Linear Technology's 0.04%-accurate hybrid/electric battery monitor includes isolated interface

Linear Technology has announced the LTC6804 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 3^rd-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 m of cable using only twisted pair. Two communication options are available: With the LTC6804-1, multiple devices connect in a daisy chain with one host processor connection for all devices. With the LTC6804-2, multiple devices connect in parallel to the host processor with each device individually addressed. The LTC6804 minimizes 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. GPIO 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 store serialization and calibration data, enabling modular systems. The LTC6804 surpasses the environmental, reliability, and safety demands of automotive and industrial applications. The LTC6804 is fully specified for operation from -40°C 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. "The LTC6804 combines 30 years of analog experience with hard-earned lessons in automotive battery management," says Mike Kultgen, design manager for Linear Technology. "On the bench, or on the road, this part delivers outstanding performance." Along with the LTC6804, Linear Technology is introducing the LTC6820 isoSPI transceiver. The LTC6820 enables bidirectional transmission of the SPI (Serial Peripheral Interface) bus 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. The LTC6804 is offered in a small 8- x 12-mm surface mount package. Priced at $10.95 each in 1,000-piece quantities, samples, demonstration boards and the data sheet are available now. The LTC6804 will be available in production quantities in January 2013. The LTC6820 is offered in an MSOP and tiny QFN package and is priced at $2.29 each in 1,000-piece quantities. Samples, demonstration boards and the data sheet are available now. Summary of Features: LTC6804 & LTC6820 LTC6804

• Measures up to 12 battery cells in series
• Stackable architecture supports 100s of cells
• Built-in isoSPI interface
  • 1-MB isolated serial communications
  • Uses a single twisted pair, up to 100 m
  • Low EMI susceptibility and emissions
• 1.2-mV (max) total measurement error
• 290 μs to measure all cells in a system
• Synchronized voltage and current measurement
• Delta-sigma converter with built-in noise filter
• Engineered for ISO26262-Compliant Systems
• Passive cell balancing with programmable timer
• 5 GPIO or analog inputs
  • Temperature or other sensor inputs
  • Configurable for I²C interface
• 4-?A sleep-mode supply current
• 48-lead SSOP package

• 1-Mbps isolated SPI data communications
• Simple galvanic isolation using standard transformers
• Bidirectional interface over a single twisted pair
• Supports cable lengths up to 100 m
• Very low EMI susceptibility and emissions
• Configurable for high noise immunity or low power
• Requires no software changes in most systems
• Ultralow, 2?A idle current
• Automatic wake-up detection
• Operating temperature range: -40° to 125 °C
• 2.7 to 5.5 V power supply
• Interfaces to all logic from 1.7 to 5.5 V
• Available in 16-lead QFN and MSOP packages