My apologies if this is really obvious or if it has been answered before - I did search extensively and didn’t find anything though.
I have a Telit GSM module and am designing a circuit for it where it is powered by a Li-Ion battery. I want to use the Telit’s internal battery charging hardware to charge said battery.
I’ve read the Telit Hardware User Guides and the Telit Battery Charger Application Note many many times but am stumped on one detail.
I don’t know what voltage to supply to the CHARGE pin. (or amperage for that matter)
Is it dependent on the battery, hence Telit do not specify any sure numbers?
The Battery Charger Application note states that they recommend 400mA to keep temperatures under control. They also state that the charger circuit will accept up to 1A. It specifically says that if the voltage is 5.2v, the current of 1A can be accepted.
There’s a chart outlining calculation of loss, which uses 700mA in the example even though this figure is not mentioned anywhere else. This also uses 5.2v in the example.
It’s all got my head in a spin. I don’t know the maximum values the CHARGE pin can accept. Will it take 12v? 8v? 6v? Does it have to be 5.2v exactly? Can it be less than 5 but more than the battery?
The AC adapter I have and want to use is 4.4v and 1.1A
Does anyone know if I can use this directly? Should I put a diode in there to skim off a few hundred mA to bring it under 1000mA?
If anyone can help me out I’d very much appreciate it. I can’t find an example or someone’s previous project anywhere to base mine from. No-one else has published anything I can find about using the Telit module’s internal charger.
cmetom:
I’ve read the Telit Hardware User Guides and the Telit Battery Charger Application Note many many times but am stumped on one detail.
I don’t want people to do the legwork for me, I’m really just looking for what someone else has done in my situation and how it worked out for them. In my months of scouring the web I haven’t found a direct example of someone using the Telit internal battery charging feature.
While talking to a friend of mine tonight, we decided that my 4.4v @ 1.1A charger will be OK, but due to Telit’s recommendation in the Charger App Note of keeping it under 1000mA to minimise heat generation I may have to test this for my application and be prepared to modify.
you have probably already solved the issue but maybe somebody else can be interested in the solution also.
Regarding the LiPol battery conncetion to Telit GSM Module and its charging it is important to don´t focuse on the voltage too much! There is needed to solve the issue of the maximum current going to CHARGE input.
You need to supply the CHARGE imput using a current source or current limiter. Then the voltage on the CHARGE input will change automaticly according the current going into the module.
I have designed a circuit that will alow to charge the LiPol battery connected to module with the current max 200mA. It can be designed in more simple way of course but in case we only have 5V as an input voltage then there is needed to have very small volatge drop on the limiter…you will find the schematic here: http://files.hwkitchen.com/200000145-d6 … ematic.pdf
You can adjust the circuit easily for different current if you like…
