Accurate hybrid/electric battery monitor includes isolated interface

November 01, 2012 // By Paul Buckley
Linear Technology has introduced a high voltage battery monitor for hybrid electric and electric vehicles, and other high voltage, stacked-battery systems.

An LTC6804 can measure up to 12 series connected battery cells at voltages up to 4.2 V with 16 bit resolution and better than 0.04% accuracy.  This high precision is maintained over time, temperature and operating conditions by a sub-surface Zener voltage reference similar to references used in precision instrumentation.  When stacked in series, the LTC6804 enables the measurement of every battery cell voltage in large high voltage systems.  Six operating modes are available to optimize update rate, resolution and the low pass response of the built-in 3rd order noise filter.  In the fastest mode, all cells can be measured within 290 µsec.    

Multiple LTC6804s can be interconnected over long distances and operated simultaneously, using Linear Technology’s proprietary 2-wire isoSPI interface.  Integrated into every LTC6804, the isoSPI interface provides high RF noise immunity up to 1 Mbps and up to 100 meters of cable, using only twisted pair.  Two communication options are available: with the LTC6804-1, multiple devices are connected in a daisy chain with one host processor connection for all devices; with the

LTC6804-2, multiple devices are connected in parallel to the host processor with each device individually addressed.

The LTC6804 was designed to minimize power consumption, especially during long-term storage where battery drain is unacceptable.  In sleep mode, the LTC6804 draws less than 4 µA from the batteries. General purpose I/O pins are available to monitor analog signals, such as current and temperature, and can be captured simultaneously with the cell voltage measurements.  Additional features include passive balancing for each cell with a programmable balancing timer for up to 2 hours, even when the LTC6804 is in sleep mode.  The LTC6804 interfaces with external I2C devices such as temperature sensors, ADCs, DACs and EEPROM.  Local EEPROM can be used to store serialization and calibration data, enabling modular systems.

The LTC6804 was designed to surpass the environmental, reliability and safety demands of automotive and industrial applications.   The LTC6804