I'm trying to use an integrated chip for Qi Charging + lipo management + overcharge protection and all the hard stuff basically.

The only one that is 'integrated enough' seems to be: http://www.ti.com/lit/ds/symlink/bq51051b.pdf

In the 'Typical Application' circuit there is no system load, and i can't figure out where it's supposed to go from the rest of the spec either.

Am i supposed to connect the load in parallel to the battery? How is that going to protect the battery in any way?

enter image description here

  • \$\begingroup\$ Your load feed is from the battery. \$\endgroup\$ – Andy aka Sep 17 '15 at 14:54

The bq51051b is a wireless battery charging solution, so its only really meant to charge batteries, if you wanted to though, I see no issue with just hooking up your load in parallel with the battery while its connected

System diagram

This image is from section 9.1 of the datasheet.

Please note that this IC doesn't have any over/under-charge protection. You'll need either another IC, circuit, or a battery that has the technology included. This chip does, however, have over-current protection on the charge path. You'll need to properly calculate the the resistor on the ILIM pin in order for this to work. The formulas are in the datasheet.

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  • \$\begingroup\$ that's what i expected, but i don't understand how over-discharge protection works then. probably with another IC? But even then how can the charging controller know the current charge of the lipo when the system load is interfering? \$\endgroup\$ – user65665 Sep 17 '15 at 15:01
  • \$\begingroup\$ Many batteries have over-discharge protection in them, but some don't so you have to make sure, if not then another IC will be in order. The bq5105 chip doesn't detect the batteries charging capability, you program it with the resistor on pin ILIM. \$\endgroup\$ – Funkyguy Sep 17 '15 at 15:04
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    \$\begingroup\$ Over and under discharge are not part of the BQ51051B, you will need another IC and two transistors in common drain configuration. Those IC and transistors are usually part of a battery pack, however, one can find bare cells without any protection, so be careful. \$\endgroup\$ – Lior Bilia Sep 17 '15 at 16:18
  • \$\begingroup\$ @LiorBilia That is a solid clarification, I'll edit my answer. There is a huge difference between overcurrent protection and over/under-discharge protection. \$\endgroup\$ – Funkyguy Sep 17 '15 at 16:51
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    \$\begingroup\$ You have to specifically ask for a bare cell. Most countries do not allow selling such cells, and they are very difficult to transport. Any battery sold to integrators or end consumers must have this protection, otherwise bad things happen. \$\endgroup\$ – Lior Bilia Sep 18 '15 at 16:26

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