I have a single-cell Li-Po battery (3.7V 380mAh) connected to a dedicated charge controller (TI bq21040). The programmed charge current is 180mA.

Although the battery is shipped with a PCB with overcurrent/overvoltage/undervoltage protection, I want to add another layer of protection outside by inserting a polyswitch (Bel-fuse 0ZCJ0050FF2G) between the battery and the VBAT terminal of the charge controller.

I am concerned that the serial resistance of the polyswitch (Min.150mΩ, Max.700mΩ after being tripped) might affect the charging process.

Because the programmed charge current is relatively low, the voltage drop caused by the polyswitch will not exceed 0.1V during the CC (fast-charge) phase.

My guess is that the controller might switch from CC mode to trickle charge (voltage-regulated) mode earlier, but the voltage drop will become even lower as the charge current drops, and eventually the effect will be negligible.

Is it a normal practice to protect a Li-Po/Li-ion using a polyswitch in this way? If it is, how can you avoid any negative effects? On what criteria can you choose which polyswitch product to use?

I searched a lot but I could not find anything useful yet and I am freaking out because I am running out of time to validate anything. Thank you in advance.


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