Able to read out and report the condition of each of the batteries in vehicular battery systems with output buses of 1000 V and greater, Linear Technology’s LTC6803 stacks up (literally) to meet the needs of these new and expensive power reservoirs.
Chip companies continue to innovate in the automotive space, particularly when it comes to power. Linear Technology and Diodes Inc. are leading the field with best-in-class ICs.
Better Battery Stacks
In our recent interview, Linear Technology cofounder Bob Swanson pointed out that the automotive market was key for the company (see “As Linear Technology Turns 30, Electronic Design Interviews Cofounder Bob Swanson” at www.electronicdesign.com). He also noted that hybrid and electric cars require some very sophisticated battery stack monitoring chips, a challenge that the engineers at Linear decided to tackle.
He then discussed Linear’s ability to stay ahead of the competition by developing a better IC once the competition catches up. This company philosophy is embodied in Linear’s LTC6803 EV battery monitoring chip (see the figure).
This second-generation chip is based on Linear’s LTC6802, which was released in 2008. The LTC6803 has the same pinout and price of the previous version but boasts additional features that evolved from 24 months of dealing with the auto industry, specifically from working with the industry on a new automotive standard, ISO 26262.
The LTC6803, like the earlier LTC6802, is intended to be designed into battery packs (see “High-Voltage Electric/Hybrid Vehicle Battery Monitor Chip Evolves” at www.electronicdesign.com). Each chip can monitor up to 12 individual battery cells in series. The input channels on both chips can handle common-mode voltages up to 60 V, and both offer a stackable architecture, plus built-in FETs that allow overcharged cells to be discharged.
But the really special feature is the serial bus, which can be daisy-chained to provide full reporting on the entire battery bank via a single port. The precision of those measurements is guaranteed to be 0.25% or better, and guaranteed maximum measurement time for all cells in the system is 13 ms. Another standard feature is an on-chip temperature sensor
The LTC6803 also adds a wider cell measurement range (0.3 to 5 V) to support nickel-metal-hydride (NiMH) batteries and supercapacitors in addition to lithium chemistries. Unlike the LTC6802, the power input of the LTC6803 is isolated from the stack, enabling the chip 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.
SBRs for Automotive Apps
The other winner in the automotive category is a family of Super Barrier Rectifiers (SBRs) designed for automotive use from Diodes Inc. The company acquired SBR technology in late 2006, with the focus on expanding its existing core customer base in the consumer and computing markets, and is now expanding into the automotive market.
The patented technology integrates two existing rectifier technologies into a single device via a state-of-the-art integrated circuit wafer processing technology. The technology was designed with some key objectives, including low VF, a high reverse avalanche rating, and low reverse leakage.
The SBRs released earlier this year include the SBR20A60CTBQ, SBR30A45CTBQ, and SBR3045CTBQ, which handle output currents of 20 A and 30 A and are provided in an industry-standard TO-263 package. All are AECQ101 qualified. A fourth device, the SBR1045D1Q, is rated for 10 A and comes in the slightly smaller TO-252 package.
The low VF (0.48 V for the SBR1045D1Q) means circuit power efficiency can be significantly improved and much cooler operation achieved, increasing reliability. Reliability is further increased by the devices’ higher reverse avalanche rating of more than twice that of an equivalent Schottky diode. This provides greater protection against transient voltage spikes. Finally, the lower reverse leakage at high temperatures provides a higher safe operating area (SOA) and guards against thermal runaway in high-temperature operating conditions.