I am planning on using a Diodes Inc. AP9211 battery protection circuit for an IoT project, and I have a question regarding usage.

The AP9211 will be embedded in the PCB, while the battery will be inserted afterwards. Once the battery is inserted, I do not expect to change it long-term. My schematic for the battery protection follows the datasheet guidelines, except I connect P- (the PACK- shown in the datasheet) to GND directly, as this is the GND of the whole circuit.

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Since this IC is intented to be used in the battery pack and not separate, do you see any issues with connecting P- directly to GND? I would think not, because even if I placed the AP9211 on the battery pack, I would then connect P- to my circuit's GND through a cable or connector of some sort.


1 Answer 1


There is no problem initially connecting P- to BATT- as this IC needs to short those two terminals to begin operating if there is no charger connected. From Page 2 in the Notes:

For power down mode, when first connecting AP9211 system board to the battery, it is necessary to use charger or to short P- to the battery negative polarity. Once the AP9211 is activated, the charger or connection can be removed, otherwise the battery cannot discharge current through system board.

Edit: You should connect BATT-, VSS and S1 to your circuit GND. It is my understanding that you can leave P-unconnected and floating if you do not use the charger side of the circuit and the protection side will still operate as per your use case but you should still check that yourself to confirm.

  • \$\begingroup\$ Hi, thanks for the response. However, wouldn't connecting VSS, BATT- and S1 to my circuit's GND bypass the protection? As far as I understand, P- should connect to my circuit's GND, that way when the protection activates, my circuit's GND is disconnected from BATT- via the MOSFETs. \$\endgroup\$ May 29, 2021 at 3:31
  • \$\begingroup\$ I may have misunderstood your question. Do you intend to use a charger to recharge your battery ? \$\endgroup\$ May 29, 2021 at 4:43
  • \$\begingroup\$ Yes, the battery will connect through the protection to a battery charger. Specifically, the BQ24074. So my question was mainly: since the AP9211 will be located on my PCB and the battery will be inserted afterwards, is it OK to connect the P- node of the AP9211 shown in the datasheet to my circuit's GND. I think it should be fine, but I was double checking. \$\endgroup\$ May 29, 2021 at 15:24
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    \$\begingroup\$ It looks to be fine to me too from the battery pack typical application circuit for the BQ24074. However the initial state logic should be checked to make sure the AP9211 IC doesn't hold the circuit in overcurrent mode, from this question which you may have already seen. \$\endgroup\$ May 30, 2021 at 2:18

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