High voltage battery stack monitor enhances HEV/EV battery management systems

February 22, 2011 // By Paul Buckley
Linear Technology has introduced a second generation high voltage battery monitor for hybrid/electric vehicle (HEVs), electric vehicles (EVs) and other high voltage, high performance battery systems. The LTC6803 is a complete battery measuring IC that includes a 12-bit ADC, a precision voltage reference, a high voltage input multiplexer and a serial interface.

Each LTC6803 can measure up to 12 individual battery cells in series. The device’s proprietary design enables multiple LTC6803s to be stacked in series without optocouplers or isolators, permitting precision voltage monitoring of every cell in long strings of series-connected batteries. The LTC6803 follows the road-proven LTC6802, introduced in September 2008 with the same functionality and pinout, plus a number of performance enhancements.

The maximum total measurement error of the LTC6803 is guaranteed to be less than 0.25% from -40 to 125°C. The LTC6803 offers an extended cell measurement range from -300 mV to 5 V, enabling the LTC6803 to monitor a wide range of battery chemistries, as well as supercapacitors. Each cell is monitored for undervoltage and overvoltage conditions, and an associated MOSFET is available to discharge overcharged cells. Added functionality is provided by an onboard 5V regulator, temperature sensor, GPIO lines and thermistor inputs.

For long-term battery pack storage, the current consumed by the integrated BMS can potentially unbalance the cells. The LTC6803 addresses this concern with a standby mode that draws less than 12 µA. Furthermore, the power input of the LTC6803 is isolated from the stack, allowing the LTC6803 to draw current from an independent source. When powering from this input, the current draw on the pack is reduced to less than 1 µA.

The LTC6803 is designed to surpass the environmental, reliability and safety demands of automotive and industrial applications. The device is fully specified for operation from -40 to 125°C. The device 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 meet this standard, the LTC6803 includes a redundant voltage reference, extensive logic test circuitry, open wire detection capability and a watchdog timer for fail-safe designs. The LTC6803 is designed to withstand up to 75 V, providing more than 20% of overvoltage margin for a full string of 12