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BQ24450: BQ24450 Full Charge Issue

Teach Me
Expert 1940 points
Part Number: BQ24450

Hi TI Experts,

I conduct a study with BQ24450EVM-691 but I fail to fully charge it.

It maintains at 11.65V and 2 days continuously from 11V.

Vin supply: 12V

Battery Charge: 12V Lead acid 7Ah

Below are the parameters i use:

VTH : 10.5V

VFLOAT: 13.8V
VBOOST: 14.7V

Ipre: 10mA

trickle charge rate: 10mA

charge rate set: 400mA

Rc: 46.4kohm

Rt: 30ohm

Rp: 619 ohm

Rd: 590kohm

Rb: 17.4kohm

Ra: 215kohm

Risns: 0.619ohm

Please do advice is there anything wrong?

Any suggestion on this?

Thanks,

Br,

Teach Me

  • 0
    TI__Mastermind 21590 points

    Hi,

    The minimum Vce of the drive transistor is about 2 typical. Try increasing the the input voltage to about 14 to give more headroom and check to see if you still have this issue.

     

    Regards,

    Raheem

  • 0 in reply to Raheem
    Expert 1940 points
    Hi Raheem,

    I unable to adjust the Vin as the supply is fixed at 12V.
    Is there any way that can make the battery to full charge to 12V.

    Thanks,
    Br,
    Teach Me
  • 0 in reply to Teach Me
    TI__Mastermind 21590 points
    Hi,
    The charger needs a certain amount of headroom. If this requirement isnt met, the battery wont be charged to its full voltage.
    Regards,
    Raheem
  • 0 in reply to Raheem
    Expert 1940 points

    Hi Raheem,

    I have redo the setting for the BQ24450 with higher input voltage of 15.57V so that it is able to have a dropout of 2V.

    At the first few days of testing, it charged up to around 13.7V and it maintain at the voltage of 14.8V (Vboost) for 5 days and it seems like it is not dropping down to Vfloat of 13.8V that I set.
    I worry that if the lifetime of the battery will be shorten if it is charged with this high voltage continuously. 
    Hope to get your reply soon for this issue.
    Here also I attached my new calculation for your references.  

     
     
    Thanks,
    Br,
    Teach Me
    Our customer have concern on the component that appeared to be “darker” or “discolored”, please see attached image. Part details as below:-
     
    Part Number: 6164010S791S-218
    Part Description: TR MODULE DC-DC 1-OUT 0.8V TO 3.6V 2A 8-PIN USIP
     
    Referring to the datasheet, the maximum peak soldering reflow temperature is 260degC, the specification is the same as Plexus reflow specification.
     
     
    Hence, we need your help to get Texas Instrument advice for enquires below,
     
    1) Is the “discolored” component OK to use?
    2) What cause this problem?
    3) Will this affect the functionality of component and cause any reliability issue?
  • 0 in reply to Teach Me
    TI__Mastermind 21590 points
    Hi,
    What is the status of the STAT1 and STAT2 pins when the IC should be in float mode?
    Regards,
    Raheem
  • 0 in reply to Raheem
    Expert 1940 points

    Hi Raheem,

    Just to verify, is the Hi-Z stat is done by disconnecting the resistors from the relevant pins? 

    Also, I used the calculated resistors and connect them according to the schematic diagram on EVM, supposingly it will change the charging mode accordingly isn't it?

    I am using the BQ24450EVM. There is already default resistor value on the STAT1 and STAT2 pin.

    Any changes need to be done?

    Please advice.

    Thanks,

    Teach me