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TPS61089 Boost converter for battery charging?

Ville Savolainen
Prodigy 110 points
Other Parts Discussed in Thread: TPS61089

I was thinking if I could use the tps61089 boost converter to create a charging voltage of 8.4V for 2 x li-ion cells in serial, and use the current limit feature to control the maximum current delivered to batteries. This way I could create a charge current from USB power 5V, and with the current limit and voltage regulation, there would be no need for a dedicated charging controller. I could use an MSP430 uC to cut off charging when charge current at the voltage regulation level 8.4V will decrease to predetermined value, and control the balancing. Does this sound feasible, or its there something I am not aware now which would make this impossible?

  • 0
    TI__Mastermind 40080 points

    Hi,

    What is the maximum current delivered to the batteries? Because the minimum current limit value (or minimum peak switch current value ) of TPS61089 is >2A.

    And could you please draw a simplified block diagram for your application?

    BR,

    Helen

  • 0 in reply to Helen chen
    Prodigy 110 points

    Batteries can take charge up to 3A, and as far as I understood the minimum peak switch current value is not the same as the output current value, and not even the same as the average input current value. The DC input would be able to deliver 3A, and I would like to see a charging current for batteries to be somewhere between 1-2.5A.  I did a quick diagram to show my idea.  So there would be the DC input to boost converter, connected to batteries which are in series. The MSP430 would sense the voltage of batteries and turn off the boost converter when batteries are fully charged, or if either of batteries get over voltage and also control the bleed circuits to discharge one of the batteries if they are not in balance. I forgot from diagram the current sense input for MSP430, to see how much current is flowing between boost converter and batteries. (li-ion charge to finish when at voltage regulation mode the current drops to certain value)

  • 0 in reply to Ville Savolainen
    Prodigy 110 points

    Ordered the evaluation module for tps61089 and tried it - it works! :) Just adjusted the current limit with a resistor to a lower level and it is possible to use it as a battery charger. The currency decreases somewhat as the voltage rises during charge, but generally it is working just fine! :) 

  • 0 in reply to Ville Savolainen
    TI__Mastermind 40080 points

    Thanks for the update, the idea is good.

    one thing confuse me: that is the Boost's input voltage is 5V/3A, but the Boost converter's output is 8.4V/3.8A.  The input adapter can't output such high power. The output is 6-8.4V/1.5A is resonable!!

  • 0 in reply to Helen chen
    Prodigy 110 points

    yes, there was some mistake in the values, in my prototyping I used 1.5A Output and it worked fine, with a 5V 3A charger. And after comparing the input voltage*current to the output voltage*current, I was able to see expected results. Also the TPS61089 module as well as all of the components were very cool to the touch during operation,  so the efficiency was not decreased in this setup and I was pleasantly surprised how efficient the conversion was!

  • 0 in reply to Ville Savolainen
    TI__Mastermind 40080 points

    Good!

    The conversion efficiency is around 93-94% in your application if you choose a good inductor.