electronics.

A battery-management system (BMS) reference design is available, which includes five ISL78714 ICs and a RH850/P1M MCU to form a complete 70-cell evaluation platform for external balancing. The reference design kit provides setup and data logging via CAN and UART. Also provided is a GUI, Altium layout files, and low-level drivers for the RH850 peripherals and ISL78714. Hardware, software, and interface reference manuals are included, along with an EMC report. The reference design kit facilitates the ability of electric-vehicle system designers to port their software to the RH850 MCU, scale to any battery pack size, and save development time (up to one year according to Renesas).

Mass-production quantities of the ISL78714 Li-ion battery management IC are available now in a 64-lead TQFP package.

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