Protecting your battery isn’t as hard as you think

bq77905 3S to 5S Advanced Stackable Low Power Battery Protector EVM

When it comes to any type of protection, the solution should be simple. Protection should be something that you design and set up once and don’t have to worry about again; at least that’s how it should be. But when it comes to more and better battery protection, designers may worry about what this might cost them going forward.

Given that battery protection circuitry usually sits inside the battery pack out of sight and isn’t typically considered a cool, sleek new application feature, the design engineer may not give it much thought. But as we’ve learned from recent events, battery-protection can cause major headlines if not done properly.

In general, for any protection device you want the setup to be simple: an IC that protects your system but does not come with a huge “price tag” in terms of high current consumption. Here is where TI’s bq77905 family of battery protectors for three- to five-series cells and beyond help by providing the protection your system needs with the lowest power drain.

In battery applications you always need to have a primary protector that will serve as the first line of defense and any protection after will have the role of secondary protection. Secondary protection, to briefly mention, allows for last resort type of battery protection which is usually simple over-voltage protection. To learn more about battery protection you can visit my blog, Get to know your battery pack: Part 1.

The bq77905 is a great primary protector for applications such as power tools; garden tools; vacuums; and robotic applications like drones, robotic vacuums and robotic lawnmowers. These types of industrial consumer applications take a toll on their battery packs, since consumers want their power tool or robotic vacuum to immediately perform as if it were AC-powered. Typical current consumptions for these applications can go as high as 50A (power tools) and as low (but still high) as 15A continuous current (vacuums). In addition to supporting high current draws, the internal battery pack circuitry needs to consume ultra-low power for longer battery lifetimes and overall runtime.That is where the bq77905’s 6µA of average current consumption really comes in handy.

Industrial consumer applications typically include battery-pack sizes of 3S (small power tools or drones), 4S (drones), 5S (professional power tools), 6S (industrial drones), 7S (vacuums), 10S (garden tools or larger power tools like saws) and even 20S. To accommodate these various sizes, creating a common platform for battery-pack design eliminates the engineering costs associated with redesign and unfamiliarity between different IC architectures. The bq77905 also offers the capability of stacking to provide cell count flexibility to your design.

In general, protection should be straightforward, easy to use and should not cost much (power consumption, price, safety). In addition, you want your protection devices to provide flexibility for your design to allow scalable approaches for various cell counts, which help in overall design cost. Protection should never limit what the application can do.

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  • So this chip protects Lithium batteries - not necessarily the load. OK, but does it protect the battery against reverse insertion? Is that part of the overcurrent discharge function?

  • Hi Otto,

    It depends on what you mean by reverse insertion. Technically this device would protect against reverse insertion, but the rest of the battery would need to be designed to protect against what happens after the protector trips.

    Thanks

    Miguel