I'm looking for a little help with a simple battery charging project. I've bought a pack of cheap USB charging boards on ebay (link) with the intent of using one to charge a small Li-Ion battery. While testing it, I've noticed that the board is running pretty hot. Within 30 seconds of plugging it into a USB wall adapter (5V,1A output), the charging board heats up to ~140F/60C (according to my multimeter's thermometer probe). The battery, however, stays room temp.

I was pretty concerned about this, but after looking up the spec sheet for the charging IC (TC4056A), I see it lists the maximum junction temperature as 125C (257F). As I understand it, the max "junction temperature" is the component's max operating temperature.

This project is a bit of a learning experience for me, so I'm wondering if this sounds ok. While 140F is well below the chip's junction temp, it just seems really high. Thank you for your help.

  • \$\begingroup\$ Sounds quite normal. \$\endgroup\$
    – winny
    Commented Jun 17, 2018 at 3:32

1 Answer 1


The max Tjcn is 145’C but every 10C rise above 25’C ambient reduces life expectancy 50% approx.

Jcn to case Thermal resistance (Rjc) for a TSSOP8 is Rjc= 60’C/W and Rja=130’C so design with 1A on battery at 3.6V has a 1.4V drop=1.4W .

There is more loss at lower Vbat initially so your operation is (expected) or normal but a better design dissipates heat thru large copper plane thru the TSSOP leads or has a mini alum. Heat Sink bonded to lid.

So your junction temp, Tcjn, rise may be twice the case temp, Tc without these improvements.

It’s your choice. Lots on Amazon may be found.

It’s cheap and so are heatsinks but they shave every penny off costs.

  • \$\begingroup\$ Now I'm not trying to be rude, but a little punctuation would make this response so much easier to read. I'm trying to understand your example/numbers, but I think I'll need to do a little more research on thermal dissipation first (not sure what "Rjc" and "Rja" mean). I can also try to find some tiny heatsinks in the mean time. \$\endgroup\$ Commented Jun 17, 2018 at 15:58
  • \$\begingroup\$ Made necessary changes , thanks in advance for your positive feedback. \$\endgroup\$ Commented Jun 17, 2018 at 17:10
  • \$\begingroup\$ Like Ohms Law with V=I*R, temp rise $$\Delta T=Pd*Rth$$ , for each interface ; junction to case Rjc and case to ambient, Rca = Rja junction to ambient with minimal heat sink. \$\endgroup\$ Commented Jun 17, 2018 at 18:47

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