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BQ40Z50-R3-DEVICE-FW: Host Watchdog (HWDF & CFETF)

JeremyG
Intellectual 610 points

Part Number: BQ40Z50-R3-DEVICE-FW

Hi,

We are using the bq40z50-R3 in a large format, 4S LiFePO4 pack and are trying to work out why PF faults are being triggered on some packs during charging. 

These faults are logged in the Black Box Recorder as;

HWDF in Safety Status/3rd Safety Status C.

CFETF in PF Status/1st PF Status C.

If these faults are related, it may suggest that the charger continues delivering current even after SMBus traffic ceases.  This is unexpected, as the CHGFET should prevent this from happening.  I have done some testing with bqstudio and an attached regulated power supply (connected as a charger) and confirmed that once SMBus traffic ceases and the 5 second HWD Delay timer subsequently expires, the CHGFET opens and interrupts the charge current, as expected.

I have also tried disabling the CHGFET with bqstudio and measuring leakage current (when the attached regulated power supply was set to the highest recommended voltage for the bq40z50 (26V)), but the FET prevented current flow, as expected.

I have read about similar issues elsewhere in this forum (some apparently still unresolved) and wondered if anyone has any advice or suggestions for troubleshooting this?

How does the gauge detect FET failure?

What does the 'F' in HWDF stand for?

In our application, the host reads Charging Voltage and Charging Current values from the pack and writes them to the Smart Charger once per second.

We have set the HWDF bit in Enabled Protections C to prevent dumb chargers from charging our pack.

Thank you,

Jeremy.

  • 0
    TI__Genius 10370 points

    Jeremy,

    The HWDF stands for "Host WatchDog Fault". You have it right. When there is no communication on the SMB line for X time, then the FETS will open. This however is a 1st level protection which is fully recoverable once communication is established. 

    THe CFETF is the big one. This is the gauge telling the FET to be open, but positive charge current is still detected across the senseR. it means the gauge was unable to stop charge current from flowing. I would review the schematic further making sure there is no unexpected current path. Any current above the threshold of 5mA (default) for the delay time will trigger this event. 

    This could be noise or an external load (that flows through the senseR). 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Intellectual 610 points

    Hi Vos,

    Is it possible that a temporary difference between the requested (0mA) and the actual current could trigger the CFETF fault, or is the condition strictly related to deactivation of the charge pump? 

    This could occur if the charger took 5 seconds to respond to the command.

    Regards,

    Jeremy.

  • +1 in reply to JeremyG
    TI__Guru** 102455 points

    Hello Jeremy,

    The failure is related to the actual current sense, not the requested. As Eric mentioned I would check your calibration to make sure there's no board offset needed, or check the schematic and make sure there's no unintended current paths causing CFETF to trigger.

    CFETF is activated when there's still current flowing even after the gauge deactivated the Chg FET.

    Sincerely,

    Wyatt Keller