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BQ24650: BQ24650 charging problem

shraga Leitner
Intellectual 630 points
Part Number: BQ24650

Finally the board is working and charging the battery.

the problem now is that charging current is very low, is about 40 to 80 ma.

how I can control the charging current so it at list it will be 500ma to 1A?

Shraga

  • 0
    TI__Guru**** 158961 points
    Shraga,

    The sense resistor between the SRP and SRN pins set the maximum charge current. Is the resistor divider at MPPSET properly sized for the solar panel's MPP in order to be maximum power from the panel? What is the panel's VOC and ISC? Are you charging 1-,2- or 3- cell LiIon battery? What is the voltage at the charger's MPPSET pin? It is possible that the charger is pulling maximum power from the panel, but that is not enough to provide the current that you want.
  • 0 in reply to Jeff F
    Intellectual 630 points

    We did check and it works like the evaluation board

    When the battery was low we get around 600ma charge current 

    We would like to know how we can increase the charge current let's say up to 1.5 A

    Thank you in advance

    Shraga

  • 0 in reply to shraga Leitner
    TI__Guru**** 158961 points
    Shraga,

    When you say it works like the evaluation board, do you mean you have the same components as the evaluation board? If not, can you send your schematic? Did you size the components using the design spreadsheet at www.ti.com/.../sluc175.

    I need more information in order to help. What is the panel's VOC and ISC? What is the voltage at MPPSET when you get 600mA charge current?
  • 0 in reply to Jeff F
    Intellectual 630 points

    5126.SCHEMATIC1 _ PAGE1.pdf5126.SCHEMATIC1 _ PAGE1.pdf

    I did check and all the test points the same like in the evaluation board

  • 0 in reply to shraga Leitner
    TI__Mastermind 25800 points
    Hey Shraga,

    Just to re-iterate what Jeff mentioned: We need the details of the input you are attaching to the charger.

    If the MPPT pin is regulating the voltage at the input due to a weak input source, then you likely not see full charger the higher the battery voltage goes. So can you provide more details about the input power and battery connected?


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Intellectual 630 points

    The input power is from a regular power supply 24V 

    the battery is a car battery 12v 100 amp

    we would like to know how we can control the charging current  - increase it up to 2A 

    Shraga

  • 0 in reply to shraga Leitner
    Intellectual 630 points

    dear

    we have the same problem with TI evaluation board - bq24650EVM

    please let me know how we can change the charging current 

    Shraga

  • 0 in reply to shraga Leitner
    TI__Mastermind 25800 points
    Hey Shraga,

    Pleas measure the voltage at the following pins:
    VFB
    SRN
    TERM_EN
    MPPSET


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Intellectual 630 points
    Hello Joel

    VIN=28V
    VOUT= 12.54
    TS=INTERANL
    VFB=2.09
    SRN=12.54
    TERM_EN=0
    MPPSET=1.86

    regards
    Shraga
  • 0 in reply to shraga Leitner
    TI__Mastermind 25800 points
    Hey Shraga,

    Based on that data, your battery voltage as seen by the charger at the SRN pin is very close if not exact the same as your resistor programmed battery regulation voltage 12.58V. This means charger is very deep in the CV (Constant Voltage) mode of charging. At this point, the current is only dictated by the voltage difference between 12.54V at SRN and the actual cell voltage divided by the line impedance between the charger and cell.

    Normally, the charger would terminate if the current went as low as you reported. However, because EN_TERM is low here, the charger has disabled termination and will continue to charge deep in CV mode. This is interesting because in your schematic, there is a zero Ohm connecting EN_TERM to VREF. I would verify why this is not the case .


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Intellectual 630 points

    good morning

    1. I would like to mention that we are also testing your evaluation board and we get the same value 

    2. I would like to ask if I can control the charging current?

    3. what would be happened if we take OFF the EN_TERM?

    thank you in advace

    Shraga.

  • 0 in reply to shraga Leitner
    TI__Mastermind 25800 points
    Hey Shraga,

    1) Was anything modifed on our EVM in order to be used with your battery? What are the jumper configurations when using our EVM, specifically JP3? Also note that the regulation voltage programmed on the EVM through the resistor divider is the same as that on your board. So the test setup is likely same and the charger is in Constant Voltage mode of charging. This means you cannot control the charge current. Only the delta voltage between the cell and charger and line resistance will dictate this current.

    2) Charge current can only be programmed by changing the RSNS resistor between SRN and SRP.

    3) When EN_TERM is pulled low, termination is disabled meaning when the charger is deep in CV phase of charging, it will not stop charging if the charge current gets to low. If EN_TERM is pull high, terminate is enabled meaning the charger will stop charging. Please review the Li-ion charge profile for a better understanding of this. Refer to Figure 9. Typical Charging Profile in the datasheet.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Intellectual 630 points

    dear Joel

    What is the value of RSNS if we would like to charge up to 2A the battery

    on the Evaluation board is 0.02 

    how we can calculate this resistor value?

    Shraga

  • 0 in reply to shraga Leitner
    TI__Mastermind 25800 points
    Hey Shraga,

    The charger current setting can be programmed by referring to Section 8.3.3 Battery Current Regulation of the datasheet.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Intellectual 630 points

    dear Joel8.3.3 Battery Current Regulation

    Battery current is sensed by resistor RSR connected between SRP and SRN. The full-scale differential voltage
    between SRP and SRN is fixed at 40 mV. Thus, for a 20-mΩ sense resistor, the charging current is 2 A. For
    charging current, refer to Equation 3:

    The charging current max 640 MA and i cant get 2A like in the datasheet

    please let me how to increase to 2A

    Shraga.

  • 0 in reply to Joel Hernandez II
    Intellectual 630 points

    Dear Joel.

    As I said before we did check with TI evaluation board and we get the same results.

    Acutely our board is a copy of TI evaluation board so I don’t see how the datasheet said 2 A and we get only 600 ma max.

    The power comes from the power supply so we don’t have a current problem

    Please let us know what to do how we can increase the charging current and reach at list 1.5A pic

    why we can get simple answers about how we can increase the output current?


    Shraga

  • 0 in reply to shraga Leitner
    TI__Mastermind 25800 points
    Hey Shraga,

    As I mentioned before, I believe your battery voltage is too high. Can you try with a lower voltage battery and test please? Based on a previous response, VBAT (as measured on VSRN) was 12.54V. This is the programmed regulation voltage of the charger. Current will dictated by the voltage different between the actual battery cell and the charger's VSRN pin, divided by any line impedance.


    Regards,
    Joel H