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bq20z65 Problem with FETs opening/closing

Dylan Temples
Intellectual 270 points
Other Parts Discussed in Thread: BQ20Z65, BQ40Z50, BQ24735

hello,

I'm going to try and be as specific as possible to avoid some of the misunderstandings I have seen in other questions regarding FETs. Please correct me on any misunderstandings I may have about the operation of the FETs with this eval board.

When discharging or charging batteries (ie, when conducting, when current is flowing through the circuit), the FETs must be closed.

After reaching the max/min voltage programmed in the dataflash, the FETs should open to stop current from moving through circuit. This action should be automatic based on the programming on the chip and the operation of the bq board.

Currently, our FETs can only be controlled manually by using a reset command in bqeasy. Our PRES register is set, and we have no PF registers set.

In addition, once the batteries have been fully discharged (the FD bit in battery status is set), the FETs should open to stop current from leaving the battery. Currently, the FETs are remaining closed, even after the FD bit in battery status is set.

 

Only by sending the board the default dataflash image can we get the FETs to open, then when we want to close them (to start conducting) we send it a 0x41 word (reset).

Does anyone know why this might be happening and how we can fix it?

 

Thanks!

 

  • 0
    TI__Guru* 76230 points

    If you are using a smart charger, when you have a the FC or FD bits set, the guage broadcasts this message to the smart charger and it stops charging. If you aren't using a smart charger, then you will have to use the CUV and COV thresholds to turn off the FETs.

     

    To manually turn on the fets you write SMB command 46 word 0006. To turn off, write SMB command 46 Word 0000

    -Onyx

  • 0 in reply to Onyx Ahiakwo
    Intellectual 270 points

    Thanks for your quick reply.

    We're right there with you in terms of charging. During a test charge our smart battery charger shut off the current when the board broadcast that it no longer needed charge.

    Our problem now lies in DISCHARGING. Even when the FD bit is set the smart battery charger does not stop draining current. Do you know why this might be and how we can fix it?

     Just to be clear, we are using a smart battery charger and in application we will not be able to send manual commands to the FETs to cease draining current from the batteries.

    Thanks

    Kat

  • 0 in reply to Dylan Temples
    TI__Guru* 76230 points

    Also the bq20z65 can turn the charge fet off when fully charged if the chgfet bit flag is set in the operation cfg B of the data flash. with regards to the discharge issue, check that your CPE, HPE (if host uses PEC ) and Bcast bits are set in your data flash in cfg B

    -Onyx

  • 0 in reply to Onyx Ahiakwo
    Intellectual 360 points
    I am working on an embedded Linux project with the i.mx5. I am using version 2.6.31.14 of the Kernel. I2C works fine and I can see various sensors from the board on bus #1. I can remove the power cord and the battery keeps the board running. The issue is i am not able to charge the battery as a smart battery.

    I am using BQ24735 Charger & BQ40z50 Fuel gauge, the battery is charging when it is connected to motherboard running with Linux. (switch ON case). I am following below steps to charge after booting up linux.

    1) Writing charge current (1024mA) and charge voltage (16000mv) to charger. (I2C Address - 0x12)

    2) Monitoring the Battery using Fuel gauge (I2C Address - 0x16)

    3) Updating the Charging voltage and current manually for each 2 seconds.

    4) Getting and Displaying Percentage.

    Problems :

    1) Wrong percentage Showing.

    2) When it comes to < 30%, Whole System getting Switch OFF. After that when i switched ON means, again Percentage starting from 30%.

    3) Charging percentage is going up to 103 or 104%.

    4) If i want to charge the battery in OFF condition, means its not charging. After Enabling BCAST Bit also, there is no change in Charging Voltage and Charging current, It is not updating so its not charging.

    5) If i enabled CPE Bit with BCAST bit means, the Voltage alone changing to 10469mv and Charge Current is 0A.

    6) After complete charge of battery, If i put idle (OFF) without working also, charge is fully leaking from the battery. Each Battery Voltage is reaches upto 1.8V (Max Cell Voltage is 4.2V)

    7) Is there any chance to enable the SBS Configuration register from Code, (Register Address) Instead of using windows application. ?

    So please Suggest me, how to solve this above problems, how can i make charger to smart charger. and How to charge the Battery in OFF condition using Fuel gauge (Update Charge Current and Charge Voltage)