The LTC6802 battery-monitoring IC

A winner of the Product of the Year award for 2008, the LTC6802 multicell, precision battery-monitoring IC from Linear Technology was designed with the help of several groups in the company. The voltage-reference group at LTC led by Erik Soule, vice president of signal conditioning products, Jim Douglass, and Mike Kultgen, was given the task of designing the battery-monitoring product, and they recognized early in the design process that they would need access to the talent from across the company. For example, they knew the product would need the help of the converter group because the chip would use up to 60 V, work and maintain accuracy in a hot, noisy automotive environment, handle up to 4-kV ESD, and have a low-power shutdown mode. The team also wanted it to sense a 3-V differential on top of 300 V of a common-mode voltage within just a few millivolts of accuracy.

The LTC6802 design team

The first challenge they had to confront was the isolation on the current-mode serial interface. Next, they had to figure out how to get an A/D converter to handle 60V common-mode voltage.

They went to every group to get ideas, and it was an applications engineer that came up with the idea they eventually used. After nailing down the topology for handling the high voltage, they had to decide how to pull together all the different blocks.

They pulled circuit blocks from every business unit in the company. They had to determine how to embed the reference in an ASIC and make it work with high voltage.

Embedding caused packaging problems because the die can be corrupted by high voltage in the plastic of the package. So it needed special shielding and coding techniques. That led to the challenge of how to measure the battery voltage that’s on top of 300 V, and then how to get the data back to a microprocessor with a voltage at chassis ground level.

They also had to figure out how to communicate the data that’s floating at a high voltage and how to get it to the microprocessor without adding digital isolators or optocouplers, since they take a lot of power and add cost.

The design solved some very difficult design challenges that took about four years for the groups from Texas, Colorado, and California to complete..

Paul O’Shea