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BQ40Z50-R1: Second Level Protection

Bobby B
Prodigy 70 points
Part Number: BQ40Z50-R1

The BQ40Z50-R1 datasheet lists a set of Primary (1st-level) Safety Features and a list of Secondary (2nd level) Safety Features.  The simplified schematic as well as the reference schematic on the EVM both include a second level protector.

Is the second level protector a necessary component or just an additional feature?  What functionality and/or safety features are lost if the BQ40Z50-R1 was used without the second level protector?  Would the BQ40Z50R1 alone still provide over/under voltage protection? cell balancing?

Appreciate any information you can provide.  Thanks!

  • 0
    Expert 2475 points
    The bq40z50-R1 is a full featured gauge that offers 1st level protection features that disable the FETs and 2nd level protection features that can blow the fuse and disable the pack. The purpose of the Secondary protector is to add additional protection if the bq40z50-R1 were to become damaged. As you know, over voltage conditions can cause a catastrophic failure event for Lithium cells. The Secondary protector will blow the fuse if the cell voltages transition higher than the over voltage protection thresholds in the gauge. The Secondary protector is not required for some packs. I have found them used in most applications where consumer safety could be at risk should the pack fail, such as electronic devices that are carried onto an airplane.