Can i charge an Lithium - Ion 14.6 battery with solarpanel with 17.3V using BQ24650 ?

Yes.  Simply modify the bq24650 datasheet's typical application circuit (or EVM circuit) for your panel's maximum power point voltage and maximum power output current.  Your panel's maximum output current is less than 1 A but your battery can take up to 3A charge current. So, your battery charge time will be long.     

Thank you very much Jeff. I just ordered an Evaluation board to try this out.

I see in the documentation (EVM) that MPPSET is set to 17.8 Vdc which is the same value as my panel so that should be ok right ? Regarding maximum power output current i see that in the EVM it is set to be 2A. Should i change R6 so that i get an output of 0.8A as the panel or ? I am aware that the charging will take long time. I calculated that 8h of perfect sun with this panel will produce 6.4h so it will be fully charged. Am i correct ? Should i not also change R13 on the board to set the charge voltage ? Both R13 and R6 are SMD components or ar there a way to hook up to those pins somewhere else and leaving those components intact ?

/mihai

Jeff, can you please verify this :

2.1V * (1+(R13/100k))=16.8v where R13 will be 700k resistor (i made a mistake here in the first calculation, it should have said 700k)

40mV/R6 = 800mA where R6 will be 0.05 ohm resistor

Do you believe that i will run into problems with my charge voltage ? I read somewhere an thread written by you where you said that the Vin from solarpanel must be charge voltage + 0.5V which in my case would be 16.8V+0.5V=17.3V and the solarpanel can deliver 17.8V. I mean it's very close to what the panel can deliver. Would this effect the performance of the charging besides that i only have 800mA ?

In this application note http://focus.ti.com/analog/docs/litabsmultiplefilelist.tsp?literatureNumber=slua565&docCategoryId=1&familyId=411 i see that you give an example where you change Lower Recharge Voltage Threshold. Is this needed in my case with the Lithium - Ion battery ?

/mihai

R13 and R6 were calculated correctly.  I suggest increasing R13 by a factor of 10-100 so you will not waste power through the feedback resistors.

The charger needs some headroom (~0.5V) from its input voltage to the battery voltage in order to continue switching.  If Vin drops or after the battery is close to regulation, the charger stops swithcing at 600kHz will enter 99.9% linear mode, tying its input voltage to the battery.

You do not need to lower the recharge voltage threshold.

Jeff i am not sure i follow you here so excuse me for my question. If i increase R13 by a factor 50 then i will have an resistance of 700ohm * 50 = 35k and that will lover the charge voltage extremely low. What am i misunderstanding ?

I guess i answered my question myself because the R13 should preferably be 700k which i guess should be ok.

I am althoug unsure how to fix the 0.05 ohm resistor, that is not something you find or ?

Sorry for the newbie questions.

You will increase both R13 and R15 by the same amount.

You will purchase a 0.05 ohm resistor from an electronics component distributor and replace the 0.02 resistor on the EVM with the 0.05 ohm resistor using a soldering iron.

thanx Jeff,

Got my EVM today. Great day. :)

Jeff: what happens if i do not change R6 ? I mean it's set to 2A and the panel cannot deliver that under any circumstances so is it needed that i change R6 ?

The input voltage MPPT loop will activate and scale down the charge current when the solar panel voltage starts to droop.

Interesting so that means that the MPPT loop will start earlier because the panel cannot deliver that. Understood correct ? So it is indeed important to change it to what the panel can produce.

Actually, no.  The converter will first attempt to provide the higher charge current but when the input voltage drops below the voltage set on the MPPT pin, the charger will then scale down the charge current to the point where the input voltage rises above the MPPT set voltage.  So, during constant current charging, you could actually leave the charge current setting higher than what you need because the MPPT loop will be in the control.   However, it would be best to resize the current setting resistor for your battery's maximum charge current for two reasons:  1.  protection in the unlikely event the solar panel provides more current than expected and so the charger attempts to charge at a higher than recommended current and 2. the termination current is also a function of that resistor and will likely be set too high for your particular batter.

Thank you for clarifying that. My Max Charge Current with my battery is 3000mA meaning that the setup of 2A is ok to protect the battery in case the current rises.