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BQ24105EVM: BQ24105 3cell LiPo battery charger

Milan Ptacek
Prodigy 50 points
Part Number: BQ24105EVM
Other Parts Discussed in Thread: BQ24105

Dears,
... we planning use this IC BQ24105 chip in our a new product, where we use external backup 3cell LiPo battery pack.
For check a possibility of use this chip "BQ24105" we bought a BQ2105EVM.
When we use it on the default - factory configuration the charginig of one LiPo cell is well.
But after modification for charging 3cell LiPo battery the charging process is poor.

Assembly change:
R5, R7 - original value 200kOhms change to new values

R5 - 187kOhms
R7 - 37.4kOhms

And after this modifications the charger working intermittently no continuously, across charge 1cell battery.
The used battery are 3 pcs LiPo 3.7V/1300mAh connected in serial stack.

I send to You a scope from TP7 point.
scope_1: working continously (1 cell)
scope_2: working intermittently (3cells)
scope_3: zoom from change of charge

Many thanks for Yours reply
Milan

scope_0

scope_1

scope_2

  • 0
    TI__Mastermind 40845 points

    Hello,

    What is your input voltage for this? This is a buck charger, so please make sure your input is above the regulation voltage.

    Can you also send waveforms of the charge current during each operation; also zoomed in waveforms of the switching on TP7?

    Thanks,

    Mike Emanuel

    Please click "Resolved" if this answered your question.

  • 0 in reply to Michael Emanuel35
    Prodigy 50 points

    Hi Emanuel,

    the input voltage is 16VDC, 

    When I try use small Pb Lead Acid Battery 12V - 1.3Ah the charging process is continuously clean, I thing good.

    Also my Idea is, each LiPo battery [LP-503759-1S-3] include inside some protectiv IC, which affecting the process of serial connenected  3 pcs batteries.

    Milan

  • 0 in reply to Milan Ptacek
    TI__Mastermind 24075 points

    Hi Milan,

       Can you take a scope capture of the BAT pin?

  • 0 in reply to Kedar Manishankar
    Prodigy 50 points

    Hi Kedar,

    I send You the two scopes, where is in first case connected 3pcs of LiPo batteries in serial,

    and sigle Pb Lead Acid Battery

    1.blue - Battery voltage

    2.green - Main Power

    3pcs LiPoBatteries are connected in serial wire

    1pc Pb Lead Acid Battery connected

    Thanks with regards

    Milan

  • 0 in reply to Milan Ptacek
    TI__Mastermind 24075 points

    Hi Milan,

       Can you tell me the DC voltage you observe the BAT pin at, as well as your charge regulation voltage setting? Do you have any cell balancing or protection circuitry in place for your series battery LiPo?

  • 0 in reply to Kedar Manishankar
    Prodigy 50 points

    Hi,

    - the voltage of three LiPo in serial connectet (stocked) bateries is 11.93V,

    - no, is not any cell ballancing protection available

    - i thing, that is pressent, see Battery datasheet [R5402N204KD]

    - the charging voltage changed by R5 a R7, see above 

    1666651.pdf

    Milan 

  • 0 in reply to Milan Ptacek
    TI__Mastermind 40845 points

    Dear Milan,

    Your waveform suggests you are continually dipping below the recharge threshold because of too much impedance to the battery. First you fully charge the BAT pin to regulation (12.6 V). Because there is too much impedance, your actual battery voltage could be 12.3 V. This means the BAT pin will also be 12.3 V after the charging is stopped. But because the recharge threshold is 300 mV, once enough leakage lowers the battery voltage, you will start charging again. This will happen repeatedly as the charger keeps trying to fully charge the battery. Please lower the impedance from the BAT pin to the actual battery and see if that improves anything.

    Thanks,

    Mike Emanuel

    Please click "Resolved" if this answered your question.