I am working with the MAX17320 and I am looking at two MAX17320 example circuits from AD - the MAX17320 Eval Board and the MAXREFDES1299 for inspiration. Each schematic is roughly the same, except the Eval Board uses more of the features of the chip, as on would expect. I am using Li-ion batteries.

My question involves on part of the schematic of the Eval Board, which is not on the 1299 board. The MAX17320 has an output called PFAIL, which is described as

Permanent Failure Indicator. Connect to a three terminal fuse to take action in case of primary FET failure detection. If not used, connect to GND with a 1kΩ resistor.

In the Eval board, the PFAIL circuit has a transistor connected to a fuse to disconnect the battery in the case of a failure: enter image description here

But the 1299 does not have such a circuit. PFAIL is just tied to ground through a resistor.

My question: in what situations is it wise to include the PFAIL circuit and in what situations is it overkill?

I am new to battery/BMS etc design, so I am trying to learn from examples.


BTW, the connections off the top of the schematic I included go to parts that are not included on the Eval Board. They go to pads that the Eval Board user can use to replace Q1/Q2 with their own transistors.

  • \$\begingroup\$ do a good old risk analysis (FMECA). Do the risks of not having a fuse outweight the risks of having the fuse -> put one. I am almost certain that, given you're asking the questions here, the answer is going to be that you should add the fuse. \$\endgroup\$
    – mlx11
    Apr 15 at 20:55

1 Answer 1


You want such a feature whenever you think there is a risk of damage if too much energy goes into the system (Fire, violent venting, explosion etc.) The alternative is a standard fuse or PTC. It is a standard requirement for certifications such as UL.

  • 1
    \$\begingroup\$ When you say "Too much energy into the system", do you mean when the batteries are being charged? I have a fuse in the load circuit to prevent too much current being drawn from the batteries, but I am guessing this fuse is not the same. \$\endgroup\$ Apr 15 at 18:47

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