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Original question:

BQ76905: OCD1 threshold program

BQ76905: program FET_ENABLE and there is no output

Beida Song
Intellectual 780 points
Part Number: BQ76905
Other Parts Discussed in Thread: BQSTUDIO

Tool/software:

Hi Expert,

When light load, BQ76905 can work normally. After increase to heavy load, customer found that enable FET_ENABLE failed. They increase the Overcurrent in discharge 1 protection threshold/Overcurrent in discharge 2 protection threshold/Short Circuit in discharge protection threshold, and can't recover to work. The Satety Alert A, B is 0x00, ALARM_RAW_STATUS = 0x0c03, BATTERY_STATUS=0x84C0.

  • 0
    TI__Mastermind 25750 points

    Hi Beida,

    Could you provide some more details? In what way is the FET_ENABLE command failing? What is the load for the light load and heavy load? What are the register settings?

    Regards,

    Max Verboncoeur

  • 0 in reply to Max Verboncoeur
    TI__Intellectual 780 points

    Hi Maxwell,

    Customer configure registers as below, other register is set default value.

    1. 0x9038 = 30; 0x903a = 30;

    2. 0x903c = 0x03;

    3. 0x0022 = 1; 

    Output load current is 3A, after Vbat decrease to 11V, enable FET and it will closed autonomously. 

    Customer aims to enable FET to output 10A current, what's the right configuration for registers?

  • 0 in reply to Beida Song
    TI__Mastermind 25750 points

    Hi Beida,

    Is this on the EVM or their own board?

    If it's on the EVM, could they get a screen shot of the registers in BQStudio to see if there are any faults being reported by the device?

    If it's on their board, what is their sense resistor value?

    Regards,

    Max Verboncoeur

  • 0 in reply to Max Verboncoeur
    TI__Intellectual 780 points

    Hi Maxwell,

    It's tested on the EVM.

    Customer aims to enable FET to discharge load and disable FET to stop discharge. The max current is 40A. Could you give a recommendation of registers mapping? 

  • 0 in reply to Beida Song
    TI__Mastermind 25750 points

    Hi Beida,

    I have a few recommendations for settings to change.

    First, Since the max current is 40A, they should change the Curr Gain and CC1 Gain to 196. The default value of 241 makes it so that the device can only measure a maximum of ~32A through the 1mOhm sense resistor. By changing the gain to 196, the LSB (a.k.a. userA) will change from ~1mA to ~1.223mA.

    Next, the current protections would need to be changed. 40A through the 1mOhm sense resistor is 40mV, so the OCD protection should be increased to match. Overcurrent in Discharge 1 Protection Threshold = 21 will set the protection to trigger at ~42A, which affords them a little overhead on their expected current.

    Lastly, the SCD protection needs to also be increased. They should set Short Circuit in Discharge Protection Threshold = 3 or more so that it triggers at a voltage greater than 40mV.

    Regards,

    Max Verboncoeur

  • 0 in reply to Max Verboncoeur
    TI__Intellectual 780 points

    Hi Maxwell,

    Thanks for your update. After rewrite above register value, it doesn't work for customer. Could you share me the whole registers configuration file example? I don't know if the requirement is easy to finish for you. Because I will test these parameters with our EVM and BQStudio. If you can share the file, I can verify it efficiently in our lab.

  • 0 in reply to Beida Song
    TI__Mastermind 25750 points

    Hi Beida,

    Can you elaborate on what failed and how?

    Are faults being reported by the device? Can you share details on their setup and how they are testing?

    The settings I explained should allow 40A of discharge current without the device triggering an OCD or SCD fault.

    Regards,

    Max Verboncoeur

  • 0 in reply to Max Verboncoeur
    TI__Intellectual 780 points

    Hi Maxwell,

    Share with you setup: The input is 5 capacitors connected in series. Total voltage is 13V. Load is electrical load and keep CC=10A.

    Pls review below detailed setup and fault description. Though I set higher protection threshold, which cover 10A, the fault happens and registers changed to default value. Could you give a solution?

    BQ76905 issue-2025-3-3.pdf

  • 0 in reply to Beida Song
    TI__Mastermind 25750 points

    Hi Beida,

    It looks like the EVM was reset. Could you capture a waveform of the BAT pin while testing this? I'm curious if the load is pulling the supply voltage down enough to POR the part.

    Regards,

    Max Verboncoeur

  • 0 in reply to Max Verboncoeur
    TI__Intellectual 780 points

    Hi Maxwell,

    Indeed, the supply is pull down to gnd nearly. How to solve the issue by configuring related registers?

    Blue: output current;

    Pink: supply voltage

  • 0 in reply to Beida Song
    TI__Mastermind 25750 points

    Hi Beida,

    This is basically a short circuit of the battery. The load is pulling more current than the battery can supply, so the battery voltage crashes. All batteries behave in a similar manner under a load that exceeds their supply current.

    The SCD protection of our part should turn off the FETs to prevent this from happening for too long, however it seems that this is occurring at a current much lower than the customer expects.

    There isn't a setting to change to increase the current at which this behavior happens, this is a limitation of the battery itself.

    Regards,

    Max Verboncoeur

  • +1 in reply to Max Verboncoeur
    TI__Intellectual 780 points

    Hi Maxwell,

    The device is broken and it work again after customer use another EVM.