Linear Technology has unveiled the LTC6804 high voltage battery monitor for hybrid electric and electric vehicles, and other high voltage, stacked-battery systems. The device can measure up to 12 series connected battery cells at voltages up to 4.2V with 16 bit resolution and better than 0.04% accuracy. According to Linear 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 optimise 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 290µsec.
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 1Mbps 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 minimise power consumption, especially during long-term storage where battery drain is unacceptable. In sleep mode, it draws less than 4µA from the batteries. General purpose I/O pins are available to monitor analogue 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 meet the environmental, reliability and safety demands of automotive and industrial applications. It is fully specified for operation from -40°C to 125°C and has been engineered for ISO 26262 (ASIL) compliant systems and a full set of self-tests ensure that there are no latent fault conditions. To accomplish this, the LTC6804 includes a redundant voltage reference, extensive logic test circuitry, open wire detection capability, a watchdog timer and packet error checking on the serial interface.
“The LTC6804 combines 30 years of analogue experience with hard-earned lessons in automotive battery management,” says Mike Kultgen, design manager for Linear Technology.
Along with the LTC6804, Linear Technology has also introduced the LTC6820 isoSPI transceiver. The LTC6820 enables bidirectional transmission of the Serial Peripheral Interface bus (SPI) across an isolated barrier up to 100 meters. With the LTC6820, the SPI data is encoded into a differential signal, which is then transmitted via twisted pair and a simple, inexpensive Ethernet transformer. The LTC6820 supports SPI data rates up to 1MHz, using matched source and sink currents to eliminate the need for a transformer center tap and to reduce EMI. The drive currents and the comparator thresholds are set with two resistors, allowing the system to be optimized for cable length and signal-to-noise performance. The LTC6820 is a companion to the LTC6804 high voltage battery monitor with its built-in isoSPI interface. Battery management systems using the LTC6804 can interface to external components, such as microcontrollers, via the LTC6820.