Battery monitoring chip gets better, cheaper successor

November 18, 2015 // By Christoph Hammerschmidt
High-voltage battery stacks in hybrid and battery electric vehicles need to be carefully monitored all the time. For this purpose Linear Technology introduced the LTC6804 monitoring chip three years ago. Now the company has presented a successor to the 6804: The LTC6811 offers the same high current sensing exactness of 0.04 % and a number of additional features. The good news is that the new chip costs 25% less than its predecessor.

Like its predecessor, the LTC6811 uses a deep buried Zener diode as voltage reference. Unlike the current product. the successor has additional filter cutoff frequencies, more sophisticated passive and active balancing control features, new ADC commands and enhanced fault coverage for functional safety. An LTC6811 can measure up to 12 series-connected battery cell voltages. With 8 programmable 3rd order low pass filter settings, the LTC6811 provides high noise reduction. In the fastest ADC mode, all cells can be measured within 290µsec.

For large battery packs, multiple LTC6811s can be interconnected and operated simultaneously, using Linear Technology’s proprietary 2-wire isoSPI interface. This interface provides electrically isolated, RF noise immune communication for data rates up to 1Mbps. Using twisted pair, many LTC6811s can be connected in a daisy chain to one host processor, enabling the measurement of hundreds of cells in high voltage battery stacks. “This communication interface is as robust as CAN but requires significantly less design effort”, explained Bostjan Bitenc, Field Application Engineer at Linear Technology in Munich.

With batteries being a safety relevant vehicle subsystem, they have to meet the ISO 26262 safety standard (ASIL B or higher) along with the monitoring circuitry. The LTC6811 is has been engineered to meet these requirements through extensive fault coverage via its redundant voltage reference, logic test circuitry, cross-channel testing, open wire detection capability, a watchdog timer and packet error checking on the serial interface.

Since the LTC6811 is pin-compatible with the LTC6804, it can be used as a drop-in replacement for existing designs. The device is supported by Linear’s Linduino technology, an Arduino-based microcontroller board and software library. The microcontroller board includes an electrically isolated USB port and directly connects to the LTC6811 demonstration board, providing a simple platform for evaluating and developing the LTC6811.

More information:

Challenges in Battery Management for Hybrid/Electric Vehicles