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BQ76952: Recovery from SCDL by Load detect

Sho Takayama
Intellectual 390 points
Part Number: BQ76952

Tool/software:

I want to recover from Short Circuit Lach Protection.
Please teach me Load detection.

If I read Safety StatusA(0x03) and  Safety StatusC(0x07) and set SCD or SCDL, I send LOAD DETECT_ON(0x009E).

If removed, are SCD and SCDL cleared?
Do I need any other settings?

  • 0
    Intellectual 390 points

    My settings are as below.




  • 0 in reply to Sho Takayama
    TI__Mastermind 42060 points

    Hello Takayama-san,

    We have assigned an engineer to this and he will provide a response by tomorrow Slight smile.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Sho Takayama
    TI__Expert 4320 points

    Hello,

    Load detection is a option that allows the device to recover from Short Circuit in Discharge Latch or Overcurrent in Discharge Latch protection fault when a load is detached from the pack or the system load is higher than ~20kΩ. When load detect is enabled and there is a fault, a current source will be periodically enabled out of the LD pin. If the voltage at the LD pin is less than 4V then a low impedance load is still attached and the fault will not recover. If the voltage at the LD pin is higher than 4V then the load has been removed or there is a high impedance load, and the fault can recover. For more information on how load detects work you can refer to section 5.2.18 Load Detect Functionality of the Technical Reference Manual

    Load detection will only recover the SCDL not SCD. SCD will recover based on Protections:SCD:Recovery Time (section 5.2.6 Short Circuit in Discharge Protection of the Technical Reference Manual)

    You can refer to Table 5-14. Short Circuit in Discharge Protection Operation (continued) of the Technical Reference Manual for options on resetting SDCL.

    Best regards,

    Thomas Rainey

  • 0 in reply to Thomas Rainey
    Intellectual 390 points

    Hello,
    Thank you your reply.

    Load detection is a option that allows the device to recover from Short Circuit in Discharge Latch or Overcurrent in Discharge Latch protection fault.
    Load detection will only recover the SCDL not SCD. 

    Please teach me about noted above.

    For example, in my settings, is the following correct?
    ① DSG-FET turns OFF when an SCD event occurs, and an SCDL event occurs at the same time.
    ② when a load is detached from the pack, SCDL is released.（SCD is not released)
    ③ After SCD-recovery time has elapsed, SCD is released.
    ④ If ② and ③ are achieved, the DSG-FET will be turned on.

    and,
    I send LOAD DETECT_ON(0x009E) when SCD potect event(SafetyStatusA).
    Should I send it when SCDL potect event(SafetyStatusC).


     

  • 0 in reply to Sho Takayama
    TI__Expert 4320 points

    Hello,

    1. You are correct! When a SCD fault is triggered the DSG-FET will turn off (if configured for autonomous FET control). In your settings you have the SCDL limit set to 1, this means that SCDL will trigger when SCD triggers.

    2. You are correct! When a load is detached from the pack or the system load is higher than ~20kΩ SCDL will begin to decrement every Protections:SCDL:Counter Dec Delay interval if no new SCD faults occur. With your settings it would decrement once every 18 seconds.

    3. You are correct! The device will recover from SCD after Protections:SCD:Recovery Time. With your setting would be 16 seconds.

    4. You are correct! If the device is configured for autonomous recovery, then the DSG FET will turn back on when SCDL and SCD faults are cleared.

    Sending LOAD_DETECT_ON() on SCD or SCDL would not matter because with your settings they happen at the same time. 

    Load detect can be autonomously controlled using Protections:Load Detect:Active Time and Protections:Load Detect:Retry Delay. If both are set to 0 then you can manually control them using 0x009E LOAD_DETECT_ON() and 0x009F LOAD_DETECT_OFF() subcommands. For more information on controlling load detect you can refer to section 5.2.18 Load Detect Functionality of the BQ76952 Technical Reference Manual (Rev. B).

    Best regards,

    Thomas Rainey

  • 0 in reply to Thomas Rainey
    Intellectual 390 points

    Hello,

    Thank you your reply.

    I understood.

    I didn't set 0 to Protecttion:Load Detect:Retry Delay,
    so I will set it and check it.

  • 0 in reply to Sho Takayama
    Intellectual 390 points

    Hello,

    It's still not working.

    CHG-FET remains ON, but is Load detect related?

  • 0 in reply to Sho Takayama
    TI__Expert 4320 points

    Hello,

    Do you have CHG FET Protections A[SCD] and CHG FET Protections C[SCDL] enabled? This will enable a SCD and SCDL fault to turn off the CHG FET.

    Can you also try sending the LOAD_DETECT_ON() command after the SCDL fault has trigger?

    Best regards,

    Thomas Rainey

  • 0 in reply to Thomas Rainey
    Intellectual 390 points

    Hello,

    >>Do you have CHG FET Protections A[SCD] and CHG FET Protections C[SCDL] enabled? This will enable a SCD and SCDL fault to turn off the CHG FET.

    No.

    >>Can you also try sending the LOAD_DETECT_ON() command after the SCDL fault has trigger?

    I will try it.

    thank you

  • 0 in reply to Sho Takayama
    Intellectual 390 points

    Hello,

    I send LOAD_DETECTION_ON() after the SCDK fault has trigger,

    but it's still not working.

  • 0 in reply to Sho Takayama
    TI__Expert 4320 points

    Hello,

    If you do not have CHG FET Protections A[SCD] and CHG FET Protections C[SCDL] enabled then the CHG FET will not turn off if there is a fault. So it is logical to see the CHG FET still active when the SCD and SCDL faults occur.

    Are you removing the load from the system or is your load above ~20kΩ?

    Best regards,

    Thomas Rainey

  • 0 in reply to Thomas Rainey
    Intellectual 390 points

    Hello,

    Tnank you your reply.

    I checked the LD voltage(Direct command 0x38) when the load was removed.


    I think the load detection worksd, because LD voltate is 4.0V or more.

    However, the load detection is not works.

  • 0 in reply to Sho Takayama
    TI__Expert 4320 points

    Hello,

    I will test on bench with your settings and let you know the results by tomorrow.

    Best regards,

    Thomas Rainey

  • +1 in reply to Sho Takayama
    TI__Expert 4320 points

    Hello,

    After testing on bench here was the results: 

    If Load Detect: Active Time was not zero and the Load Detect: Retry Delay was zero, the SCDL fault would recover when the LD reached above 4V.

    If Load Detect: Active Time was zero and the Load Detect: Retry Delay was zero, then LOAD_DETECT_ON() was sent the LD pin would read above 4V. However, the SCDL fault would not recover (as you were seeing).

    To manually control the load detect you can set Load Detect: Active Time to zero and the Load Detect: Retry Delay to zero. Then when you send LOAD_DETECT_ON() you can read the LD pin voltage and if it is above 4V you can send SCDL_RECOVER() (recovering the fault manually).

    Best regards,

    Thomas Rainey

  • 0 in reply to Thomas Rainey
    Intellectual 390 points

    Hello,

    Thank you your reply.

    I understood that LOAD_DETECT_ON() command is for HOST to monitor Load PIN, and HOST must detect removal load and send SCDL_RECOVER command to release SCDL.

    What should be the LD PIN threshold for HOST to detect removal Load?
    3V or 4V?

  • 0 in reply to Sho Takayama
    TI__Mastermind 42060 points

    Hello Takayama-san,

    This is up to you, you decide what voltage your host wants to send the SCDL_RECOVER() command. When the part recovers automatically it uses 4-V as the threshold.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Intellectual 390 points

    Hello,

    I understood.

    Thank you,

    Takayama