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BQ40Z50-R1: Unable to activate CHG or DSG FETs when I do not have a fuse

Tejaswi Gode
Prodigy 20 points
Part Number: BQ40Z50-R1
Other Parts Discussed in Thread: BQSTUDIO

Hi,

I'm using the BQ40z50-R1 BMS chip for a project. I redesigned the chip application based on the EVM module. I made some changes mainly to save on component cost and space on a small PCB. 

One of the biggest changes was that I removed the entire FUSE circuit. Basically the FUSE PIN is not connected to anything. Also, made changes to account for a 2S battery pack. When I'm testing, the CHG and DSG registers are always inactive (i.e. 0). See below for a image of my bit registers from the bqstudio app.

Before connecting to a battery pack, and in order to current limit in case of failure, I'm using a power supply with a resistor divider for the 1P sense line. I'm assuming that it has something to do with the FUSE pins, but I could be wrong. I'm in FULL ACCESS mode. 

When I tried to send 001D with 44 command on the Advanced SMD, I did not see any change. 001D is to disable FUSE according to the reference manual. 

My question is what should I do on the firmware and hardware side to ignore the FUSE pin altogether. Should I pull down the FUSE pin?

Thanks,

Gode

  • 0
    TI__Mastermind 34775 points
    Hi Gode, Yes when the FUSE pin is unused as in your we recommend connecting it to VSS. The gauge check the FUSE pin to see if the fuse is blown by the secondary protector, which you don't have in your schematic. Leaving if floating the gauge thinks there's a permanent failure condition. You will have to send PF_CLEAR and disable PF before you can modify the DF.
  • 0 in reply to Damian Lewis
    Prodigy 20 points

    Hi Damien,

    Is there any way to fix this in the firmware, or do I have to tie the FUSE pin to VSS?

    What do you mean by send PF_CLEAR before you can edit DF? I sent PF_CLEAR and then tried to send the 1D00 command using advanced SMB, still nothing changed. 

    Thanks,

    Gode

  • 0 in reply to Tejaswi Gode
    TI__Mastermind 34775 points

    Hi Gode,

    You have to tie the FUSE pin to VSS. I'm not sure it can be fixed in the DF, but you can try setting bit 6 (2LVL) and bit 3 (FUSE) in the Settings>> Permanent Fail Fuse C registers to "0." 

    Another option might be disabling PF_EN and FUSE_EN in the Mfg Status Init register.

    You will have disable PF using cmd 0x24 then clear PF using cmd 0x29 before you can make any update to the Data Flash (DF), if a PF occurred.

    For more details refer to bq40z50 TRM.