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Electronics => Projects, Designs, and Technical Stuff => Topic started by: ruumoo on November 30, 2018, 10:46:07 am

Title: Usb-C 2s Liion charging Circuit
Post by: ruumoo on November 30, 2018, 10:46:07 am
I'm designing a pcb for a portable aplication. I want to use a 2s liion battery as power and I would like to charge it over usb-c.
This is my current plan of attack:
https://i.imgur.com/jad1JO4.png

I already have a USB-C pd controller, that can deliver the full 100W, aswell as a liion charge controller and the output step downs, which aren't important to the circuit.
Now I just need a fitting step up, step down converter that converts the 5-20V from the usb port to 7.4 V for charging the batteries.

Now for my questions:
1. Is this a viable circuit, or does it have some giant flaw I overlooked?
(Preferably, I don't want to blow up 4 18650 cells)
2. How would I go about limiting charging current? In my current cinfiguration, the batteries could draw the full 100W, if they decide to do so, which would decintigrate my PCB

Gesendet von meinem LG-H930 mit Tapatalk

Title: Re: Usb-C 2s Liion charging Circuit
Post by: jbb on November 30, 2018, 07:01:41 pm
Have a look at the bq25700 range from TI.

Buck boost with:
- input current, voltage limit
- system output voltage *before* charge current measurement (allows proper charging current control even if system load is all over the place)
- fairly accurate charge current limiting
- monitor ADCs
- I2C / SMBus control

With the right MOSFETs, efficiencies > 90% are quite possible.

Does requires chunk of support components, though.
Title: Re: Usb-C 2s Liion charging Circuit
Post by: ruumoo on November 30, 2018, 08:08:16 pm
Quote from: jbb on November 30, 2018, 07:01:41 pm
Have a look at the bq25700 range from TI.

Buck boost with:
- input current, voltage limit
- system output voltage *before* charge current measurement (allows proper charging current control even if system load is all over the place)
- fairly accurate charge current limiting
- monitor ADCs
- I2C / SMBus control

With the right MOSFETs, efficiencies > 90% are quite possible.

Does requires chunk of support components, though.
Sounds promising, but I will have to work through the 84 pages of datasheet first

Gesendet von meinem LG-H930 mit Tapatalk

Title: Re: Usb-C 2s Liion charging Circuit
Post by: jbb on December 01, 2018, 04:10:37 am
Quote from: ruumoo on November 30, 2018, 08:08:16 pm
Sounds promising, but I will have to work through the 84 pages of datasheet first

I know the feeling  :-\