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I'm designing a wearable device, which is powered by a lipo battery. It can consume up to 100 mA, with 2A short peaks. The battery needs 360mA for charging. Charging IC with power path is used.

And it is meant to be charged with a standard USB (micro-B or C). It will be a kind of mass-product device, that will be used by lots of people in unpredictable environments and with unknown USB power sources. In any case, it is supposed to be safe and stable.

Do I need to detect port abilities for current limiting? For example with special USB interfacing ICs, like PTN5150A or FUSB303, MAX14637? Or can I just limit the input current on my charger IC to 0.9A/0.5A (USB 3.0/2.0 mode)? What is the best solution here? I don't want to blow up somebody's USB adapter, but I don't want to over-engineer the whole system too.

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Do I need to detect port abilities for current limiting?

You need to tell the charger you need > 150 mA, like any good device would.

That takes a single resistor!

For example with special USB interfacing ICs, like PTN5150A or FUSB303, MAX14637?

You'll want one of these, no matter what:

Or can I just limit the input current on my charger IC to 0.9A/0.5A (USB 3.0/2.0 mode)?

Detecting that will require some logic glue anyways.

Realistically, 360 mA charging current is very little, so I doubt you'll be able to blow up anything with that.

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  • \$\begingroup\$ Thanks for your answer! Could you please explain about resistor? Is it about usb-c ? \$\endgroup\$ Jul 14 at 10:19
  • \$\begingroup\$ But total current consumption during charging would be 460 mA with 2A peaks. \$\endgroup\$ Jul 14 at 10:32
  • \$\begingroup\$ you can't do 2A peaks without communicating that you'll need that. A lot of chargers and USB hosts will just detect a fault if you suddenly do that, and shut down. The resistor I was referring to is simply 200Ω between D+ and D-, and identifies the USB port as simple charger-only dedicated charging port, without any data transport facilities. If you need data transport, you'll need dedicated USB controller hardware, anyway, so this becomes a different problem. (nothing of this has to do with USB-C specifically, I think that DCP standard dates back to ca. 2000) \$\endgroup\$ Jul 14 at 10:39
  • \$\begingroup\$ Would it work for both of micro-B and type-C ? \$\endgroup\$ Jul 14 at 11:02
  • \$\begingroup\$ I think so. You just don't want to have to charging plugs on the same device: that literally helps noone (everyone has enough USB-micro-B cables...) and you need to protect things against people connecting two chargers at the same time, potentially even with different earth potential. So, really, settle on one connector. \$\endgroup\$ Jul 14 at 11:05

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