build a charger with LT3652

Discussion in 'The Projects Forum' started by david1234, Dec 17, 2014.

  1. david1234

    Thread Starter Member

    Nov 27, 2013
    81
    1
    I want to use this IC , so I will be able charge the battery while using my device .
    and when I disconnect the charger the device will continue working and not reset\start over.

    http://cds.linear.com/docs/en/datasheet/3652fd.pdf

    this is the battery I'm using (can't change it):
    LiPO battery
    nominal :11.1V
    Max Charge Volt:12.8

    the charger I have is 12.6V 2A

    now I have some questions :
    1. I understand that PIn7 (V_FB) is the voltage to the battery,right?
    so I need to change to value of the resistors to work on 11.1V
    2. the NTC (pin8) - do I have to connect it to the battery ? or I can leave it not connected to nothing ? in the battery I do have a NTC wire. is it impotent?
    3. I want to use the CHRG (pin4) so I will know when the battery is full ? so just to connect LED with 10K to it?


    if there is a simpler\easy and ready solution for my needs - I will be more then happy to hear,

    Thanks ,
     
    Last edited: Dec 17, 2014
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,963
    743
    1, the resistor value i would suggest is to replace the 542K to 1.2 or 1.3Meg, this will give a charge of 12.2V.

    2, the Ntc is important as this detects overheating of the battery.
     
    Last edited: Dec 17, 2014
  3. david1234

    Thread Starter Member

    Nov 27, 2013
    81
    1
    first of of thank .
    but if i change the 542k to 1.3M I get
    ~2.7V

    show me what I do wrong -
    Vin=12.5V (this is the charger Voltage)
    Vin*459k/(459k+1.3M)
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,963
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    The Vfb pin has a fixed 3.3V ref internal setting, so adjust the resistors to give your desired output charge.
     
  5. david1234

    Thread Starter Member

    Nov 27, 2013
    81
    1
    sorry , but i don't understand your calculation
    can you show me how you got this R=1.2-1.3M ?
    Vin is 12.6V-this is the charger I have now for the battery
    Thanks ,
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,963
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    if you want 12.6v, then the resistor is 12.6 - 3.3= 9.3v / (3.3v/459k) = 1.29Meg.


    read the datasheet!!
     
  7. david1234

    Thread Starter Member

    Nov 27, 2013
    81
    1
    maybe me English is not so good - so I didn't understand
    just to be clear - some more questions :
    1. I have a 220AC-12.6DC charger that charge the battery now , I'm still going to use it .
    when I change the resistor to 1.3M resistor it will charge the battery with ~12.6V - right?
    and if I change the external charger to 15V - will it still charge the battery with 12.6V?

    2.The diode between Boost and BAT is a normal 0.7V diode , not something special ?

    is this all the changes I have to do in the circuit in order to make it work?

    Thanks for your help :),
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,963
    743
    Your english is ok, if you want to charge the battery at 12.6v, the input voltage must be a minimum of 3.3V higher, thats 15.9V input, if you use a 15V input, then you can only charge the battery at 11.7V.

    As long as you input a voltage of 16V or higher the battery will only charge at the value set by the resistors.
     
  9. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,281
    1,228
    VIN (Pin 1): Charger Input Supply. VIN operating range
    is 4.95V to 32V. VIN must be 3.3V greater than the programmed
    output battery float voltage
    (VBAT(FLT)) for reliable
    start-up. (VIN – VBAT(FLT)) ≥ 0.75V is the minimum
    operating voltage, provided (VBOOST – VSW) ≥ 2V. IVIN ~

    85μA after charge termination

    This pin wants 3.3 volts when the battery is fully charged -- in your case 12.6 volts (4.2v for each cell) for the battery and 3.3 volts at the fb pin.

    Lithium batteries like to catch on fire. this is to prevent them from doing that.
    Yes


    if there is a simpler\easy and ready solution for my needs - I will be more then happy to hear,

    Easy way:

    http://www.ebay.com/sch/i.html?_fro...o+charger&_nkw=lipo+charger+balancer&_sacat=0
     
  10. hufanae

    New Member

    Mar 18, 2011
    1
    0
    I suggest use pots for initial designs, so that you have a good window range when setting the sweet voltage spot [i.e. 1 meg 2 meg.. 500K ohm pots, prefer same footprint size i.e. 805 or 1206 smt's] (I suggest use try to set these common resistor value or resistors that are readily available in stock that have good ppm (<50ppm) and good tolerance 0.01% or 0.1% ); so use pots to tweek in the voltages. NTC are cheap. buy the 10k with b3380. place it where battery gets hot, unless you want to blow up. :)
     
  11. david1234

    Thread Starter Member

    Nov 27, 2013
    81
    1
    ronv - thanks for all the details,
    now I understand I can't use my correct charger , and if i want to work with this IC I need to get a 15V 2A power supply .
    this is a problem from me now - (time issue)
    I want to know something else -
    if I connect the my system to the battery to the charger :
    טעינה במקביל.png

    can I do this?
    I have taken an empty battery and connect it like shown in the image .
    after a half an hour - I see that the battery can hold the project (without the charger of course....)

    so can I leave it like this?
    or maybe connect some small circuit from transistors that will disconnect the charge of the battery or something?

    (sorry for the change of the topic , but it's work in progress)

    Thanks ,
     
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