Accurate hybrid/electric battery monitor includes isolated interface
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 is fully specified for operation from -40 to 125°C. It 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.
Along with the LTC6804, Linear Technology is introducing 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 1 MHz, 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.
Availability and Pricing
The LTC6804 is offered in a small 8 mm x 12 mm surface mount device. Priced at $10.95 each in 1,000-piece quantities.
The LTC6804 will be available in production quantities in January 2013. The LTC6820 is offered in an MSOP and QFN package and is priced at $2.29 each in 1,000-piece quantities.
More information about the LTC6820 isoSPI transceiver at
www.linear.com/product/LTC6820
More information about the LTC6804 battery monitor at
www.linear.com/product/ LTC6804
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